From dc708480b286decd4328d52d742cac000faca3f8 Mon Sep 17 00:00:00 2001
From: "Brian S. O'Neill" <bronee@gmail.com>
Date: Sun, 4 May 2008 17:36:39 +0000
Subject: Merged map repository implementation from map branch.

---
 .../java/com/amazon/carbonado/repo/map/Key.java    |  273 +++++
 .../com/amazon/carbonado/repo/map/MapCursor.java   |  173 +++
 .../amazon/carbonado/repo/map/MapRepository.java   |  125 +++
 .../carbonado/repo/map/MapRepositoryBuilder.java   |  151 +++
 .../com/amazon/carbonado/repo/map/MapStorage.java  |  813 ++++++++++++++
 .../amazon/carbonado/repo/map/MapTransaction.java  |  240 ++++
 .../carbonado/repo/map/MapTransactionManager.java  |   98 ++
 .../amazon/carbonado/repo/map/UpgradableLock.java  | 1161 ++++++++++++++++++++
 .../amazon/carbonado/repo/map/package-info.java    |   24 +
 9 files changed, 3058 insertions(+)
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/Key.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/MapCursor.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/MapRepository.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/MapRepositoryBuilder.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/MapStorage.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/MapTransaction.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/MapTransactionManager.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/UpgradableLock.java
 create mode 100644 src/main/java/com/amazon/carbonado/repo/map/package-info.java

(limited to 'src/main/java')

diff --git a/src/main/java/com/amazon/carbonado/repo/map/Key.java b/src/main/java/com/amazon/carbonado/repo/map/Key.java
new file mode 100644
index 0000000..5032f66
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/Key.java
@@ -0,0 +1,273 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.lang.reflect.UndeclaredThrowableException;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+
+import org.cojen.classfile.ClassFile;
+import org.cojen.classfile.CodeBuilder;
+import org.cojen.classfile.Label;
+import org.cojen.classfile.LocalVariable;
+import org.cojen.classfile.MethodInfo;
+import org.cojen.classfile.Modifiers;
+import org.cojen.classfile.TypeDesc;
+
+import org.cojen.util.ClassInjector;
+import org.cojen.util.SoftValuedHashMap;
+
+import com.amazon.carbonado.Storable;
+
+import com.amazon.carbonado.info.OrderedProperty;
+import com.amazon.carbonado.info.StorableInfo;
+import com.amazon.carbonado.info.StorableIntrospector;
+import com.amazon.carbonado.info.StorableProperty;
+
+import com.amazon.carbonado.gen.CodeBuilderUtil;
+
+/**
+ * 
+ *
+ * @author Brian S O'Neill
+ */
+class Key<S extends Storable> implements Comparable<Key<S>> {
+    protected final S mStorable;
+    protected final Comparator<S> mComparator;
+
+    Key(S storable, Comparator<S> comparator) {
+        mStorable = storable;
+        mComparator = comparator;
+    }
+
+    @Override
+    public String toString() {
+        return mStorable.toString();
+    }
+
+    public int compareTo(Key<S> other) {
+        int result = mComparator.compare(mStorable, other.mStorable);
+        if (result == 0) {
+            int t1 = tieBreaker();
+            int t2 = other.tieBreaker();
+            if (t1 < t2) {
+                result = -1;
+            } else if (t1 > t2) {
+                result = 1;
+            }
+        }
+        return result;
+    }
+
+    protected int tieBreaker() {
+        return 0;
+    }
+
+    public static interface Assigner<S extends Storable> {
+        void setKeyValues(S storable, Object[] identityValues);
+
+        void setKeyValues(S storable, Object[] identityValues, Object rangeValue);
+    }
+
+    private static final Map<Class, Assigner> mAssigners;
+
+    static {
+        mAssigners = new SoftValuedHashMap();
+    }
+
+    public static synchronized <S extends Storable> Assigner<S> getAssigner(Class<S> clazz) {
+        Assigner<S> assigner = mAssigners.get(clazz);
+        if (assigner == null) {
+            assigner = createAssigner(clazz);
+            mAssigners.put(clazz, assigner);
+        }
+        return assigner;
+    }
+
+    private static <S extends Storable> Assigner<S> createAssigner(Class<S> clazz) {
+        final StorableInfo<S> info = StorableIntrospector.examine(clazz);
+
+        ClassInjector ci = ClassInjector.create(clazz.getName(), clazz.getClassLoader());
+        ClassFile cf = new ClassFile(ci.getClassName());
+        cf.addInterface(Assigner.class);
+        cf.markSynthetic();
+        cf.setSourceFile(Key.class.getName());
+        cf.setTarget("1.5");
+
+        cf.addDefaultConstructor();
+
+        // Define required setKeyValues methods.
+
+        List<OrderedProperty<S>> pk =
+            new ArrayList<OrderedProperty<S>>(info.getPrimaryKey().getProperties());
+
+        TypeDesc storableType = TypeDesc.forClass(Storable.class);
+        TypeDesc storableArrayType = storableType.toArrayType();
+        TypeDesc userStorableType = TypeDesc.forClass(info.getStorableType());
+        TypeDesc objectArrayType = TypeDesc.OBJECT.toArrayType();
+
+        MethodInfo mi = cf.addMethod(Modifiers.PUBLIC, "setKeyValues", null,
+                                     new TypeDesc[] {storableType, objectArrayType});
+
+        CodeBuilder b = new CodeBuilder(mi);
+
+        LocalVariable userStorableVar = b.createLocalVariable(null, userStorableType);
+        b.loadLocal(b.getParameter(0));
+        b.checkCast(userStorableType);
+        b.storeLocal(userStorableVar);
+
+        // Switch on the number of values supplied.
+
+        /* Switch looks like this for two pk properties:
+
+        switch(identityValues.length) {
+        default:
+            throw new IllegalArgumentException();
+        case 2:
+            storable.setPkProp2(identityValues[1]);
+        case 1:
+            storable.setPkProp1(identityValues[0]);
+        case 0:
+        }
+
+        */
+
+        b.loadLocal(b.getParameter(1));
+        b.arrayLength();
+
+        int[] cases = new int[pk.size() + 1];
+        Label[] labels = new Label[pk.size() + 1];
+
+        for (int i=0; i<labels.length; i++) {
+            cases[i] = pk.size() - i;
+            labels[i] = b.createLabel();
+        }
+
+        Label defaultLabel = b.createLabel();
+
+        b.switchBranch(cases, labels, defaultLabel);
+
+        for (int i=0; i<labels.length; i++) {
+            labels[i].setLocation();
+            int prop = cases[i] - 1;
+            if (prop >= 0) {
+                b.loadLocal(userStorableVar);
+                b.loadLocal(b.getParameter(1));
+                b.loadConstant(prop);
+                b.loadFromArray(storableArrayType);
+                callSetPropertyValue(b, pk.get(prop));
+            }
+            // Fall through to next case.
+        }
+
+        b.returnVoid();
+
+        defaultLabel.setLocation();
+        CodeBuilderUtil.throwException(b, IllegalArgumentException.class, null);
+
+        // The setKeyValues method that takes a range value calls the other
+        // setKeyValues method first, to take care of the identityValues.
+
+        mi = cf.addMethod(Modifiers.PUBLIC, "setKeyValues", null,
+                          new TypeDesc[] {storableType, objectArrayType, TypeDesc.OBJECT});
+
+        b = new CodeBuilder(mi);
+
+        b.loadThis();
+        b.loadLocal(b.getParameter(0));
+        b.loadLocal(b.getParameter(1));
+        b.invokeVirtual("setKeyValues", null, new TypeDesc[] {storableType, objectArrayType});
+
+        userStorableVar = b.createLocalVariable(null, userStorableType);
+        b.loadLocal(b.getParameter(0));
+        b.checkCast(userStorableType);
+        b.storeLocal(userStorableVar);
+
+        // Switch on the number of values supplied.
+
+        /* Switch looks like this for two pk properties:
+
+        switch(identityValues.length) {
+        default:
+            throw new IllegalArgumentException();
+        case 0:
+            storable.setPkProp1(rangeValue);
+            return;
+        case 1:
+            storable.setPkProp2(rangeValue);
+            return;
+        }
+
+        */
+
+        b.loadLocal(b.getParameter(1));
+        b.arrayLength();
+
+        cases = new int[pk.size()];
+        labels = new Label[pk.size()];
+
+        for (int i=0; i<labels.length; i++) {
+            cases[i] = i;
+            labels[i] = b.createLabel();
+        }
+
+        defaultLabel = b.createLabel();
+
+        b.switchBranch(cases, labels, defaultLabel);
+
+        for (int i=0; i<labels.length; i++) {
+            labels[i].setLocation();
+            int prop = cases[i];
+            b.loadLocal(userStorableVar);
+            b.loadLocal(b.getParameter(2));
+            callSetPropertyValue(b, pk.get(prop));
+            b.returnVoid();
+        }
+
+        defaultLabel.setLocation();
+        CodeBuilderUtil.throwException(b, IllegalArgumentException.class, null);
+
+        try {
+            return (Assigner<S>) ci.defineClass(cf).newInstance();
+        } catch (IllegalAccessException e) {
+            throw new UndeclaredThrowableException(e);
+        } catch (InstantiationException e) {
+            throw new UndeclaredThrowableException(e);
+        }
+    }
+
+    /**
+     * Creates code to call set method. Assumes Storable and property value
+     * are already on the stack.
+     */
+    private static void callSetPropertyValue(CodeBuilder b, OrderedProperty<?> op) {
+        StorableProperty<?> property = op.getChainedProperty().getLastProperty();
+        TypeDesc propType = TypeDesc.forClass(property.getType());
+        if (propType != TypeDesc.OBJECT) {
+            TypeDesc objectType = propType.toObjectType();
+            b.checkCast(objectType);
+            // Potentially unbox primitive.
+            b.convert(objectType, propType);
+        }
+        b.invoke(property.getWriteMethod());
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/MapCursor.java b/src/main/java/com/amazon/carbonado/repo/map/MapCursor.java
new file mode 100644
index 0000000..cd0f7e3
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/MapCursor.java
@@ -0,0 +1,173 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.util.ConcurrentModificationException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+import com.amazon.carbonado.FetchException;
+import com.amazon.carbonado.IsolationLevel;
+import com.amazon.carbonado.Storable;
+
+import com.amazon.carbonado.cursor.AbstractCursor;
+
+import com.amazon.carbonado.spi.TransactionScope;
+
+/**
+ * Returns copies of Storables that it iterates over.
+ *
+ * @author Brian S O'Neill
+ */
+class MapCursor<S extends Storable> extends AbstractCursor<S> {
+    private static final AtomicReferenceFieldUpdater<MapCursor, Iterator> cIteratorRef =
+        AtomicReferenceFieldUpdater.newUpdater
+        (MapCursor.class, Iterator.class, "mIterator");
+
+    private final MapStorage<S> mStorage;
+    private final TransactionScope<MapTransaction> mScope;
+    private final MapTransaction mTxn;
+    private final boolean mIsForUpdate;
+
+    private volatile Iterator<S> mIterator;
+
+    MapCursor(MapStorage<S> storage,
+              TransactionScope<MapTransaction> scope,
+              Iterable<S> iterable)
+        throws Exception
+    {
+        MapTransaction txn = scope.getTxn();
+
+        mStorage = storage;
+        mScope = scope;
+        mTxn = txn;
+
+        if (txn == null) {
+            mStorage.mLock.lockForRead(scope);
+            mIsForUpdate = false;
+        } else {
+            // Since lock is so coarse, all reads in transaction scope are
+            // upgrade to avoid deadlocks.
