Added option for index access to fetch ahead to reduce likelihood of deadlocks.

2 files changed, 86 insertions, 1 deletions

diff --git a/src/main/java/com/amazon/carbonado/cursor/FetchAheadCursor.java b/src/main/java/com/amazon/carbonado/cursor/FetchAheadCursor.java
new file mode 100644
index 0000000..743364d
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/cursor/FetchAheadCursor.java
@@ -0,0 +1,73 @@
+/*

+ * Copyright 2012 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.cursor;

+

+import java.util.ArrayDeque;

+import java.util.NoSuchElementException;

+import java.util.Queue;

+

+import com.amazon.carbonado.Cursor;

+import com.amazon.carbonado.FetchException;

+

+/**

+ * Cursor implementation which fetches records in advance, in order to release locks.

+ *

+ * @author Brian S O'Neill

+ */

+public class FetchAheadCursor<S> extends AbstractCursor<S> {

+    private final Cursor<S> mSource;

+    private final int mFetchAhead;

+    private final Queue<Object> mQueue;

+

+    /**

+     * @param fetchAhead how much to fetch ahead from source

+     */

+    public FetchAheadCursor(Cursor<S> source, int fetchAhead) {

+        mSource = source;

+        mFetchAhead = fetchAhead;

+        mQueue = new ArrayDeque<Object>(fetchAhead + 1);

+    }

+

+    public void close() throws FetchException {

+        mQueue.clear();

+        mSource.close();

+    }

+

+    public boolean hasNext() throws FetchException {

+        while (mQueue.size() <= mFetchAhead && mSource.hasNext()) {

+            try {

+                mQueue.add(mSource.next());

+            } catch (FetchException e) {

+                mQueue.add(e);

+            }

+        }

+        return !mQueue.isEmpty();

+    }

+

+    public S next() throws FetchException {

+        if (!hasNext()) {

+            throw new NoSuchElementException();

+        }

+        Object next = mQueue.remove();

+        if (next instanceof FetchException) {

+            throw (FetchException) next;

+        }

+        return (S) next;

+    }

+}

diff --git a/src/main/java/com/amazon/carbonado/repo/indexed/IndexedCursor.java b/src/main/java/com/amazon/carbonado/repo/indexed/IndexedCursor.java
index bce6975..04eb478 100644
--- a/src/main/java/com/amazon/carbonado/repo/indexed/IndexedCursor.java
+++ b/src/main/java/com/amazon/carbonado/repo/indexed/IndexedCursor.java
@@ -32,6 +32,7 @@ import com.amazon.carbonado.Storage;
 import com.amazon.carbonado.Transaction;

 

 import com.amazon.carbonado.cursor.AbstractCursor;

+import com.amazon.carbonado.cursor.FetchAheadCursor;

 

 import com.amazon.carbonado.spi.RepairExecutor;

 

@@ -44,6 +45,13 @@ import com.amazon.carbonado.synthetic.SyntheticStorableReferenceAccess;
  * @author Brian S O'Neill

  */

 class IndexedCursor<S extends Storable> extends AbstractCursor<S> {

+    private static final int FETCH_AHEAD;

+

+    static {

+        String prefix = IndexedCursor.class.getName() + '.';

+        FETCH_AHEAD = Integer.getInteger(prefix + "fetchAhead", 0);

+    }

+

     private final Cursor<? extends Storable> mCursor;

     private final IndexedStorage<S> mStorage;

     private final SyntheticStorableReferenceAccess<S> mAccessor;

@@ -52,7 +60,11 @@ class IndexedCursor<S extends Storable> extends AbstractCursor<S> {
 

     IndexedCursor(Cursor<? extends Storable> indexEntryCursor,

                   IndexedStorage<S> storage,

-                  SyntheticStorableReferenceAccess<S> indexAccessor) {

+                  SyntheticStorableReferenceAccess<S> indexAccessor)

+    {

+        if (FETCH_AHEAD > 0) {

+            indexEntryCursor = new FetchAheadCursor(indexEntryCursor, FETCH_AHEAD);

+        }

         mCursor = indexEntryCursor;

         mStorage = storage;

         mAccessor = indexAccessor;