HBASE-22634 Improve performance of BufferedMutator

Fix findBugs

Author: sbarnoud060710

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncRequestFutureImpl.java

@@ -547,6 +547,8 @@ private RegionLocations findAllLocationsOrFail(Action action, boolean useCache)
    * @param actionsForReplicaThread original actions for replica thread; null on non-first call.
    */
     // Must be synchronized because of the background thread writeBufferPeriodicFlushTimer
+   @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="SWL_SLEEP_WITH_LOCK_HELD",
+      justification="Slots are freed while in the executor thread, so the thread is not yet available for the pool. In that case, we have a RejectedExecutionException. Sleep let some time to threads to be available again")
     synchronized void sendMultiAction(Map<ServerName, MultiAction> actionsByServer,
                                int numAttempt, List<Action> actionsForReplicaThread, boolean reuseThread) {
     // Run the last item on the same thread if we are already on a send thread.

hbase-client/src/main/java/org/apache/hadoop/hbase/client/BufferedMutatorImpl.java

@@ -301,14 +301,16 @@ public int getOperationTimeout() {
   public void flush() throws InterruptedIOException, RetriesExhaustedWithDetailsException {
     // This will avoid concurrency between period flush, flush() and close()
     // mutate are not synchronized, because it use doFlush(false)
+    boolean haveLocked = false;
     if (writeBufferPeriodicFlushTimer != null) {
       lock.lock();
+      haveLocked = false; // make sure to unlock even if writeBufferPeriodicFlushTimer is set to null before the end
     }
     try {
       checkClose();
       doFlush(true);
     } finally {
-      if (writeBufferPeriodicFlushTimer != null) {
+      if (haveLocked) {
         lock.unlock();
       }
     }
@@ -320,6 +322,8 @@ public void flush() throws InterruptedIOException, RetriesExhaustedWithDetailsEx
    * @param flushAll - if true, sends all the writes and wait for all of them to finish before
    *                 returning. Otherwise, flush until buffer size is smaller than threshold
    */
+  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="SWL_SLEEP_WITH_LOCK_HELD",
+      justification="Backpressure, when we have to many pending Future, we wait under the lock to slow down the application")
   private void doFlush(boolean flushAll) throws InterruptedIOException,
       RetriesExhaustedWithDetailsException {
     List<RetriesExhaustedWithDetailsException> errors = new ArrayList<>();

hbase-client/src/main/java/org/apache/hadoop/hbase/client/BufferedMutatorThreadPoolExecutor.java

@@ -37,6 +37,8 @@
  *          - the amount of time spent in those background threads
  */
 
+@edu.umd.cs.findbugs.annotations.SuppressWarnings(value="DLS_DEAD_LOCAL_STORE",
+    justification="Class provided as illustration for application as an alternative to the default pool")
 @InterfaceAudience.Public
 @InterfaceStability.Evolving
 public class BufferedMutatorThreadPoolExecutor extends ThreadPoolExecutor {