+            txn.lockForUpgrade(mStorage.mLock, mIsForUpdate = scope.isForUpdate());
+        }
+
+        scope.register(storage.getStorableType(), this);
+        mIterator = iterable.iterator();
+    }
+
+    public void close() {
+        Iterator<S> it = mIterator;
+        if (it != null) {
+            if (cIteratorRef.compareAndSet(this, it, null)) {
+                UpgradableLock lock = mStorage.mLock;
+                if (mTxn == null) {
+                    lock.unlockFromRead(mScope);
+                } else {
+                    mTxn.unlockFromUpgrade(lock, mIsForUpdate);
+                }
+                mScope.unregister(mStorage.getStorableType(), this);
+            }
+        }
+    }
+
+    public boolean hasNext() throws FetchException {
+        Iterator<S> it = mIterator;
+        try {
+            if (it != null && it.hasNext()) {
+                return true;
+            } else {
+                close();
+            }
+            return false;
+        } catch (ConcurrentModificationException e) {
+            close();
+            throw new FetchException(e);
+        } catch (Error e) {
+            try {
+                close();
+            } catch (Error e2) {
+                // Ignore.
+            }
+            throw e;
+        }
+    }
+
+    public S next() throws FetchException {
+        Iterator<S> it = mIterator;
+        if (it == null) {
+            close();
+            throw new NoSuchElementException();
+        }
+        try {
+            S next = mStorage.copyAndFireLoadTrigger(it.next());
+            if (!hasNext()) {
+                close();
+            }
+            return next;
+        } catch (ConcurrentModificationException e) {
+            close();
+            throw new FetchException(e);
+        } catch (Error e) {
+            try {
+                close();
+            } catch (Error e2) {
+                // Ignore.
+            }
+            throw e;
+        }
+    }
+
+    @Override
+    public int skipNext(int amount) throws FetchException {
+        if (amount <= 0) {
+            if (amount < 0) {
+                throw new IllegalArgumentException("Cannot skip negative amount: " + amount);
+            }
+            return 0;
+        }
+
+        // Skip over entries without copying them.
+
+        int count = 0;
+        Iterator<S> it = mIterator;
+
+        if (it != null) {
+            try {
+                while (--amount >= 0 && it.hasNext()) {
+                    it.next();
+                    count++;
+                }
+            } catch (ConcurrentModificationException e) {
+                close();
+                throw new FetchException(e);
+            } catch (Error e) {
+                try {
+                    close();
+                } catch (Error e2) {
+                    // Ignore.
+                }
+                throw e;
+            }
+        }
+
+        return count;
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/MapRepository.java b/src/main/java/com/amazon/carbonado/repo/map/MapRepository.java
new file mode 100644
index 0000000..2e82f89
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/MapRepository.java
@@ -0,0 +1,125 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.commons.logging.Log;
+
+import com.amazon.carbonado.Repository;
+import com.amazon.carbonado.RepositoryException;
+import com.amazon.carbonado.Storable;
+import com.amazon.carbonado.Storage;
+import com.amazon.carbonado.TriggerFactory;
+
+import com.amazon.carbonado.capability.IndexInfo;
+import com.amazon.carbonado.capability.IndexInfoCapability;
+
+import com.amazon.carbonado.sequence.SequenceValueGenerator;
+import com.amazon.carbonado.sequence.SequenceValueProducer;
+
+import com.amazon.carbonado.qe.RepositoryAccess;
+import com.amazon.carbonado.qe.StorageAccess;
+
+import com.amazon.carbonado.spi.AbstractRepository;
+import com.amazon.carbonado.spi.LobEngine;
+import com.amazon.carbonado.spi.TransactionManager;
+import com.amazon.carbonado.spi.TransactionScope;
+
+/**
+ * 
+ *
+ * @author Brian S O'Neill
+ * @see MapRepositoryBuilder
+ */
+class MapRepository extends AbstractRepository<MapTransaction>
+    implements RepositoryAccess, IndexInfoCapability
+{
+    private final AtomicReference<Repository> mRootRef;
+    private final boolean mIsMaster;
+    private final int mLockTimeout;
+    private final TimeUnit mLockTimeoutUnit;
+
+    final Iterable<TriggerFactory> mTriggerFactories;
+    private final MapTransactionManager mTxnManager;
+    private LobEngine mLobEngine;
+
+    MapRepository(AtomicReference<Repository> rootRef, MapRepositoryBuilder builder) {
+        super(builder.getName());
+        mRootRef = rootRef;
+        mIsMaster = builder.isMaster();
+        mLockTimeout = builder.getLockTimeout();
+        mLockTimeoutUnit = builder.getLockTimeoutUnit();
+
+        mTriggerFactories = builder.getTriggerFactories();
+        mTxnManager = new MapTransactionManager(mLockTimeout, mLockTimeoutUnit);
+    }
+
+    public Repository getRootRepository() {
+        return mRootRef.get();
+    }
+
+    public <S extends Storable> StorageAccess<S> storageAccessFor(Class<S> type)
+        throws RepositoryException
+    {
+        return (StorageAccess<S>) storageFor(type);
+    }
+
+    public <S extends Storable> IndexInfo[] getIndexInfo(Class<S> storableType)
+        throws RepositoryException
+    {
+        return ((MapStorage) storageFor(storableType)).getIndexInfo();
+    }
+
+    protected Log getLog() {
+        return null;
+    }
+
+    protected TransactionManager<MapTransaction> transactionManager() {
+        return mTxnManager;
+    }
+
+    protected TransactionScope<MapTransaction> localTransactionScope() {
+        return mTxnManager.localScope();
+    }
+
+    protected <S extends Storable> Storage<S> createStorage(Class<S> type)
+        throws RepositoryException
+    {
+        return new MapStorage<S>(this, type, mLockTimeout, mLockTimeoutUnit);
+    }
+
+    protected SequenceValueProducer createSequenceValueProducer(String name)
+        throws RepositoryException
+    {
+        return new SequenceValueGenerator(this, name);
+    }
+
+    LobEngine getLobEngine() throws RepositoryException {
+        if (mLobEngine == null) {
+            mLobEngine = new LobEngine(this, getRootRepository());
+        }
+        return mLobEngine;
+    }
+
+    boolean isMaster() {
+        return mIsMaster;
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/MapRepositoryBuilder.java b/src/main/java/com/amazon/carbonado/repo/map/MapRepositoryBuilder.java
new file mode 100644
index 0000000..8d5d399
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/MapRepositoryBuilder.java
@@ -0,0 +1,151 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.TimeUnit;
+
+import com.amazon.carbonado.Repository;
+import com.amazon.carbonado.RepositoryException;
+
+import com.amazon.carbonado.repo.indexed.IndexedRepositoryBuilder;
+
+import com.amazon.carbonado.spi.AbstractRepositoryBuilder;
+
+/**
+ * Volatile repository implementation backed by a concurrent map. Locks used by
+ * repository are coarse, much like <i>table locks</i>. Loads and queries
+ * acquire read locks, and modifications acquire write locks. Within
+ * transactions, loads and queries always acquire upgradable locks, to reduce
+ * the likelihood of deadlock.
+ *
+ * <p>This repository supports transactions, which also may be
+ * nested. Supported isolation levels are read committed and serializable. Read
+ * uncommitted is promoted to read committed, and repeatable read is promoted
+ * to serializable.
+ *
+ * <p>
+ * The following extra capabilities are supported:
+ * <ul>
+ * <li>{@link com.amazon.carbonado.capability.IndexInfoCapability IndexInfoCapability}
+ * <li>{@link com.amazon.carbonado.capability.ShutdownCapability ShutdownCapability}
+ * <li>{@link com.amazon.carbonado.sequence.SequenceCapability SequenceCapability}
+ * </ul>
+ *
+ * <p>Note: This repository uses concurrent navigable map classes, which became
+ * available in JDK1.6.
+ *
+ * @author Brian S O'Neill
+ * @since 1.2
+ */
+public class MapRepositoryBuilder extends AbstractRepositoryBuilder {
+    /**
+     * Convenience method to build a new MapRepository.
+     */
+    public static Repository newRepository() {
+        try {
+            MapRepositoryBuilder builder = new MapRepositoryBuilder();
+            return builder.build();
+        } catch (RepositoryException e) {
+            // Not expected.
+            throw new RuntimeException(e);
+        }
+    }
+
+    private String mName = "";
+    private boolean mIsMaster = true;
+    private boolean mIndexSupport = true;
+    private int mLockTimeout;
+    private TimeUnit mLockTimeoutUnit;
+
+    public MapRepositoryBuilder() {
+        setLockTimeoutMillis(500);
+    }
+
+    public Repository build(AtomicReference<Repository> rootRef) throws RepositoryException {
+        if (mIndexSupport) {
+            // Temporarily set to false to avoid infinite recursion.
+            mIndexSupport = false;
+            try {
+                IndexedRepositoryBuilder ixBuilder = new IndexedRepositoryBuilder();
+                ixBuilder.setWrappedRepository(this);
+                ixBuilder.setMaster(isMaster());
+                ixBuilder.setAllClustered(true);
+                return ixBuilder.build(rootRef);
+            } finally {
+                mIndexSupport = true;
+            }
+        }
+
+        assertReady();
+
+        Repository repo = new MapRepository(rootRef, this);
+
+        rootRef.set(repo);
+        return repo;
+    }
+
+    public String getName() {
+        return mName;
+    }
+
+    public void setName(String name) {
+        mName = name;
+    }
+
+    public boolean isMaster() {
+        return mIsMaster;
+    }
+
+    public void setMaster(boolean b) {
+        mIsMaster = b;
+    }
+
+    /**
+     * Set the lock timeout, in milliseconds. Default value is 500 milliseconds.
+     */
+    public void setLockTimeoutMillis(int timeout) {
+        setLockTimeout(timeout, TimeUnit.MILLISECONDS);
+    }
+
+    /**
+     * Set the lock timeout. Default value is 500 milliseconds.
+     */
+    public void setLockTimeout(int timeout, TimeUnit unit) {
+        if (timeout < 0 || unit == null) {
+            throw new IllegalArgumentException();
+        }
+        mLockTimeout = timeout;
+        mLockTimeoutUnit = unit;
+    }
+
+    /**
+     * Returns the lock timeout. Call getLockTimeoutUnit to get the unit.
+     */
+    public int getLockTimeout() {
+        return mLockTimeout;
+    }
+
+    /**
+     * Returns the lock timeout unit. Call getLockTimeout to get the timeout.
