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https://issues.apache.org/jira/browse/BEAM-5211?focusedWorklogId=137646&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-137646
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ASF GitHub Bot logged work on BEAM-5211:
----------------------------------------
Author: ASF GitHub Bot
Created on: 24/Aug/18 02:54
Start Date: 24/Aug/18 02:54
Worklog Time Spent: 10m
Work Description: tweise commented on a change in pull request #6271:
[BEAM-5211] Flink Streaming ExecutableStage operator chain blocks grpc receiver
threads
URL: https://github.com/apache/beam/pull/6271#discussion_r212509932
##########
File path:
runners/flink/src/main/java/org/apache/beam/runners/flink/translation/wrappers/streaming/ExecutableStageDoFnOperator.java
##########
@@ -137,12 +137,32 @@ private void
processElementWithSdkHarness(WindowedValue<InputT> element) throws
checkState(
stateRequestHandler != null, "%s not yet prepared",
StateRequestHandler.class.getName());
+ final ArrayList<KV<String, OutputT>> results = new ArrayList();
+
+ OutputReceiverFactory receiverFactory =
+ new OutputReceiverFactory() {
+ @Override
+ public FnDataReceiver<OutputT> create(String pCollectionId) {
+ return (receivedElement) -> {
+ synchronized (results) {
+ // buffer to not block the grpc thread
+ results.add(KV.of(pCollectionId, receivedElement));
+ }
+ };
+ }
+ };
+
try (RemoteBundle bundle =
- stageBundleFactory.getBundle(
- new ReceiverFactory(outputManager, outputMap),
stateRequestHandler, progressHandler)) {
+ stageBundleFactory.getBundle(receiverFactory, stateRequestHandler,
progressHandler)) {
logger.debug(String.format("Sending value: %s", element));
// TODO(BEAM-4681): Add support to Flink to support portable timers.
Iterables.getOnlyElement(bundle.getInputReceivers().values()).accept(element);
+ // TODO: it would be nice to emit results as they arrive, can thread
wait non-blocking?
+ }
+
+ // RemoteBundle close blocks until all results are received
+ for (KV<String, OutputT> result : results) {
Review comment:
Flink operators (and probably their entire chain) cannot be assumed to be
thread-safe. The best solution would be to use the thread that is blocking for
the end of the bundle. The next best thing would be a single output background
thread and synchronize after the bundle is closed. At this time that isn't the
top priority though..
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Issue Time Tracking
-------------------
Worklog Id: (was: 137646)
Time Spent: 1h (was: 50m)
> Flink Streaming ExecutableStage operator chain blocks grpc receiver threads
> ----------------------------------------------------------------------------
>
> Key: BEAM-5211
> URL: https://issues.apache.org/jira/browse/BEAM-5211
> Project: Beam
> Issue Type: Bug
> Components: runner-flink
> Affects Versions: 2.6.0
> Reporter: Thomas Weise
> Assignee: Thomas Weise
> Priority: Major
> Labels: portability
> Fix For: 2.7.0
>
> Attachments: jstack.log
>
> Time Spent: 1h
> Remaining Estimate: 0h
>
> The operator attempts to emit results as they are received, within the grpc
> thread, while the subtask thread is waiting for bundle completion. This leads
> to blocking of grpc threads and eventually deadlock when multiple stages are
> within an operator chain. Observed with wordcount, see attached stacktrace.
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