[GitHub] [hbase] bharathv commented on a change in pull request #934: HBASE-23568: Improve Threading of Replication

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

bharathv commented on a change in pull request #934: HBASE-23568: Improve Threading of Replication
URL: https://github.com/apache/hbase/pull/934#discussion_r373907685
 
 

 ##########
 File path: hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/ReplicationSource.java
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 @@ -304,31 +318,56 @@ private void initializeWALEntryFilter(UUID peerClusterId) {
     this.walEntryFilter = new ChainWALEntryFilter(filters);
   }
 
-  private void tryStartNewShipper(String walGroupId, PriorityBlockingQueue<Path> queue) {
-    workerThreads.compute(walGroupId, (key, value) -> {
-      if (value != null) {
-        if (LOG.isDebugEnabled()) {
-          LOG.debug(
-              "{} Someone has beat us to start a worker thread for wal group {}",
-              logPeerId(), key);
-        }
-        return value;
-      } else {
-        if (LOG.isDebugEnabled()) {
-          LOG.debug("{} Starting up worker for wal group {}", logPeerId(), key);
+  /**
+   * Synchronized method so that only one item is inserted at a time. Should be the only place that
+   * insertions are performed on the workerThreads data structure.
+   *
+   * @param walGroupId The WAL group ID
+   * @param queue The queue of paths to process
+   */
+  private synchronized void tryStartNewShipper(final String walGroupId,
+      final PriorityBlockingQueue<Path> queue) {
+
+    if (workerThreads.containsKey(walGroupId)) {
+      return;
+    }
+
+    LOG.debug("{} Register worker for wallGroupID {}", logPeerId(), walGroupId);
 
 Review comment:
   nit: I think you need a isDebugEnabled() check because logPeerId() has an unnecessary string construction when debug log is not enabled.

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