diff options
| author | Brian S. O'Neill <bronee@gmail.com> | 2012-01-26 02:53:21 +0000 |
|---|---|---|
| committer | Brian S. O'Neill <bronee@gmail.com> | 2012-01-26 02:53:21 +0000 |
| commit | bf9c0e6ce8568d0e37ea1d2947aba141ae4c7fe4 (patch) | |
| tree | 26b07a042caf2812c2e352286871d192d57ec625 /src/main/java/com/amazon/carbonado/cursor | |
| parent | e640c47ae16d9d375010a18facd8a5bf4bd5c83e (diff) | |
Added option for index access to fetch ahead to reduce likelihood of deadlocks.
Diffstat (limited to 'src/main/java/com/amazon/carbonado/cursor')
| -rw-r--r-- | src/main/java/com/amazon/carbonado/cursor/FetchAheadCursor.java | 73 |
1 files changed, 73 insertions, 0 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;
+ }
+}
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