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Eliminate benign race condition in DirectStreamObserver and make first and subsequent iterations consistent #33419

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Eliminate benign race condition in DirectStreamObserver and make first and subsequent iterations consistent #33419

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4 changes: 2 additions & 2 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/fn/stream/DirectStreamObserver.java
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,7 @@ public final class DirectStreamObserver<T> implements StreamObserver<T> {
private final int maxMessagesBeforeCheck;

private final Object lock = new Object();
private int numMessages = -1;
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private int numMessages;

public DirectStreamObserver(Phaser phaser, CallStreamObserver<T> outboundObserver) {
this(phaser, outboundObserver, DEFAULT_MAX_MESSAGES_BEFORE_CHECK);
Expand All @@ -69,7 +69,7 @@ public DirectStreamObserver(Phaser phaser, CallStreamObserver<T> outboundObserve
@Override
public void onNext(T value) {
synchronized (lock) {
if (++numMessages >= maxMessagesBeforeCheck) {
if (++numMessages > maxMessagesBeforeCheck) {
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it seems that with the -1 -> 0 and the >= we still have the same behavior for the first triggered check. But subsequent triggered checks would take 1 more than previous incorrect behavior.

For example if maxMessagesPerCheck was 1, before we would check on
2nd message
and then every message afterwards. But now we would correctly check every other message. So if the test fails it seems like the test was verifying the bad behavior.

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friendly ping

numMessages = 0;
int waitSeconds = 1;
int totalSecondsWaited = 0;
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