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Fix race condition in SpliceFlatStreamToMetaSingle #1845

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Sep 29, 2021
Merged

Fix race condition in SpliceFlatStreamToMetaSingle #1845

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13 changes: 9 additions & 4 deletions ...talk-http-netty/src/main/java/io/servicetalk/http/netty/SpliceFlatStreamToMetaSingle.java
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
import io.servicetalk.concurrent.api.PublisherToSingleOperator;
import io.servicetalk.concurrent.api.Single;
import io.servicetalk.concurrent.api.internal.SubscribablePublisher;
import io.servicetalk.concurrent.internal.DelayedSubscription;
import io.servicetalk.concurrent.internal.DuplicateSubscribeException;
import io.servicetalk.http.api.HttpResponseMetaData;
import io.servicetalk.http.api.StreamingHttpResponse;
Expand Down Expand Up @@ -74,7 +75,7 @@ public PublisherSource.Subscriber<Object> apply(Subscriber<? super Data> subscri

/* Visible for testing */
static final class SplicingSubscriber<Data, MetaData, Payload> implements PublisherSource.Subscriber<Object> {

@SuppressWarnings("rawtypes")
private static final AtomicReferenceFieldUpdater<SplicingSubscriber, Object>
maybePayloadSubUpdater = AtomicReferenceFieldUpdater.newUpdater(SplicingSubscriber.class,
Object.class, "maybePayloadSub");
Expand Down Expand Up @@ -225,17 +226,21 @@ private Publisher<Payload> newPayloadPublisher() {
return new SubscribablePublisher<Payload>() {
@Override
protected void handleSubscribe(PublisherSource.Subscriber<? super Payload> newSubscriber) {
final DelayedSubscription delayedSubscription = new DelayedSubscription();
// newSubscriber.onSubscribe MUST be called before making newSubscriber visible below with the CAS
// on maybePayloadSubUpdater. Otherwise there is a potential for concurrent invocation on the
// Subscriber which is not allowed by the Reactive Streams specification.
newSubscriber.onSubscribe(delayedSubscription);
if (maybePayloadSubUpdater.compareAndSet(SplicingSubscriber.this, PENDING, newSubscriber)) {
// TODO risk of a race here with terminal events, will be addressed in follow-up PR
assert rawSubscription != null;
newSubscriber.onSubscribe(rawSubscription);
delayedSubscription.delayedSubscription(rawSubscription);
} else {
// Entering this branch means either a duplicate subscriber or a stream that completed or failed
// without a subscriber present. The consequence is that unless we've seen payload data we may
// not send onComplete() or onError() to the original subscriber, but that is OK as long as one
// subscriber of them gets the correct signal and all others get a duplicate subscriber error.
final Object maybeSubscriber = SplicingSubscriber.this.maybePayloadSub;
newSubscriber.onSubscribe(EMPTY_SUBSCRIPTION);
delayedSubscription.delayedSubscription(EMPTY_SUBSCRIPTION);
if (maybeSubscriber == EMPTY_COMPLETED && maybePayloadSubUpdater
.compareAndSet(SplicingSubscriber.this, EMPTY_COMPLETED, EMPTY_COMPLETED_DELIVERED)) {
// Prematurely completed (header + empty payload)
Expand Down