+     */
+    public TimeUnit getLockTimeoutUnit() {
+        return mLockTimeoutUnit;
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/MapStorage.java b/src/main/java/com/amazon/carbonado/repo/map/MapStorage.java
new file mode 100644
index 0000000..520d18c
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/MapStorage.java
@@ -0,0 +1,813 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.EnumSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.NavigableMap;
+import java.util.Set;
+
+import java.util.concurrent.ConcurrentNavigableMap;
+import java.util.concurrent.ConcurrentSkipListMap;
+import java.util.concurrent.TimeUnit;
+
+import org.cojen.classfile.TypeDesc;
+
+import com.amazon.carbonado.Cursor;
+import com.amazon.carbonado.FetchException;
+import com.amazon.carbonado.FetchInterruptedException;
+import com.amazon.carbonado.FetchTimeoutException;
+import com.amazon.carbonado.IsolationLevel;
+import com.amazon.carbonado.PersistException;
+import com.amazon.carbonado.PersistInterruptedException;
+import com.amazon.carbonado.PersistTimeoutException;
+import com.amazon.carbonado.Query;
+import com.amazon.carbonado.Repository;
+import com.amazon.carbonado.RepositoryException;
+import com.amazon.carbonado.Storable;
+import com.amazon.carbonado.Storage;
+import com.amazon.carbonado.SupportException;
+import com.amazon.carbonado.Trigger;
+
+import com.amazon.carbonado.capability.IndexInfo;
+
+import com.amazon.carbonado.cursor.ArraySortBuffer;
+import com.amazon.carbonado.cursor.EmptyCursor;
+import com.amazon.carbonado.cursor.FilteredCursor;
+import com.amazon.carbonado.cursor.SingletonCursor;
+import com.amazon.carbonado.cursor.SortBuffer;
+import com.amazon.carbonado.cursor.SortedCursor;
+
+import com.amazon.carbonado.filter.Filter;
+import com.amazon.carbonado.filter.FilterValues;
+import com.amazon.carbonado.filter.RelOp;
+
+import com.amazon.carbonado.sequence.SequenceValueProducer;
+
+import com.amazon.carbonado.gen.DelegateStorableGenerator;
+import com.amazon.carbonado.gen.DelegateSupport;
+import com.amazon.carbonado.gen.MasterFeature;
+
+import com.amazon.carbonado.util.QuickConstructorGenerator;
+
+import com.amazon.carbonado.filter.Filter;
+
+import com.amazon.carbonado.info.ChainedProperty;
+import com.amazon.carbonado.info.Direction;
+import com.amazon.carbonado.info.OrderedProperty;
+import com.amazon.carbonado.info.StorableIndex;
+import com.amazon.carbonado.info.StorableInfo;
+import com.amazon.carbonado.info.StorableIntrospector;
+import com.amazon.carbonado.info.StorableProperty;
+
+import com.amazon.carbonado.qe.BoundaryType;
+import com.amazon.carbonado.qe.QueryExecutorFactory;
+import com.amazon.carbonado.qe.QueryEngine;
+import com.amazon.carbonado.qe.StorageAccess;
+
+import com.amazon.carbonado.spi.IndexInfoImpl;
+import com.amazon.carbonado.spi.LobEngine;
+import com.amazon.carbonado.spi.TransactionScope;
+import com.amazon.carbonado.spi.TriggerManager;
+
+/**
+ * 
+ *
+ * @author Brian S O'Neill
+ */
+class MapStorage<S extends Storable> 
+    implements Storage<S>, DelegateSupport<S>, StorageAccess<S>
+{
+    private static final int DEFAULT_LOB_BLOCK_SIZE = 1000;
+    private static final Object[] NO_VALUES = new Object[0];
+
+    private final MapRepository mRepo;
+    private final StorableInfo<S> mInfo;
+    private final TriggerManager<S> mTriggers;
+    private final InstanceFactory mInstanceFactory;
+    private final StorableIndex<S> mPrimaryKeyIndex;
+    private final QueryEngine<S> mQueryEngine;
+
+    private final int mLockTimeout;
+    private final TimeUnit mLockTimeoutUnit;
+
+    private final ConcurrentNavigableMap<Key<S>, S> mMap;
+    private final Comparator<S> mFullComparator;
+    private final Comparator<S>[] mSearchComparators;
+
+    private final Key.Assigner<S> mKeyAssigner;
+
+    /**
+     * Simple lock which is reentrant for transactions, but auto-commit does not
+     * need to support reentrancy. Read lock requests in transactions can starve
+     * write lock requests, but auto-commit cannot cause starvation. In practice
+     * starvation is not possible since transactions always lock for upgrade.
+     */
+    final UpgradableLock<Object> mLock = new UpgradableLock<Object>() {
+        @Override
+        protected boolean isReadLockHeld(Object locker) {
+            return locker instanceof MapTransaction;
+        }
+    };
+
+    MapStorage(MapRepository repo, Class<S> type, int lockTimeout, TimeUnit lockTimeoutUnit)
+        throws SupportException
+    {
+        mRepo = repo;
+        mInfo = StorableIntrospector.examine(type);
+        mTriggers = new TriggerManager<S>();
+
+        EnumSet<MasterFeature> features;
+        if (repo.isMaster()) {
+            features = EnumSet.of(MasterFeature.INSERT_CHECK_REQUIRED,
+                                  MasterFeature.VERSIONING,
+                                  MasterFeature.INSERT_SEQUENCES);
+        } else {
+            features = EnumSet.of(MasterFeature.INSERT_CHECK_REQUIRED);
+        }
+
+        Class<? extends S> delegateStorableClass =
+            DelegateStorableGenerator.getDelegateClass(type, features);
+
+        mInstanceFactory = QuickConstructorGenerator
+            .getInstance(delegateStorableClass, InstanceFactory.class);
+
+        mPrimaryKeyIndex =
+            new StorableIndex<S>(mInfo.getPrimaryKey(), Direction.ASCENDING).clustered(true);
+
+        mQueryEngine = new QueryEngine<S>(type, repo);
+
+        mLockTimeout = lockTimeout;
+        mLockTimeoutUnit = lockTimeoutUnit;
+
+        mMap = new ConcurrentSkipListMap<Key<S>, S>();
+        List<OrderedProperty<S>> propList = createPkPropList();
+        mFullComparator = SortedCursor.createComparator(propList);
+        mSearchComparators = new Comparator[propList.size() + 1];
+        mSearchComparators[propList.size()] = mFullComparator;
+
+        mKeyAssigner = Key.getAssigner(type);
+
+        try {
+            if (LobEngine.hasLobs(type)) {
+                Trigger<S> lobTrigger = repo.getLobEngine()
+                    .getSupportTrigger(type, DEFAULT_LOB_BLOCK_SIZE);
+                addTrigger(lobTrigger);
+            }
+
+            // Don't install automatic triggers until we're completely ready.
+            mTriggers.addTriggers(type, repo.mTriggerFactories);
+        } catch (SupportException e) {
+            throw e;
+        } catch (RepositoryException e) {
+            throw new SupportException(e);
+        }
+    }
+
+    public Class<S> getStorableType() {
+        return mInfo.getStorableType();
+    }
+
+    public S prepare() {
+        return (S) mInstanceFactory.instantiate(this);
+    }
+
+    public Query<S> query() throws FetchException {
+        return mQueryEngine.query();
+    }
+
+    public Query<S> query(String filter) throws FetchException {
+        return mQueryEngine.query(filter);
+    }
+
+    public Query<S> query(Filter<S> filter) throws FetchException {
+        return mQueryEngine.query(filter);
+    }
+
+    public void truncate() throws PersistException {
+        try {
+            Object locker = mRepo.localTransactionScope().getTxn();
+            if (locker == null) {
+                locker = Thread.currentThread();
+            }
+            doLockForWrite(locker);
+            try {
+                mMap.clear();
+            } finally {
+                mLock.unlockFromWrite(locker);
+            }
+        } catch (PersistException e) {
+            throw e;
+        } catch (Exception e) {
+            throw new PersistException(e);
+        }
+    }
+
+    public boolean addTrigger(Trigger<? super S> trigger) {
+        return mTriggers.addTrigger(trigger);
+    }
+
+    public boolean removeTrigger(Trigger<? super S> trigger) {
+        return mTriggers.removeTrigger(trigger);
+    }
+
+    public IndexInfo[] getIndexInfo() {
+        StorableIndex<S> pkIndex = mPrimaryKeyIndex;
+
+        if (pkIndex == null) {
+            return new IndexInfo[0];
+        }
+
+        int i = pkIndex.getPropertyCount();
+        String[] propertyNames = new String[i];
+        Direction[] directions = new Direction[i];
+        while (--i >= 0) {
+            propertyNames[i] = pkIndex.getProperty(i).getName();
+            directions[i] = pkIndex.getPropertyDirection(i);
+        }
+
+        return new IndexInfo[] {
+            new IndexInfoImpl(getStorableType().getName(), true, true, propertyNames, directions)
+        };
+    }
+
+    public boolean doTryLoad(S storable) throws FetchException {
+        try {
+            TransactionScope<MapTransaction> scope = mRepo.localTransactionScope();
+            MapTransaction txn = scope.getTxn();
+            if (txn == null) {
+                doLockForRead(scope);
+                try {
+                    return doTryLoadNoLock(storable);
+                } finally {
+                    mLock.unlockFromRead(scope);
+                }
+            } else {
+                // Since lock is so coarse, all reads in transaction scope are
+                // upgrade to avoid deadlocks.
+                final boolean isForUpdate = scope.isForUpdate();
+                txn.lockForUpgrade(mLock, isForUpdate);
+                try {
+                    return doTryLoadNoLock(storable);
+                } finally {
+                    txn.unlockFromUpgrade(mLock, isForUpdate);
+                }
+            }
+        } catch (FetchException e) {
+            throw e;
+        } catch (Exception e) {
+            throw new FetchException(e);
+        }
+    }
+
+    // Caller must hold lock.
+    boolean doTryLoadNoLock(S storable) {
+        S existing = mMap.get(new Key<S>(storable, mFullComparator));
+        if (existing == null) {
+            return false;
+        } else {
+            storable.markAllPropertiesDirty();
+            existing.copyAllProperties(storable);
+            storable.markAllPropertiesClean();
+            return true;
+        }
+    }
+
+    public boolean doTryInsert(S storable) throws PersistException {
+        try {
+            TransactionScope<MapTransaction> scope = mRepo.localTransactionScope();
+            MapTransaction txn = scope.getTxn();
+            if (txn == null) {
+                // No need to acquire full write lock since map is concurrent
+                // and existing storable (if any) is not being
+                // modified. Upgrade lock is required because a concurrent
+                // transaction might be in progress, and so insert should wait.
+                doLockForUpgrade(scope);
+                try {
+                    return doTryInsertNoLock(storable);
+                } finally {
+                    mLock.unlockFromUpgrade(scope);
+                }
+            } else {
+                txn.lockForWrite(mLock);
+                if (doTryInsertNoLock(storable)) {
+                    txn.inserted(this, storable);
+                    return true;
+                } else {
+                    return false;
+                }
+            }
+        } catch (PersistException e) {
+            throw e;
+        } catch (FetchException e) {
+            throw e.toPersistException();
+        } catch (Exception e) {
+            throw new PersistException(e);
+        }
+    }
+
+    // Caller must hold upgrade or write lock.
+    private boolean doTryInsertNoLock(S storable) {
+        Key<S> key = new Key<S>(storable, mFullComparator);
+        S existing = mMap.get(key);
+        if (existing != null) {
+            return false;
+        }
+        // Create a fresh copy to ensure that custom fields are not saved.
+        S copy = (S) storable.prepare();
+        storable.copyAllProperties(copy);
+        copy.markAllPropertiesClean();
+        mMap.put(key, copy);
+        storable.markAllPropertiesClean();
+        return true;
+    }
+
+    public boolean doTryUpdate(S storable) throws PersistException {
+        try {
+            TransactionScope<MapTransaction> scope = mRepo.localTransactionScope();
+            MapTransaction txn = scope.getTxn();
+            if (txn == null) {
+                // Full write lock is required since existing storable is being
+                // modified. Readers cannot be allowed to see modifications
+                // until they are complete. In addtion, a concurrent
+                // transaction might be in progress, and so update should wait.
+                doLockForWrite(scope);
+                try {
+                    return doTryUpdateNoLock(storable);
+                } finally {
+                    mLock.unlockFromWrite(scope);
+                }
+            } else {
+                txn.lockForWrite(mLock);
+                S existing = mMap.get(new Key<S>(storable, mFullComparator));
+                if (existing == null) {
+                    return false;
+                } else {
+                    // Copy existing object to undo log.
+                    txn.updated(this, (S) existing.copy());
+
+                    // Copy altered values to existing object.
+                    existing.markAllPropertiesDirty();
+                    storable.copyDirtyProperties(existing);
+                    existing.markAllPropertiesClean();
+
+                    // Copy all values to user object, to simulate a reload.
+                    storable.markAllPropertiesDirty();
+                    existing.copyAllProperties(storable);
+                    storable.markAllPropertiesClean();
+
+                    return true;
+                }
+            }
+        } catch (PersistException e) {
+            throw e;
+        } catch (Exception e) {
+            throw new PersistException(e);
+        }
+    }
+
+    // Caller must hold write lock.
