bharathv commented on a change in pull request #1945:
URL: https://github.com/apache/hbase/pull/1945#discussion_r445723003
##########
File path:
hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKWatcher.java
##########
@@ -479,29 +502,15 @@ public ZNodePaths getZNodePaths() {
return znodePaths;
}
- /**
- * Method called from ZooKeeper for events and connection status.
- * <p>
- * Valid events are passed along to listeners. Connection status changes
- * are dealt with locally.
- */
- @Override
- public void process(WatchedEvent event) {
- LOG.debug(prefix("Received ZooKeeper Event, " +
- "type=" + event.getType() + ", " +
- "state=" + event.getState() + ", " +
- "path=" + event.getPath()));
-
+ void processEvent(WatchedEvent event) {
Review comment:
Done.
##########
File path:
hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKWatcher.java
##########
@@ -79,8 +86,22 @@
// listeners to be notified
private final List<ZKListener> listeners = new CopyOnWriteArrayList<>();
+ // Single threaded executor pool that processes event notifications from
Zookeeper. Events are
+ // processed in the order in which they arrive (pool backed by an unbounded
fifo queue). We do
+ // this to decouple the event processing from Zookeeper's ClientCnxn's
EventThread context.
+ // EventThread internally runs a single while loop to serially process all
the events. When events
+ // are processed by the listeners in the same thread, that blocks the
EventThread from processing
+ // subsequent events. Processing events in a separate thread frees up the
event thread to continue
+ // and further prevents deadlocks if the process method itself makes other
zookeeper calls.
+ // It is ok to do it in a single thread because the Zookeeper ClientCnxn
already serializes the
+ // requests using a single while loop and hence there is no performance
degradation.
+ private final ExecutorService zkEventProcessor =
+
Executors.newSingleThreadExecutor(Threads.getNamedThreadFactory("zk-event-processor"));
Review comment:
The reason is ThreadFactoryBuilder is from a third party library
(guava). Usually I prefer to reuse the code we already have rather than pulling
it from elsewhere. Also, making that util public doesn't matter much I guess,
its a static utility anyway.
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