[GitHub] [hbase] gkanade commented on a change in pull request #3495: HBASE-24984 WAL corruption due to early DBBs re-use when Durability.A…

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gkanade commented on a change in pull request #3495:
URL: https://github.com/apache/hbase/pull/3495#discussion_r672429950



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File path: hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/ServerCall.java
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@@ -97,11 +97,13 @@
   private long exceptionSize = 0;
   private final boolean retryImmediatelySupported;
 
-  // This is a dirty hack to address HBASE-22539. The lowest bit is for normal rpc cleanup, and the
-  // second bit is for WAL reference. We can only call release if both of them are zero. The reason
-  // why we can not use a general reference counting is that, we may call cleanup multiple times in
-  // the current implementation. We should fix this in the future.
-  private final AtomicInteger reference = new AtomicInteger(0b01);
+  // This is a dirty hack to address HBASE-22539. The highest bit is for rpc ref and cleanup, and
+  // the rest of the bits are for WAL reference count. We can only call release if all of them are
+  // zero. The reason why we can not use a general reference counting is that, we may call cleanup
+  // multiple times in the current implementation. We should fix this in the future.
+  // The refCount here will start as 0x80000000 and increment with every WAL reference and decrement
+  // from WAL side on release
+  private final AtomicInteger reference = new AtomicInteger(0x80000000);

Review comment:
       Right - as @Apache9 mentions above, the check whether rpc ref is false AND wal reference count = 0 needs to happen atomically and make sure the ByteBuffer is released exactly once. Thus single atomicinteger mechanism provides synchronized way of dealing with this @anoopsjohn FYI




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