+    private boolean doTryUpdateNoLock(S storable) {
+        S existing = mMap.get(new Key<S>(storable, mFullComparator));
+        if (existing == null) {
+            return false;
+        } else {
+            // Copy altered values to existing object.
+            existing.markAllPropertiesDirty();
+            storable.copyDirtyProperties(existing);
+            existing.markAllPropertiesClean();
+
+            // Copy all values to user object, to simulate a reload.
+            storable.markAllPropertiesDirty();
+            existing.copyAllProperties(storable);
+            storable.markAllPropertiesClean();
+
+            return true;
+        }
+    }
+
+    public boolean doTryDelete(S storable) throws PersistException {
+        try {
+            TransactionScope<MapTransaction> scope = mRepo.localTransactionScope();
+            MapTransaction txn = scope.getTxn();
+            if (txn == null) {
+                // No need to acquire full write lock since map is concurrent
+                // and existing storable (if any) is not being
+                // modified. Upgrade lock is required because a concurrent
+                // transaction might be in progress, and so delete should wait.
+                doLockForUpgrade(scope);
+                try {
+                    return doTryDeleteNoLock(storable);
+                } finally {
+                    mLock.unlockFromUpgrade(scope);
+                }
+            } else {
+                txn.lockForWrite(mLock);
+                S existing = mMap.remove(new Key<S>(storable, mFullComparator));
+                if (existing == null) {
+                    return false;
+                } else {
+                    txn.deleted(this, existing);
+                    return true;
+                }
+            }
+        } catch (PersistException e) {
+            throw e;
+        } catch (FetchException e) {
+            throw e.toPersistException();
+        } catch (Exception e) {
+            throw new PersistException(e);
+        }
+    }
+
+    // Caller must hold upgrade or write lock.
+    private boolean doTryDeleteNoLock(S storable) {
+        return mMap.remove(new Key<S>(storable, mFullComparator)) != null;
+    }
+
+    // Called by MapTransaction, which implicitly holds lock.
+    void mapPut(S storable) {
+        mMap.put(new Key<S>(storable, mFullComparator), storable);
+    }
+
+    // Called by MapTransaction, which implicitly holds lock.
+    void mapRemove(S storable) {
+        mMap.remove(new Key<S>(storable, mFullComparator));
+    }
+
+    private void doLockForRead(Object locker) throws FetchException {
+        try {
+            if (!mLock.tryLockForRead(locker, mLockTimeout, mLockTimeoutUnit)) {
+                throw new FetchTimeoutException("" + mLockTimeout + ' ' +
+                                                mLockTimeoutUnit.toString().toLowerCase());
+            }
+        } catch (InterruptedException e) {
+            throw new FetchInterruptedException(e);
+        }
+    }
+
+    private void doLockForUpgrade(Object locker) throws FetchException {
+        try {
+            if (!mLock.tryLockForUpgrade(locker, mLockTimeout, mLockTimeoutUnit)) {
+                throw new FetchTimeoutException("" + mLockTimeout + ' ' +
+                                                mLockTimeoutUnit.toString().toLowerCase());
+            }
+        } catch (InterruptedException e) {
+            throw new FetchInterruptedException(e);
+        }
+    }
+
+    private void doLockForWrite(Object locker) throws PersistException {
+        try {
+            if (!mLock.tryLockForWrite(locker, mLockTimeout, mLockTimeoutUnit)) {
+                throw new PersistTimeoutException("" + mLockTimeout + ' ' +
+                                                  mLockTimeoutUnit.toString().toLowerCase());
+            }
+        } catch (InterruptedException e) {
+            throw new PersistInterruptedException(e);
+        }
+    }
+
+    public Repository getRootRepository() {
+        return mRepo.getRootRepository();
+    }
+
+    public boolean isPropertySupported(String propertyName) {
+        return mInfo.getAllProperties().containsKey(propertyName);
+    }
+
+    public Trigger<? super S> getInsertTrigger() {
+        return mTriggers.getInsertTrigger();
+    }
+
+    public Trigger<? super S> getUpdateTrigger() {
+        return mTriggers.getUpdateTrigger();
+    }
+
+    public Trigger<? super S> getDeleteTrigger() {
+        return mTriggers.getDeleteTrigger();
+    }
+
+    public Trigger<? super S> getLoadTrigger() {
+        return mTriggers.getLoadTrigger();
+    }
+
+    public void locallyDisableLoadTrigger() {
+        mTriggers.locallyDisableLoad();
+    }
+
+    public void locallyEnableLoadTrigger() {
+        mTriggers.locallyEnableLoad();
+    }
+
+    public SequenceValueProducer getSequenceValueProducer(String name) throws PersistException {
+        try {
+            return mRepo.getSequenceValueProducer(name);
+        } catch (RepositoryException e) {
+            throw e.toPersistException();
+        }
+    }
+
+    public QueryExecutorFactory<S> getQueryExecutorFactory() {
+        return mQueryEngine;
+    }
+
+    public Collection<StorableIndex<S>> getAllIndexes() {
+        return Collections.singletonList(mPrimaryKeyIndex);
+    }
+
+    public Storage<S> storageDelegate(StorableIndex<S> index) {
+        // We're the grunt and don't delegate.
+        return null;
+    }
+
+    public long countAll() throws FetchException {
+        try {
+            Object locker = mRepo.localTransactionScope().getTxn();
+            if (locker == null) {
+                locker = Thread.currentThread();
+            }
+            doLockForRead(locker);
+            try {
+                return mMap.size();
+            } finally {
+                mLock.unlockFromRead(locker);
+            }
+        } catch (FetchException e) {
+            throw e;
+        } catch (Exception e) {
+            throw new FetchException(e);
+        }
+    }
+
+    public Cursor<S> fetchAll() throws FetchException {
+        try {
+            return new MapCursor<S>(this, mRepo.localTransactionScope(), mMap.values());
+        } catch (FetchException e) {
+            throw e;
+        } catch (Exception e) {
+            throw new FetchException(e);
+        }
+    }
+
+    public Cursor<S> fetchOne(StorableIndex<S> index, Object[] identityValues)
+        throws FetchException
+    {
+        try {
+            S key = prepare();
+            for (int i=0; i<identityValues.length; i++) {
+                key.setPropertyValue(index.getProperty(i).getName(), identityValues[i]);
+            }
+
+            TransactionScope<MapTransaction> scope = mRepo.localTransactionScope();
+            MapTransaction txn = scope.getTxn();
+            if (txn == null) {
+                doLockForRead(scope);
+                try {
+                    S value = mMap.get(new Key<S>(key, mFullComparator));
+                    if (value == null) {
+                        return EmptyCursor.the();
+                    } else {
+                        return new SingletonCursor<S>(copyAndFireLoadTrigger(value));
+                    }
+                } finally {
+                    mLock.unlockFromRead(scope);
+                }
+            } else {
+                // Since lock is so coarse, all reads in transaction scope are
+                // upgrade to avoid deadlocks.
+                final boolean isForUpdate = scope.isForUpdate();
+                txn.lockForUpgrade(mLock, isForUpdate);
+                try {
+                    S value = mMap.get(new Key<S>(key, mFullComparator));
+                    if (value == null) {
+                        return EmptyCursor.the();
+                    } else {
+                        return new SingletonCursor<S>(copyAndFireLoadTrigger(value));
+                    }
+                } finally {
+                    txn.unlockFromUpgrade(mLock, isForUpdate);
+                }
+            }
+        } catch (FetchException e) {
+            throw e;
+        } catch (Exception e) {
+            throw new FetchException(e);
+        }
+    }
+
+    S copyAndFireLoadTrigger(S storable) throws FetchException {
+        storable = (S) storable.copy();
+        Trigger<? super S> trigger = getLoadTrigger();
+        if (trigger != null) {
+            trigger.afterLoad(storable);
+            // In case trigger modified the properties, make sure they're still clean.
+            storable.markAllPropertiesClean();
+        }
+        return storable;
+    }
+
+    public Query<?> indexEntryQuery(StorableIndex<S> index) {
+        return null;
+    }
+
+    public Cursor<S> fetchFromIndexEntryQuery(StorableIndex<S> index, Query<?> indexEntryQuery) {
+        return null;
+    }
+
+    public Cursor<S> fetchSubset(StorableIndex<S> index,
+                                 Object[] identityValues,
+                                 BoundaryType rangeStartBoundary,
+                                 Object rangeStartValue,
+                                 BoundaryType rangeEndBoundary,
+                                 Object rangeEndValue,
+                                 boolean reverseRange,
+                                 boolean reverseOrder)
+        throws FetchException
+    {
+        if (identityValues == null) {
+            identityValues = NO_VALUES;
+        }
+
+        NavigableMap<Key<S>, S> map = mMap;
+
+        int tieBreaker = 1;
+        if (reverseOrder) {
+            map = map.descendingMap();
+            reverseRange = !reverseRange;
+            tieBreaker = -tieBreaker;
+        }
+
+        if (reverseRange) {
+            BoundaryType t1 = rangeStartBoundary;
+            rangeStartBoundary = rangeEndBoundary;
+            rangeEndBoundary = t1;
+            Object t2 = rangeStartValue;
+            rangeStartValue = rangeEndValue;
+            rangeEndValue = t2;
+        }
+
+        tail: {
+            Key<S> startKey;
+            switch (rangeStartBoundary) {
+            case OPEN: default:
+                if (identityValues.length == 0) {
+                    break tail;
+                } else {
+                    // Tie breaker of -1 puts search key right before first actual
+                    // match, thus forming an inclusive start match.
+                    startKey = searchKey(-tieBreaker, identityValues);
+                }
+                break;
+            case INCLUSIVE:
+                // Tie breaker of -1 puts search key right before first actual
+                // match, thus forming an inclusive start match.
+                startKey = searchKey(-tieBreaker, identityValues, rangeStartValue);
+                break;
+            case EXCLUSIVE:
+                // Tie breaker of +1 puts search key right after first actual
+                // match, thus forming an exlusive start match.
+                startKey = searchKey(tieBreaker, identityValues, rangeStartValue);
+                break;
+            }
+
+            map = map.tailMap(startKey, true);
+        }
+
+        Cursor<S> cursor;
+        try {
+            cursor = new MapCursor<S>(this, mRepo.localTransactionScope(), map.values());
+        } catch (FetchException e) {
+            throw e;
+        } catch (Exception e) {
+            throw new FetchException(e);
+        }
+
+        // Use filter to stop cursor at desired ending position.
+
+        // FIXME: Let query engine do this so that filter can be
+        // cached. Somehow indicate this at a high level so that query plan
+        // shows a filter.
