[GitHub] [ozone] lokeshj1703 commented on a diff in pull request #3535: HDDS-6928. ozone container balancer CLI went in hung state due to deadlock

[GitBox <gi...@apache.org>]

lokeshj1703 commented on code in PR #3535:
URL: https://github.com/apache/ozone/pull/3535#discussion_r908222198


##########
hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/balancer/ContainerBalancer.java:
##########
@@ -1032,16 +1048,30 @@ private void validateState(boolean expectedRunning)
    */
   @Override
   public void stop() {
+    Thread balancingThread;
     lock.lock();
     try {
       if (!isBalancerRunning()) {
         LOG.warn("Cannot stop Container Balancer because it's not running");
         return;
       }
-      stopBalancingThread();
+      balancingThread = currentBalancingThread;
+      currentBalancingThread = null;
     } finally {
       lock.unlock();
     }
+
+    // wait for balancingThread to die
+    if (balancingThread != null &&

Review Comment:
   Can we add a preconditions check here that lock is not held by the current thread? There is an api for it.



##########
hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/balancer/ContainerBalancer.java:
##########
@@ -839,20 +850,34 @@ private void resetState() {
   @Override
   public void notifyStatusChanged() {
     if (!scmContext.isLeader() || scmContext.isInSafeMode()) {
-      if (isBalancerRunning()) {
+      boolean shouldStop = false;
+
+      // lock here to ensure no change is made to the balancing thread while
+      // we're reading it
+      lock.lock();
+      try {
+        shouldStop = isBalancerRunning();

Review Comment:
   I would suggest merging the two lock sections and afterwards stop can be called.



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