From bf9c0e6ce8568d0e37ea1d2947aba141ae4c7fe4 Mon Sep 17 00:00:00 2001
From: "Brian S. O'Neill" <bronee@gmail.com>
Date: Thu, 26 Jan 2012 02:53:21 +0000
Subject: Added option for index access to fetch ahead to reduce likelihood of
 deadlocks.

---
 .../amazon/carbonado/cursor/FetchAheadCursor.java  | 73 ++++++++++++++++++++++
 .../carbonado/repo/indexed/IndexedCursor.java      | 14 ++++-
 2 files changed, 86 insertions(+), 1 deletion(-)
 create mode 100644 src/main/java/com/amazon/carbonado/cursor/FetchAheadCursor.java

(limited to 'src/main/java/com/amazon/carbonado')

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;
-- 
cgit v1.2.3