+        Filter<S> filter;
+        FilterValues<S> filterValues;
+
+        if (rangeEndBoundary == BoundaryType.OPEN) {
+            if (identityValues.length == 0) {
+                filter = null;
+                filterValues = null;
+            } else {
+                filter = Filter.getOpenFilter(getStorableType());
+                for (int i=0; i<identityValues.length; i++) {
+                    filter = filter.and(index.getProperty(i).getName(), RelOp.EQ);
+                }
+                filterValues = filter.initialFilterValues();
+                for (int i=0; i<identityValues.length; i++) {
+                    filterValues = filterValues.with(identityValues[i]);
+                }
+            }
+        } else {
+            filter = Filter.getOpenFilter(getStorableType());
+            int i = 0;
+            for (; i<identityValues.length; i++) {
+                filter = filter.and(index.getProperty(i).getName(), RelOp.EQ);
+            }
+
+            filter = filter.and(index.getProperty(i).getName(),
+                                rangeEndBoundary == BoundaryType.INCLUSIVE ? RelOp.LE : RelOp.LT);
+
+            filterValues = filter.initialFilterValues();
+
+            for (i=0; i<identityValues.length; i++) {
+                filterValues = filterValues.with(identityValues[i]);
+            }
+            
+            filterValues = filterValues.with(rangeEndValue);
+        }
+
+        if (filter != null) {
+            cursor = FilteredCursor.applyFilter(filter, filterValues, cursor);
+        }
+
+        return cursor;
+    }
+
+    private List<OrderedProperty<S>> createPkPropList() {
+        return new ArrayList<OrderedProperty<S>>(mInfo.getPrimaryKey().getProperties());
+    }
+
+    private Key<S> searchKey(int tieBreaker, Object[] identityValues) {
+        S storable = prepare();
+        mKeyAssigner.setKeyValues(storable, identityValues);
+        Comparator<S> c = getSearchComparator(identityValues.length);
+        return new SearchKey<S>(tieBreaker, storable, c);
+    }
+
+    private Key<S> searchKey(int tieBreaker, Object[] identityValues, Object rangeValue) {
+        S storable = prepare();
+        mKeyAssigner.setKeyValues(storable, identityValues, rangeValue);
+        Comparator<S> c = getSearchComparator(identityValues.length + 1);
+        return new SearchKey<S>(tieBreaker, storable, c);
+    }
+
+    private Comparator<S> getSearchComparator(int propertyCount) {
+        Comparator<S> comparator = mSearchComparators[propertyCount];
+        if (comparator == null) {
+            List<OrderedProperty<S>> propList = createPkPropList().subList(0, propertyCount);
+            if (propList.size() > 0) {
+                comparator = SortedCursor.createComparator(propList);
+            } else {
+                comparator = SortedCursor.createComparator(getStorableType());
+            }
+            mSearchComparators[propertyCount] = comparator;
+        }
+        return comparator;
+    }
+
+    public SortBuffer<S> createSortBuffer() {
+        return new ArraySortBuffer<S>();
+    }
+
+    public static interface InstanceFactory {
+        Storable instantiate(DelegateSupport support);
+    }
+
+    private static class SearchKey<S extends Storable> extends Key<S> {
+        private final int mTieBreaker;
+
+        SearchKey(int tieBreaker, S storable, Comparator<S> comparator) {
+            super(storable, comparator);
+            mTieBreaker = tieBreaker;
+        }
+
+        @Override
+        protected int tieBreaker() {
+            return mTieBreaker;
+        }
+
+        @Override
+        public String toString() {
+            return super.toString() + ", tieBreaker=" + mTieBreaker;
+        }
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/MapTransaction.java b/src/main/java/com/amazon/carbonado/repo/map/MapTransaction.java
new file mode 100644
index 0000000..d2cfe87
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/MapTransaction.java
@@ -0,0 +1,240 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.util.concurrent.TimeUnit;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import com.amazon.carbonado.FetchException;
+import com.amazon.carbonado.FetchInterruptedException;
+import com.amazon.carbonado.FetchTimeoutException;
+import com.amazon.carbonado.IsolationLevel;
+import com.amazon.carbonado.PersistException;
+import com.amazon.carbonado.PersistInterruptedException;
+import com.amazon.carbonado.PersistTimeoutException;
+import com.amazon.carbonado.Storable;
+import com.amazon.carbonado.Storage;
+
+/**
+ * 
+ *
+ * @author Brian S O'Neill
+ */
+class MapTransaction {
+    private final MapTransaction mParent;
+    private final IsolationLevel mLevel;
+    private final Object mLocker;
+    private final int mLockTimeout;
+    private final TimeUnit mLockTimeoutUnit;
+
+    private Set<UpgradableLock> mUpgradeLocks;
+    private Set<UpgradableLock> mWriteLocks;
+
+    private List<Undoable> mUndoLog;
+
+    MapTransaction(MapTransaction parent, IsolationLevel level,
+                   int lockTimeout, TimeUnit lockTimeoutUnit)
+    {
+        mParent = parent;
+        mLevel = level;
+        mLocker = parent == null ? this : parent.mLocker;
+        mLockTimeout = lockTimeout;
+        mLockTimeoutUnit = lockTimeoutUnit;
+    }
+
+    void lockForUpgrade(UpgradableLock lock, boolean isForUpdate) throws FetchException {
+        if (!isForUpdate && mLevel.isAtMost(IsolationLevel.READ_COMMITTED)) {
+            doLockForUpgrade(lock);
+        } else {
+            Set<UpgradableLock> locks = mUpgradeLocks;
+            if (locks == null) {
+                mUpgradeLocks = locks = new HashSet<UpgradableLock>();
+                doLockForUpgrade(lock);
+                locks.add(lock);
+            } else if (!locks.contains(lock)) {
+                doLockForUpgrade(lock);
+                locks.add(lock);
+            }
+        }
+    }
+
+    private void doLockForUpgrade(UpgradableLock lock) throws FetchException {
+        try {
+            if (!lock.tryLockForUpgrade(mLocker, mLockTimeout, mLockTimeoutUnit)) {
+                throw new FetchTimeoutException("" + mLockTimeout + ' ' +
+                                                mLockTimeoutUnit.toString().toLowerCase());
+            }
+        } catch (InterruptedException e) {
+            throw new FetchInterruptedException(e);
+        }
+    }
+
+    void unlockFromUpgrade(UpgradableLock lock, boolean isForUpdate) {
+        if (!isForUpdate && mLevel.isAtMost(IsolationLevel.READ_COMMITTED)) {
+            lock.unlockFromUpgrade(mLocker);
+        }
+    }
+
+    void lockForWrite(UpgradableLock lock) throws PersistException {
+        Set<UpgradableLock> locks = mWriteLocks;
+        if (locks == null) {
+            mWriteLocks = locks = new HashSet<UpgradableLock>();
+            doLockForWrite(lock);
+            locks.add(lock);
+        } else if (!locks.contains(lock)) {
+            doLockForWrite(lock);
+            locks.add(lock);
+        }
+    }
+
+    private void doLockForWrite(UpgradableLock lock) throws PersistException {
+        try {
+            if (!lock.tryLockForWrite(mLocker, mLockTimeout, mLockTimeoutUnit)) {
+                throw new PersistTimeoutException("" + mLockTimeout + ' ' +
+                                                  mLockTimeoutUnit.toString().toLowerCase());
+            }
+        } catch (InterruptedException e) {
+            throw new PersistInterruptedException(e);
+        }
+    }
+
+    /**
+     * Add to undo log.
+     */
+    <S extends Storable> void inserted(final MapStorage<S> storage, final S key) {
+        addToUndoLog(new Undoable() {
+            public void undo() {
+                storage.mapRemove(key);
+            }
+        });
+    }
+
+    /**
+     * Add to undo log.
+     */
+    <S extends Storable> void updated(final MapStorage<S> storage, final S old) {
+        addToUndoLog(new Undoable() {
+            public void undo() {
+                storage.mapPut(old);
+            }
+        });
+    }
+
+    /**
+     * Add to undo log.
+     */
+    <S extends Storable> void deleted(final MapStorage<S> storage, final S old) {
+        addToUndoLog(new Undoable() {
+            public void undo() {
+                storage.mapPut(old);
+            }
+        });
+    }
+
+    void commit() {
+        MapTransaction parent = mParent;
+
+        if (parent == null) {
+            releaseLocks();
+            return;
+        }
+
+        // Pass undo log to parent.
+        if (parent.mUndoLog == null) {
+            parent.mUndoLog = mUndoLog;
+        } else if (mUndoLog != null) {
+            parent.mUndoLog.addAll(mUndoLog);
+        }
+        mUndoLog = null;
+
+        // Pass write locks to parent or release if parent already has the lock.
+        {
+            Set<UpgradableLock> locks = mWriteLocks;
+            if (locks != null) {
+                Set<UpgradableLock> parentLocks = parent.mWriteLocks;
+                if (parentLocks == null) {
+                    parent.mWriteLocks = locks;
+                } else {
+                    for (UpgradableLock lock : locks) {
+                        if (!parentLocks.add(lock)) {
+                            lock.unlockFromWrite(mLocker);
+                        }
+                    }
+                }
+                mWriteLocks = null;
+            }
+        }
+
+        // Upgrade locks can simply be released.
+        releaseUpgradeLocks();
+    }
+
+    void abort() {
+        List<Undoable> log = mUndoLog;
+        if (log != null) {
+            for (int i=log.size(); --i>=0; ) {
+                log.get(i).undo();
+            }
+        }
+        mUndoLog = null;
+
+        releaseLocks();
+    }
+
+    private void addToUndoLog(Undoable entry) {
+        List<Undoable> log = mUndoLog;
+        if (log == null) {
+            mUndoLog = log = new ArrayList<Undoable>();
+        }
+        log.add(entry);
+    }
+
+    private void releaseLocks() {
+        releaseWriteLocks();
+        releaseUpgradeLocks();
+    }
+
+    private void releaseWriteLocks() {
+        Set<UpgradableLock> locks = mWriteLocks;
+        if (locks != null) {
+            for (UpgradableLock lock : locks) {
+                lock.unlockFromWrite(mLocker);
+            }
+            mWriteLocks = null;
+        }
+    }
+
+    private void releaseUpgradeLocks() {
+        Set<UpgradableLock> locks = mUpgradeLocks;
+        if (locks != null) {
+            for (UpgradableLock lock : locks) {
+                lock.unlockFromUpgrade(mLocker);
+            }
+            mUpgradeLocks = null;
+        }
+    }
+
+    private static interface Undoable {
+        void undo();
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/MapTransactionManager.java b/src/main/java/com/amazon/carbonado/repo/map/MapTransactionManager.java
new file mode 100644
index 0000000..5598353
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/MapTransactionManager.java
@@ -0,0 +1,98 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.util.concurrent.TimeUnit;
+
+import com.amazon.carbonado.IsolationLevel;
+import com.amazon.carbonado.PersistException;
+import com.amazon.carbonado.Transaction;
+
+import com.amazon.carbonado.spi.TransactionManager;
+
+/**
+ * 
+ *
+ * @author Brian S O'Neill
+ */
+class MapTransactionManager extends TransactionManager<MapTransaction> {
+    private final int mLockTimeout;
+    private final TimeUnit mLockTimeoutUnit;
+
+    MapTransactionManager(int lockTimeout, TimeUnit lockTimeoutUnit) {
+        mLockTimeout = lockTimeout;
+        mLockTimeoutUnit = lockTimeoutUnit;
+    }
+
+    protected IsolationLevel selectIsolationLevel(Transaction parent, IsolationLevel level) {
+        if (level == null) {
+            if (parent == null) {
+                return IsolationLevel.READ_COMMITTED;
+            }
+            return parent.getIsolationLevel();
+        }
+
+        switch (level) {
+        case NONE:
+            return IsolationLevel.NONE;
+        case READ_UNCOMMITTED:
+        case READ_COMMITTED:
+            return IsolationLevel.READ_COMMITTED;
+        case REPEATABLE_READ:
+        case SERIALIZABLE:
+            return IsolationLevel.SERIALIZABLE;
+        default:
+            // Not supported.
+            return null;
+        }
+    }
+
+    protected boolean supportsForUpdate() {
+        return true;
+    }
+
+    protected MapTransaction createTxn(MapTransaction parent, IsolationLevel level)
+        throws Exception
+    {
+        if (level == IsolationLevel.NONE) {
+            return null;
+        }
+        return new MapTransaction(parent, level, mLockTimeout, mLockTimeoutUnit);
+    }
+
+    @Override
+    protected MapTransaction createTxn(MapTransaction parent, IsolationLevel level,
+                                       int timeout, TimeUnit unit)
+        throws Exception
+    {
+        if (level == IsolationLevel.NONE) {
+            return null;
+        }
+        return new MapTransaction(parent, level, timeout, unit);
+    }
+
+    protected boolean commitTxn(MapTransaction txn) throws PersistException {
+        txn.commit();
+        return false;
+    }
+
+    protected void abortTxn(MapTransaction txn) throws PersistException {
+        txn.abort();
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/UpgradableLock.java b/src/main/java/com/amazon/carbonado/repo/map/UpgradableLock.java
new file mode 100644
index 0000000..9862791
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/UpgradableLock.java
@@ -0,0 +1,1161 @@
+/*
+ * Copyright 2007 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.amazon.carbonado.repo.map;
+
+import java.util.concurrent.TimeUnit;
+
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+import java.util.concurrent.locks.LockSupport;
+
+/**
+ * Partially reentrant, upgradable read/write lock. Up to 1,073,741,824 read
+ * locks can be held. Upgraders and writers may re-enter the lock up to
+ * 2,147,483,648 times. Attempts by readers to re-enter the lock is not
+ * detected and is deadlock prone, unless locker already holds an upgrade or
+ * write lock. Subclasses can support full reentrancy by overriding the
+ * protected read lock adjust and hold check methods.
