[GitHub] [ozone] sumitagrawl commented on a diff in pull request #3782: HDDS-7214. Continuous start & stop can have hanging threads in stopping

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

sumitagrawl commented on code in PR #3782:
URL: https://github.com/apache/ozone/pull/3782#discussion_r988739541


##########
hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/balancer/ContainerBalancer.java:
##########
@@ -893,32 +80,36 @@ private void resetState() {
   @Override
   public void notifyStatusChanged() {
     boolean shouldStop = false;
-    boolean shouldRun = false;
     lock.lock();
     try {
       if (!scmContext.isLeader() || scmContext.isInSafeMode()) {
-        shouldStop = isBalancerRunning();
-      } else {
-        shouldRun = shouldRun();
+        shouldStop = canBalancerStop();
       }
     } finally {
       lock.unlock();
     }
-
     if (shouldStop) {
       LOG.info("Stopping ContainerBalancer in this scm on status change");
       stop();
+      return;
     }
 
-    if (shouldRun) {
-      LOG.info("Starting ContainerBalancer in this scm on status change");
-      try {
-        start();
-      } catch (IllegalContainerBalancerStateException |
-          InvalidContainerBalancerConfigurationException e) {
-        LOG.warn("Could not start ContainerBalancer on raft/safe-mode " +
-            "status change.", e);
+    lock.lock();

Review Comment:
   > It is a bit inconsistent that we need to take lock for start but not for stop call above.
   
   This is done as stop has a blocking call with join, waiting thread to stop, this may take longer time. Stop lock is done inside at granular level, avoiding area of join.
   



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