Prevent concurrent cancellations of data plane call in ExternalProcessorClientInterceptor - #12996
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…sorClientInterceptor If the ext-proc stream terminates with a non-OK status, the interceptor cancels the downstream data plane call (on the executor thread). Concurrently, the application thread may call cancel() on the returned proxy call (e.g. for user cancellation or cleanup). Since ClientCallImpl does not synchronize its cancelCalled field, concurrent cancellations from these two threads resulted in a TSAN data race (that was discussed in grpc#12975). This commit introduces an AtomicBoolean downstreamCancelled in DataPlaneClientCall to guard all downstream cancellations, ensuring that only the first cancellation is forwarded to delayedCall/super.cancel(). This deduplicates and serializes cancellation handling from both the application and the interceptor threads, preventing the data race.
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If the ext-proc stream terminates with a non-OK status, the interceptor cancels the downstream data plane call (on the executor thread). Concurrently, the application thread may call cancel() on the returned proxy call (e.g. for user cancellation or cleanup).
Since ClientCallImpl does not synchronize its cancelCalled field, concurrent cancellations from these two threads resulted in a TSAN data race (that was discussed in #12975).
This commit introduces an AtomicBoolean downstreamCancelled in DataPlaneClientCall to guard all downstream cancellations, ensuring that only the first cancellation is forwarded to delayedCall/super.cancel(). This deduplicates and serializes cancellation handling from both the application and the interceptor threads, preventing the data race.