+ *
+ * <p>This lock implementation differs from the usual Java lock with respect to
+ * lock ownership. Locks are not owned by threads, but by arbitrary locker
+ * objects. A thread which attempts to acquire an upgrade or write lock twice
+ * with different locker objects will deadlock on the second attempt.
+ *
+ * <p>As is typical of read/write lock implementations, a read lock blocks
+ * waiting writers, but it doesn't block other readers. A write lock is
+ * exclusive and can be held by at most one locker. Attempting to acquire a
+ * write lock while a read lock is held by the same locker is inherently
+ * deadlock prone, and some read/write lock implementations will always
+ * deadlock.
+ *
+ * <p>An upgrade lock allows a read lock to be safely upgraded to a write
+ * lock. Instead of acquiring a read lock, an upgrade lock is acquired. This
+ * acts like a shared read lock in that readers are not blocked, but it also
+ * acts like an exclusive write lock -- writers and upgraders are blocked. With
+ * an upgrade lock held, the locker may acquire a write lock without deadlock.
+ *
+ * <pre>
+ * Locks held    Locks safely           Locks acquirable
+ * by owner      acquirable by owner    by other lockers
+ * --------------------------------------------------
+ *   - - -         R U W                  R U W
+ *   R - -         - - -                  R U -
+ *   R U -         - U -                  R - -
+ *   - U -         R U W                  R - -
+ *   - U W         R U W                  - - -
+ *   R U W         R U W                  - - -
+ *   R - W         R U W                  - - -
+ *   - - W         R U W                  - - -
+ * </pre>
+ *
+ * @author Brian S O'Neill
+ * @param <L> Locker type
+ */
+class UpgradableLock<L> {
+    // Design note: This class borrows heavily from AbstractQueuedSynchronizer.
+    // Consult that class for understanding the locking mechanics.
+
+    private static enum Result {
+        /** Lock acquisition failed */
+        FAILED,
+        /** Lock has just been acquired by locker and can be safely released later */
+        ACQUIRED,
+        /** Lock is already owned by locker and should not be released more than once */
+        OWNED
+    }
+
+    private static final AtomicReferenceFieldUpdater<UpgradableLock, Node> cRWHeadRef =
+        AtomicReferenceFieldUpdater.newUpdater
+        (UpgradableLock.class, Node.class, "mRWHead");
+
+    private static final AtomicReferenceFieldUpdater<UpgradableLock, Node> cRWTailRef =
+        AtomicReferenceFieldUpdater.newUpdater
+        (UpgradableLock.class, Node.class, "mRWTail");
+
+    private static final AtomicReferenceFieldUpdater<UpgradableLock, Node> cUHeadRef =
+        AtomicReferenceFieldUpdater.newUpdater
+        (UpgradableLock.class, Node.class, "mUHead");
+
+    private static final AtomicReferenceFieldUpdater<UpgradableLock, Node> cUTailRef =
+        AtomicReferenceFieldUpdater.newUpdater
+        (UpgradableLock.class, Node.class, "mUTail");
+
+    private static final AtomicIntegerFieldUpdater<UpgradableLock> cStateRef =
+        AtomicIntegerFieldUpdater.newUpdater
+        (UpgradableLock.class, "mState");
+
+    // State mask bits for held locks. Read lock count is stored in lower 30 bits of state.
+    private static final int LOCK_STATE_UPGRADE = 0x40000000;
+    // Write state must be this value in order for quick sign check to work.
+    private static final int LOCK_STATE_WRITE = 0x80000000;
+
+    private static final int LOCK_STATE_MASK = LOCK_STATE_UPGRADE | LOCK_STATE_WRITE;
+
+    /**
+     * The number of nanoseconds for which it is faster to spin
+     * rather than to use timed park. A rough estimate suffices
+     * to improve responsiveness with very short timeouts.
+     */
+    private static final long SPIN_FOR_TIMEOUT_THRESHOLD = 1000L;
+
+    // Head of read-write queue.
+    private transient volatile Node mRWHead;
+
+    // Tail of read-write queue.
+    private transient volatile Node mRWTail;
+
+    // Head of write upgrade queue.
+    private transient volatile Node mUHead;
+
+    // Tail of write upgrade queue.
+    private transient volatile Node mUTail;
+
+    private transient volatile int mState;
+
+    // Owner holds an upgradable lock and possibly a write lock too.
+    private transient L mOwner;
+
+    // Counts number of times that owner has entered an upgradable or write lock.
+    private transient int mUpgradeCount;
+    private transient int mWriteCount;
+
+    public UpgradableLock() {
+    }
+
+    /**
+     * Acquire a shared read lock, possibly blocking indefinitely.
+     *
+     * @param locker object which might be write or upgrade lock owner
+     */
+    public final void lockForRead(L locker) {
+        if (!tryLockForRead(locker)) {
+            lockForReadQueued(locker, addReadWaiter());
+        }
+    }
+
+    /**
+     * Acquire a shared read lock, possibly blocking until interrupted.
+     *
+     * @param locker object which might be write or upgrade lock owner
+     */
+    public final void lockForReadInterruptibly(L locker) throws InterruptedException {
+        if (Thread.interrupted()) {
+            throw new InterruptedException();
+        }
+        if (!tryLockForRead(locker)) {
+            lockForReadQueuedInterruptibly(locker, addReadWaiter());
+        }
+    }
+
+    /**
+     * Attempt to immediately acquire a shared read lock.
+     *
+     * @param locker object which might be write or upgrade lock owner
+     * @return true if acquired
+     */
+    public final boolean tryLockForRead(L locker) {
+        int state = mState;
+        if (state >= 0) { // no write lock is held
+            if (isReadWriteFirst() || isReadLockHeld(locker)) {
+                do {
+                    if (incrementReadLocks(state)) {
+                        adjustReadLockCount(locker, 1);
+                        return true;
+                    }
+                    // keep looping on CAS failure if a reader or upgrader mucked with the state
+                } while ((state = mState) >= 0);
+            }
+        } else if (mOwner == locker) {
+            // keep looping on CAS failure if a reader or upgrader mucked with the state
+            while (!incrementReadLocks(state)) {
+                state = mState;
+            }
+            adjustReadLockCount(locker, 1);
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * Attempt to acquire a shared read lock, waiting a maximum amount of
+     * time.
+     *
+     * @param locker object which might be write or upgrade lock owner
+     * @return true if acquired
+     */
+    public final boolean tryLockForRead(L locker, long timeout, TimeUnit unit)
+        throws InterruptedException
+    {
+        if (Thread.interrupted()) {
+            throw new InterruptedException();
+        }
+        if (!tryLockForRead(locker)) {
+            return lockForReadQueuedInterruptibly(locker, addReadWaiter(), unit.toNanos(timeout));
+        }
+        return true;
+    }
+
+    /**
+     * Release a previously acquired read lock.
+     */
+    public final void unlockFromRead(L locker) {
+        adjustReadLockCount(locker, -1);
+
+        int readLocks;
+        while ((readLocks = decrementReadLocks(mState)) < 0) {}
+
+        if (readLocks == 0) {
+            Node h = mRWHead;
+            if (h != null && h.mWaitStatus != 0) {
+                unparkReadWriteSuccessor(h);
+            }
+        }
+    }
+
+    /**
+     * Acquire an upgrade lock, possibly blocking indefinitely.
+     *
+     * @param locker object trying to become lock owner
+     * @return true if acquired
+     */
+    public final boolean lockForUpgrade(L locker) {
+        return lockForUpgrade_(locker) != Result.FAILED;
+    }
+
+    /**
+     * Acquire an upgrade lock, possibly blocking indefinitely.
+     *
+     * @param locker object trying to become lock owner
+     * @return ACQUIRED or OWNED
+     */
+    private final Result lockForUpgrade_(L locker) {
+        Result result;
+        if ((result = tryLockForUpgrade_(locker)) == Result.FAILED) {
+            result = lockForUpgradeQueued(locker, addUpgradeWaiter());
+        }
+        return result;
+    }
+
+    /**
+     * Acquire an upgrade lock, possibly blocking until interrupted.
+     *
+     * @param locker object trying to become lock owner
+     * @return true if acquired
+     */
+    public final boolean lockForUpgradeInterruptibly(L locker) throws InterruptedException {
+        return lockForUpgradeInterruptibly_(locker) != Result.FAILED;
+    }
+
+    /**
+     * Acquire an upgrade lock, possibly blocking until interrupted.
+     *
+     * @param locker object trying to become lock owner
+     * @return ACQUIRED or OWNED
+     */
+    private final Result lockForUpgradeInterruptibly_(L locker) throws InterruptedException {
+        if (Thread.interrupted()) {
+            throw new InterruptedException();
+        }
+        Result result;
+        if ((result = tryLockForUpgrade_(locker)) == Result.FAILED) {
+            result = lockForUpgradeQueuedInterruptibly(locker, addUpgradeWaiter());
+        }
+        return result;
+    }
+
+    /**
+     * Attempt to immediately acquire an upgrade lock.
+     *
+     * @param locker object trying to become lock owner
+     * @return true if acquired
+     */
+    public final boolean tryLockForUpgrade(L locker) {
+        return tryLockForUpgrade_(locker) != Result.FAILED;
+    }
+
+    /**
+     * Attempt to immediately acquire an upgrade lock.
+     *
+     * @param locker object trying to become lock owner
+     * @return FAILED, ACQUIRED or OWNED
+     */
+    private final Result tryLockForUpgrade_(L locker) {
+        int state = mState;
+        if ((state & LOCK_STATE_MASK) == 0) { // no write or upgrade lock is held
+            if (isUpgradeFirst()) {
+                do {
+                    if (setUpgradeLock(state)) {
+                        mOwner = locker;
+                        incrementUpgradeCount();
+                        return Result.ACQUIRED;
+                    }
+                    // keep looping on CAS failure if a reader mucked with the state
+                } while (((state = mState) & LOCK_STATE_MASK) == 0);
+            }
+        } else if (mOwner == locker) {
+            incrementUpgradeCount();
+            return Result.OWNED;
+        }
+        return Result.FAILED;
+    }
+
+    /**
+     * Attempt to acquire an upgrade lock, waiting a maximum amount of time.
+     *
+     * @param locker object trying to become lock owner
+     * @return true if acquired
+     */
+    public final boolean tryLockForUpgrade(L locker, long timeout, TimeUnit unit)
+        throws InterruptedException
+    {
+        return tryLockForUpgrade_(locker, timeout, unit) != Result.FAILED;
+    }
+
+    /**
+     * Attempt to acquire an upgrade lock, waiting a maximum amount of time.
+     *
+     * @param locker object trying to become lock owner
+     * @return FAILED, ACQUIRED or OWNED
+     */
+    private final Result tryLockForUpgrade_(L locker, long timeout, TimeUnit unit)
+        throws InterruptedException
+    {
+        if (Thread.interrupted()) {
+            throw new InterruptedException();
+        }
+        Result result;
+        if ((result = tryLockForUpgrade_(locker)) == Result.FAILED) {
+            result = lockForUpgradeQueuedInterruptibly(locker, addUpgradeWaiter(),
+                                                       unit.toNanos(timeout));
+        }
+        return result;
+    }
+
+    /**
+     * Release a previously acquired upgrade lock.
