ArvinDevel commented on a change in pull request #832: Issue 620: Close the 
fileChannels for read when they are idle
URL: https://github.com/apache/bookkeeper/pull/832#discussion_r172843523
 
 

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 File path: 
bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/FileChannelBackingCache.java
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 @@ -0,0 +1,190 @@
+/*
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.bookkeeper.bookie;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import com.google.common.annotations.VisibleForTesting;
+import java.io.File;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.channels.FileChannel;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import org.apache.bookkeeper.util.IOUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * FileChannelBackingCache used to cache RefCntFileChannels for read.
+ * In order to avoid get released file, adopt design of FileInfoBackingCache.
+ * @see FileInfoBackingCache
+ */
+class FileChannelBackingCache {
+    private static final Logger LOG = 
LoggerFactory.getLogger(FileChannelBackingCache.class);
+    static final int DEAD_REF = -0xdead;
+    final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
+
+    final FileLoader fileLoader;
+
+    FileChannelBackingCache(FileLoader fileLoader) {
+        this.fileLoader = fileLoader;
+    }
+
+    final ConcurrentHashMap<Long, CachedFileChannel> fileChannels = new 
ConcurrentHashMap<>();
+
+    CachedFileChannel loadFileChannel(long logId) throws IOException {
+        lock.readLock().lock();
+        try {
+            CachedFileChannel cachedFileChannel = fileChannels.get(logId);
+            if (cachedFileChannel != null) {
+                boolean retained = cachedFileChannel.tryRetain();
+                checkArgument(retained);
+                return cachedFileChannel;
+            }
+        } finally {
+            lock.readLock().unlock();
+        }
+
+        lock.writeLock().lock();
+        try {
+            File file = fileLoader.load(logId);
+            // get channel is used to open an existing entry log file
+            // it would be better to open using read mode
+            FileChannel newFc = new RandomAccessFile(file, "r").getChannel();
+            CachedFileChannel cachedFileChannel = new CachedFileChannel(logId, 
newFc);
+            fileChannels.put(logId, cachedFileChannel);
+            boolean retained = cachedFileChannel.tryRetain();
+            checkArgument(retained);
+            return cachedFileChannel;
+        } finally {
+            lock.writeLock().unlock();
+        }
+    }
+
+    /**
+     * close FileChannel and remove from cache when possible.
+     * @param logId
+     * @param cachedFileChannel
+     */
+    private void releaseFileChannel(long logId, CachedFileChannel 
cachedFileChannel) {
+        lock.writeLock().lock();
 
 Review comment:
   Then we need some do while check in loadFileChannel. 
   I update again.

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