user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/users/OverRide/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/OverRide">@OverRide public void onSubscribe(final Subscription s) { if (duplicateOnSubscribe) { throw new IllegalStateException("Duplicate onSubscribe() calls."); } duplicateOnSubscribe = true; } @OverRide public void onNext(final String s) { } @OverRide public void onError(final Throwable t) { } @OverRide public void onComplete() { } } If an UnsafeSubscriber instance is created in a different thread than the one that invokes onSubscribe() (true for an asynchronous Publisher), according to the java memory model, this statement inside onSubscribe(): if (duplicateOnSubscribe) { is guaranteed to compute to false if and only if the instance is published safely between these threads. None of the rules in the specifications establish a happens-before relationship between Publisher#subscribe() and Subscriber#onSubscribe(). So, the usage above can be categorized as unsafe. In a more convoluted form, the assignment: private boolean duplicateOnSubscribe = false; can be interleaved with duplicateOnSubscribe = true; such that duplicateOnSubscribe is set to false later. Has this been considered before or am I missing something? Fixes reactive-streams#486

Commits

Commits on May 7, 2020

Clarify intent of rule 1.9