+     */
+    public final void unlockFromUpgrade(L locker) {
+        int upgradeCount = mUpgradeCount - 1;
+        if (upgradeCount < 0) {
+            throw new IllegalMonitorStateException("Too many upgrade locks released");
+        }
+        if (upgradeCount == 0 && mWriteCount > 0) {
+            // Don't release last upgrade lock and switch write lock to
+            // automatic upgrade mode.
+            clearUpgradeLock(mState);
+            return;
+        }
+        mUpgradeCount = upgradeCount;
+        if (upgradeCount > 0) {
+            return;
+        }
+
+        mOwner = null;
+
+        // keep looping on CAS failure if reader mucked with state
+        while (!clearUpgradeLock(mState)) {}
+
+        Node h = mUHead;
+        if (h != null && h.mWaitStatus != 0) {
+            unparkUpgradeSuccessor(h);
+        }
+    }
+
+    /**
+     * Acquire an exclusive write lock, possibly blocking indefinitely.
+     *
+     * @param locker object trying to become lock owner
+     */
+    public final void lockForWrite(L locker) {
+        Result writeResult;
+        if (!tryLockForWrite(locker)) {
+            Result upgradeResult = lockForUpgrade_(locker);
+            if (!tryLockForWrite(locker)) {
+                lockForWriteQueued(locker, addWriteWaiter());
+            }
+            if (upgradeResult == Result.ACQUIRED) {
+                // clear upgrade state bit to indicate automatic upgrade
+                while (!clearUpgradeLock(mState)) {}
+            } else {
+                // undo automatic upgrade count increment
+                mUpgradeCount--;
+            }
+        }
+    }
+
+    /**
+     * Acquire an exclusive write lock, possibly blocking until interrupted.
+     *
+     * @param locker object trying to become lock owner
+     */
+    public final void lockForWriteInterruptibly(L locker) throws InterruptedException {
+        if (Thread.interrupted()) {
+            throw new InterruptedException();
+        }
+        if (!tryLockForWrite(locker)) {
+            Result upgradeResult = lockForUpgradeInterruptibly_(locker);
+            if (!tryLockForWrite(locker)) {
+                lockForWriteQueuedInterruptibly(locker, addWriteWaiter());
+            }
+            if (upgradeResult == Result.ACQUIRED) {
+                // clear upgrade state bit to indicate automatic upgrade
+                while (!clearUpgradeLock(mState)) {}
+            } else {
+                // undo automatic upgrade count increment
+                mUpgradeCount--;
+            }
+        }
+    }
+
+    /**
+     * Attempt to immediately acquire an exclusive lock.
+     *
+     * @param locker object trying to become lock owner
+     * @return true if acquired
+     */
+    public final boolean tryLockForWrite(L locker) {
+        int state = mState;
+        if (state == 0) {
+            // no locks are held
+            if (isUpgradeOrReadWriteFirst() && setWriteLock(state)) {
+                // keep upgrade state bit clear to indicate automatic upgrade
+                mOwner = locker;
+                incrementUpgradeCount();
+                incrementWriteCount();
+                return true;
+            }
+        } else if (state == LOCK_STATE_UPGRADE) {
+            // only upgrade lock is held; upgrade to full write lock
+            if (mOwner == locker && setWriteLock(state)) {
+                incrementWriteCount();
+                return true;
+            }
+        } else if (state < 0) {
+            // write lock is held, and upgrade lock might be held too
+            if (mOwner == locker) {
+                incrementWriteCount();
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Attempt to acquire an exclusive lock, waiting a maximum amount of time.
+     *
+     * @param locker object trying to become lock owner
+     * @return true if acquired
+     */
+    public final boolean tryLockForWrite(L locker, long timeout, TimeUnit unit)
+        throws InterruptedException
+    {
+        if (Thread.interrupted()) {
+            throw new InterruptedException();
+        }
+        if (!tryLockForWrite(locker)) {
+            return lockForWriteQueuedInterruptibly(locker, addWriteWaiter(),
+                                                   unit.toNanos(timeout));
+        }
+        return true;
+    }
+
+    /**
+     * Release a previously acquired write lock.
+     */
+    public final void unlockFromWrite(L locker) {
+        int writeCount = mWriteCount - 1;
+        if (writeCount < 0) {
+            throw new IllegalMonitorStateException("Too many write locks released");
+        }
+        mWriteCount = writeCount;
+        if (writeCount > 0) {
+            return;
+        }
+
+        // copy original state to check if upgrade lock was automatic
+        final int state = mState;
+
+        // make sure upgrade lock is still held after releasing write lock
+        mState = LOCK_STATE_UPGRADE;
+
+        Node h = mRWHead;
+        if (h != null && h.mWaitStatus != 0) {
+            unparkReadWriteSuccessor(h);
+        }
+
+        if (state == LOCK_STATE_WRITE) {
+            // upgrade owner was automatically set, so automatically clear it
+            unlockFromUpgrade(locker);
+        }
+    }
+
+    public String toString() {
+        int state = mState;
+        int readLocks = state & ~LOCK_STATE_MASK;
+        int upgradeLocks = mUpgradeCount;
+        int writeLocks = mWriteCount;
+
+        return super.toString()
+            + "[Read locks = " + readLocks
+            + ", Upgrade locks = " + upgradeLocks
+            + ", Write locks = " + writeLocks
+            + ", Owner = " + mOwner
+            + ']';
+    }
+
+    /**
+     * Add or subtract to the count of read locks held for the given
+     * locker. Default implementation does nothing, and so read locks are not
+     * reentrant.
+     *
+     * @throws IllegalMonitorStateException if count overflows or underflows
+     */
+    protected void adjustReadLockCount(L locker, int amount) {
+    }
+
+    /**
+     * Default implementation does nothing and always returns false, and so
+     * read locks are not reentrant. Overridden implementation may choose to
+     * always returns true, in which case read lock requests can starve upgrade
+     * and write lock requests.
+     */
+    protected boolean isReadLockHeld(L locker) {
+        return false;
+    }
+
+    private Node enqForReadWrite(final Node node) {
+        for (;;) {
+            Node t = mRWTail;
+            if (t == null) { // Must initialize
+                Node h = new Node(); // Dummy header
+                h.mNext = node;
+                node.mPrev = h;
+                if (cRWHeadRef.compareAndSet(this, null, h)) {
+                    mRWTail = node;
+                    return h;
+                }
+            } else {
+                node.mPrev = t;
+                if (cRWTailRef.compareAndSet(this, t, node)) {
+                    t.mNext = node;
+                    return t;
+                }
+            }
+        }
+    }
+
+    private Node enqForUpgrade(final Node node) {
+        for (;;) {
+            Node t = mUTail;
+            if (t == null) { // Must initialize
+                Node h = new Node(); // Dummy header
+                h.mNext = node;
+                node.mPrev = h;
+                if (cUHeadRef.compareAndSet(this, null, h)) {
+                    mUTail = node;
+                    return h;
+                }
+            } else {
+                node.mPrev = t;
+                if (cUTailRef.compareAndSet(this, t, node)) {
+                    t.mNext = node;
+                    return t;
+                }
+            }
+        }
+    }
+
+    private Node addReadWaiter() {
+        return addReadWriteWaiter(true);
+    }
+
+    private Node addWriteWaiter() {
+        return addReadWriteWaiter(false);
+    }
+
+    private Node addReadWriteWaiter(boolean shared) {
+        Node node = new Node(Thread.currentThread(), shared);
+        // Try the fast path of enq; backup to full enq on failure
+        Node pred = mRWTail;
+        if (pred != null) {
+            node.mPrev = pred;
+            if (cRWTailRef.compareAndSet(this, pred, node)) {
+                pred.mNext = node;
+                return node;
+            }
+        }
+        enqForReadWrite(node);
+        return node;
+    }
+
+    private Node addUpgradeWaiter() {
+        Node node = new Node(Thread.currentThread(), false);
+        // Try the fast path of enq; backup to full enq on failure
+        Node pred = mUTail;
+        if (pred != null) {
+            node.mPrev = pred;
+            if (cUTailRef.compareAndSet(this, pred, node)) {
+                pred.mNext = node;
+                return node;
+            }
+        }
+        enqForUpgrade(node);
+        return node;
+    }
+
+    private void setReadWriteHead(Node node) {
+        mRWHead = node;
+        node.mThread = null;
+        node.mPrev = null;
+    }
+
+    private void setUpgradeHead(Node node) {
+        mUHead = node;
+        node.mThread = null;
+        node.mPrev = null;
+    }
+
+    private void unparkReadWriteSuccessor(Node node) {
+        Node.cWaitStatusRef.compareAndSet(node, Node.SIGNAL, 0);
+
+        Node s = node.mNext;
+        if (s == null || s.mWaitStatus > 0) {
+            s = null;
+            for (Node t = mRWTail; t != null && t != node; t = t.mPrev) {
+                if (t.mWaitStatus <= 0) {
+                    s = t;
+                }
+            }
+        }
+        if (s != null) {
+            LockSupport.unpark(s.mThread);
+        }
+    }
+
+    private void unparkUpgradeSuccessor(Node node) {
+        Node.cWaitStatusRef.compareAndSet(node, Node.SIGNAL, 0);
+
+        Node s = node.mNext;
+        if (s == null || s.mWaitStatus > 0) {
+            s = null;
+            for (Node t = mUTail; t != null && t != node; t = t.mPrev) {
+                if (t.mWaitStatus <= 0) {
+                    s = t;
+                }
+            }
+        }
+        if (s != null) {
+            LockSupport.unpark(s.mThread);
+        }
+    }
+
+    private void setReadWriteHeadAndPropagate(Node node) {
+        setReadWriteHead(node);
+        if (node.mWaitStatus != 0) {
+            Node s = node.mNext;
+            if (s == null || s.mShared) {
+                unparkReadWriteSuccessor(node);
+            }
+        }
+    }
+
+    private void cancelAcquireReadWrite(Node node) {
+        if (node != null) {
+            node.mThread = null;
+            node.mWaitStatus = Node.CANCELLED;
+            unparkReadWriteSuccessor(node);
+        }
+    }
+
+    private void cancelAcquireUpgrade(Node node) {
+        if (node != null) {
+            node.mThread = null;
+            node.mWaitStatus = Node.CANCELLED;
+            unparkUpgradeSuccessor(node);
+        }
+    }
+
+    private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) {
+        int s = pred.mWaitStatus;
+        if (s < 0) {
+            return true;
+        }
+        if (s > 0) {
+            node.mPrev = pred.mPrev;
+        } else {
+            Node.cWaitStatusRef.compareAndSet(pred, 0, Node.SIGNAL);
+        }
+        return false;
+    }
+
+    private static void selfInterrupt() {
+        Thread.currentThread().interrupt();
+    }
+
+    private final boolean parkAndCheckInterrupt() {
+        LockSupport.park(this);
+        return Thread.interrupted();
+    }
+
+    /**
+     * @return ACQUIRED or OWNED
+     */
+    private final Result lockForUpgradeQueued(L locker, final Node node) {
+        try {
+            boolean interrupted = false;
+            for (;;) {
+                final Node p = node.predecessor();
+                Result result;
+                if (p == mUHead && (result = tryLockForUpgrade_(locker)) != Result.FAILED) {
+                    setUpgradeHead(node);
+                    p.mNext = null; // help GC
+                    if (interrupted) {
+                        selfInterrupt();
+                    }
+                    return result;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) {
+                    interrupted = true;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireUpgrade(node);
+            throw e;
+        }
+    }
+
+    /**
+     * @return ACQUIRED or OWNED
+     */
+    private final Result lockForUpgradeQueuedInterruptibly(L locker, final Node node)
+        throws InterruptedException
+    {
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                Result result;
+                if (p == mUHead && (result = tryLockForUpgrade_(locker)) != Result.FAILED) {
+                    setUpgradeHead(node);
+                    p.mNext = null; // help GC
+                    return result;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) {
+                    break;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireUpgrade(node);
+            throw e;
+        }
+        // Arrive here only if interrupted
+        cancelAcquireUpgrade(node);
+        throw new InterruptedException();
