ivankelly 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_r167181725
 
 

 ##########
 File path: 
bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/EntryLogger.java
 ##########
 @@ -1094,24 +1259,25 @@ private Header getHeaderForLogId(long entryLogId) 
throws IOException {
     }
 
     private BufferedReadChannel getChannelForLogId(long entryLogId) throws 
IOException {
-        BufferedReadChannel fc = getFromChannels(entryLogId);
-        if (fc != null) {
-            return fc;
-        }
-        File file = findFile(entryLogId);
-        // 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();
-        FileChannel oldFc = logid2FileChannel.putIfAbsent(entryLogId, newFc);
-        if (null != oldFc) {
-            newFc.close();
-            newFc = oldFc;
+        BufferedReadChannel brc = getFromChannels(entryLogId);
+        if (brc != null) {
+            return brc;
+        }
+        FileChannelBackingCache.CachedFileChannel cachedFileChannel = null;
+        try {
+            do {
+                cachedFileChannel = 
logid2FileChannel.loadFileChannel(entryLogId);
+            } while (!cachedFileChannel.tryRetain());
+        } finally {
+            if (null != cachedFileChannel) {
+                cachedFileChannel.release();
 
 Review comment:
   the refcount for loadFileChannel belongs to the cache.
   the refcount for tryRetain belongs to the created BufferedReadChannel.
   
   If the CachedFileChannel is invalidated from the cache, you don't want it to 
be closed immediately, you want it to be closed when the BufferedReadChannel 
releases it. Similarly, if the BufferedReadChannel releases it, and it is still 
in the cache, you don't want to close the file channel, as the cache may hand 
it out to another caller. So you need both of them to hold a refcount.

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