Fix DemandBuffer Data Races #3514
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We're still seeing crashes due to what look like data races in `DemandBuffer`. Here, I'm making fixes based on what appears to have helped in pointfreeco#3447: In `buffer(value:)`: * Check if the demand is unlimited and, if so, unlock before calling `subscriber.receive(value)`. * If the demand is not unlimited, append the value to the buffer and call `flush()` after unlocking. In `flush(adding:)`: * Process values in a loop, acquiring and releasing the lock around shared state access. * Unlock before calling `subscriber.receive(value)` to avoid holding the lock during subscriber calls. * After sending a value, lock again to update `demandState.requested` with any additional demand returned by the subscriber. * Ensure that `subscriber.receive(completion:)` is called outside the lock. Also add a new `DemandBufferTests` test file. I added some tests that I was hoping would fail without the above changes, but they all pass both before and after, even with ThreadSanitizer enabled.
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@jpsim Maybe there are some fixes upstream that we could bring in? And/or maybe you should share these fixes back with CombineExt? /cc @freak4pc |
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We're still seeing crashes due to what look like data races in
DemandBuffer. Here, I'm making speculative fixes based on what appears to have helped in #3447:In
buffer(value:):subscriber.receive(value).flush()after unlocking.In
flush(adding:):subscriber.receive(value)to avoid holding the lock during subscriber calls.demandState.requestedwith any additional demand returned by the subscriber.subscriber.receive(completion:)is called outside the lock.Also add a new
DemandBufferTeststest file. I added some tests that I was hoping would fail without the above changes, but they all pass both before and after, even with ThreadSanitizer enabled.