+    }
+
+    /**
+     * @return FAILED, ACQUIRED or OWNED
+     */
+    private final Result lockForUpgradeQueuedInterruptibly(L locker, final Node node,
+                                                           long nanosTimeout)
+        throws InterruptedException
+    {
+        long lastTime = System.nanoTime();
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                Result result;
+                if (p == mUHead && (result = tryLockForUpgrade_(locker)) != Result.FAILED) {
+                    setUpgradeHead(node);
+                    p.mNext = null; // help GC
+                    return result;
+                }
+                if (nanosTimeout <= 0) {
+                    cancelAcquireUpgrade(node);
+                    return Result.FAILED;
+                }
+                if (nanosTimeout > SPIN_FOR_TIMEOUT_THRESHOLD
+                    && shouldParkAfterFailedAcquire(p, node))
+                {
+                    LockSupport.parkNanos(this, nanosTimeout);
+                }
+                long now = System.nanoTime();
+                nanosTimeout -= now - lastTime;
+                lastTime = now;
+                if (Thread.interrupted()) {
+                    break;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireUpgrade(node);
+            throw e;
+        }
+        // Arrive here only if interrupted
+        cancelAcquireUpgrade(node);
+        throw new InterruptedException();
+    }
+
+    private final void lockForReadQueued(L locker, final Node node) {
+        try {
+            boolean interrupted = false;
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == mRWHead && tryLockForRead(locker)) {
+                    setReadWriteHeadAndPropagate(node);
+                    p.mNext = null; // help GC
+                    if (interrupted) {
+                        selfInterrupt();
+                    }
+                    return;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) {
+                    interrupted = true;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireReadWrite(node);
+            throw e;
+        }
+    }
+
+    private final void lockForReadQueuedInterruptibly(L locker, final Node node)
+        throws InterruptedException
+    {
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == mRWHead && tryLockForRead(locker)) {
+                    setReadWriteHeadAndPropagate(node);
+                    p.mNext = null; // help GC
+                    return;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) {
+                    break;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireReadWrite(node);
+            throw e;
+        }
+        // Arrive here only if interrupted
+        cancelAcquireReadWrite(node);
+        throw new InterruptedException();
+    }
+
+    /**
+     * @return true if acquired
+     */
+    private final boolean lockForReadQueuedInterruptibly(L locker, final Node node,
+                                                         long nanosTimeout)
+        throws InterruptedException
+    {
+        long lastTime = System.nanoTime();
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == mRWHead && tryLockForRead(locker)) {
+                    setReadWriteHeadAndPropagate(node);
+                    p.mNext = null; // help GC
+                    return true;
+                }
+                if (nanosTimeout <= 0) {
+                    cancelAcquireReadWrite(node);
+                    return false;
+                }
+                if (nanosTimeout > SPIN_FOR_TIMEOUT_THRESHOLD
+                    && shouldParkAfterFailedAcquire(p, node))
+                {
+                    LockSupport.parkNanos(this, nanosTimeout);
+                }
+                long now = System.nanoTime();
+                nanosTimeout -= now - lastTime;
+                lastTime = now;
+                if (Thread.interrupted()) {
+                    break;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireReadWrite(node);
+            throw e;
+        }
+        // Arrive here only if interrupted
+        cancelAcquireReadWrite(node);
+        throw new InterruptedException();
+    }
+
+    private final void lockForWriteQueued(L locker, final Node node) {
+        try {
+            boolean interrupted = false;
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == mRWHead && tryLockForWrite(locker)) {
+                    setReadWriteHead(node);
+                    p.mNext = null; // help GC
+                    if (interrupted) {
+                        selfInterrupt();
+                    }
+                    return;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) {
+                    interrupted = true;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireReadWrite(node);
+            throw e;
+        }
+    }
+
+    private final void lockForWriteQueuedInterruptibly(L locker, final Node node)
+        throws InterruptedException
+    {
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == mRWHead && tryLockForWrite(locker)) {
+                    setReadWriteHead(node);
+                    p.mNext = null; // help GC
+                    return;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) {
+                    break;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireReadWrite(node);
+            throw e;
+        }
+        // Arrive here only if interrupted
+        cancelAcquireReadWrite(node);
+        throw new InterruptedException();
+    }
+
+    /**
+     * @return true if acquired
+     */
+    private final boolean lockForWriteQueuedInterruptibly(L locker, final Node node,
+                                                          long nanosTimeout)
+        throws InterruptedException
+    {
+        long lastTime = System.nanoTime();
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == mRWHead && tryLockForWrite(locker)) {
+                    setReadWriteHead(node);
+                    p.mNext = null; // help GC
+                    return true;
+                }
+                if (nanosTimeout <= 0) {
+                    cancelAcquireReadWrite(node);
+                    return false;
+                }
+                if (nanosTimeout > SPIN_FOR_TIMEOUT_THRESHOLD
+                    && shouldParkAfterFailedAcquire(p, node))
+                {
+                    LockSupport.parkNanos(this, nanosTimeout);
+                }
+                long now = System.nanoTime();
+                nanosTimeout -= now - lastTime;
+                lastTime = now;
+                if (Thread.interrupted()) {
+                    break;
+                }
+            }
+        } catch (RuntimeException e) {
+            cancelAcquireReadWrite(node);
+            throw e;
+        }
+        // Arrive here only if interrupted
+        cancelAcquireReadWrite(node);
+        throw new InterruptedException();
+    }
+
+    private final boolean isReadWriteFirst() {
+        Node h;
+        if ((h = mRWHead) == null) {
+            return true;
+        }
+        Thread current = Thread.currentThread();
+        Node s;
+        return ((s = h.mNext) != null && s.mThread == current) || fullIsReadWriteFirst(current);
+    }
+
+    private final boolean fullIsReadWriteFirst(Thread current) {
+        Node h, s;
+        Thread firstThread = null;
+        if (((h = mRWHead) != null && (s = h.mNext) != null &&
+             s.mPrev == mRWHead && (firstThread = s.mThread) != null))
+        {
+            return firstThread == current;
+        }
+        Node t = mRWTail;
+        while (t != null && t != mRWHead) {
+            Thread tt = t.mThread;
+            if (tt != null) {
+                firstThread = tt;
+            }
+            t = t.mPrev;
+        }
+        return firstThread == current || firstThread == null;
+    }
+
+    private final boolean isUpgradeFirst() {
+        Node h;
+        if ((h = mUHead) == null) {
+            return true;
+        }
+        Thread current = Thread.currentThread();
+        Node s;
+        return ((s = h.mNext) != null && s.mThread == current) || fullIsUpgradeFirst(current);
+    }
+
+    private final boolean fullIsUpgradeFirst(Thread current) {
+        Node h, s;
+        Thread firstThread = null;
+        if (((h = mUHead) != null && (s = h.mNext) != null &&
+             s.mPrev == mUHead && (firstThread = s.mThread) != null))
+        {
+            return firstThread == current;
+        }
+        Node t = mUTail;
+        while (t != null && t != mUHead) {
+            Thread tt = t.mThread;
+            if (tt != null) {
+                firstThread = tt;
+            }
+            t = t.mPrev;
+        }
+        return firstThread == current || firstThread == null;
+    }
+
+    private final boolean isUpgradeOrReadWriteFirst() {
+        Node uh, rwh;
+        if ((uh = mUHead) == null || (rwh = mRWHead) == null) {
+            return true;
+        }
+        Thread current = Thread.currentThread();
+        Node us, rws;
+        return ((us = uh.mNext) != null && us.mThread == current)
+            || ((rws = rwh.mNext) != null && rws.mThread == current)
+            || fullIsUpgradeFirst(current)
+            || fullIsReadWriteFirst(current);
+    }
+
+    /**
+     * @return false if state changed
+     */
+    private boolean incrementReadLocks(int state) {
+        int readLocks = (state & ~LOCK_STATE_MASK) + 1;
+        if (readLocks == LOCK_STATE_MASK) {
+            throw new IllegalMonitorStateException("Maximum read lock count exceeded");
+        }
+        return cStateRef.compareAndSet(this, state, state & LOCK_STATE_MASK | readLocks);
+    }
+
+    /**
+     * @return number of remaining read locks or negative if concurrent
+     * modification prevented operation
+     */
+    private int decrementReadLocks(int state) {
+        int readLocks = (state & ~LOCK_STATE_MASK) - 1;
+        if (readLocks < 0) {
+            throw new IllegalMonitorStateException("Too many read locks released");
+        }
+        if (cStateRef.compareAndSet(this, state, state & LOCK_STATE_MASK | readLocks)) {
+            return readLocks;
+        }
+        return -1;
+    }
+
+    /**
+     * @return false if concurrent modification prevented operation
+     */
+    private boolean setUpgradeLock(int state) {
+        return cStateRef.compareAndSet(this, state, state | LOCK_STATE_UPGRADE);
+    }
+
+    /**
+     * @return false if concurrent modification prevented operation
+     */
+    private boolean clearUpgradeLock(int state) {
+        return cStateRef.compareAndSet(this, state, state & ~LOCK_STATE_UPGRADE);
+    }
+
+    private void incrementUpgradeCount() {
+        int upgradeCount = mUpgradeCount + 1;
+        if (upgradeCount < 0) {
+            throw new IllegalMonitorStateException("Maximum upgrade lock count exceeded");
+        }
+        mUpgradeCount = upgradeCount;
+    }
+
+    /**
+     * @return false if concurrent modification prevented operation
+     */
+    private boolean setWriteLock(int state) {
+        return cStateRef.compareAndSet(this, state, state | LOCK_STATE_WRITE);
+    }
+
+    private void incrementWriteCount() {
+        int writeCount = mWriteCount + 1;
+        if (writeCount < 0) {
+            throw new IllegalMonitorStateException("Maximum write lock count exceeded");
+        }
+        mWriteCount = writeCount;
+    }
+
+    /**
+     * Node class ripped off from AbstractQueuedSynchronizer and modified
+     * slightly. Read the comments in that class for better understanding.
+     */
+    static final class Node {
+        static final AtomicIntegerFieldUpdater<Node> cWaitStatusRef =
+            AtomicIntegerFieldUpdater.newUpdater(Node.class, "mWaitStatus");
+
+        static final int CANCELLED =  1;
+        static final int SIGNAL    = -1;
+
+        volatile int mWaitStatus;
+        volatile Node mPrev;
+        volatile Node mNext;
+        volatile Thread mThread;
+
+        final boolean mShared;
+
+        // Used to establish initial head
+        Node() {
+            mShared = false;
+        }
+
+        Node(Thread thread, boolean shared) {
+            mThread = thread;
+            mShared = shared;
+        }
+
+        final Node predecessor() throws NullPointerException {
+            Node p = mPrev;
+            if (p == null) {
+                throw new NullPointerException();
+            } else {
+                return p;
+            }
+        }
+    }
+}
diff --git a/src/main/java/com/amazon/carbonado/repo/map/package-info.java b/src/main/java/com/amazon/carbonado/repo/map/package-info.java
new file mode 100644
index 0000000..b386251
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/repo/map/package-info.java
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2008 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Volatile repository implementation backed by a concurrent map.
+ *
+ * @see com.amazon.carbonado.repo.map.MapRepositoryBuilder
+ */
+package com.amazon.carbonado.repo.map;
-- 
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