semaphore.h: handle spurious wakeups in TimedWait() on Linux #1021
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❌ Integration test FAILEDRequested by @dconeybe on commit 26e918b
Add flaky tests to go/fpl-cpp-flake-tracker |
DellaBitta
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Jul 9, 2022
DellaBitta
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Jul 9, 2022
DellaBitta
requested changes
Jul 11, 2022
DellaBitta
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Jul 11, 2022
jonsimantov
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Jul 11, 2022
| // Return failure, since the timeout expired. | ||
| return false; | ||
| case EINVAL: | ||
| assert("sem_timedwait() failed with EINVAL" == 0); |
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Just making sure, you want this to NOT actually assert in release builds, yes? (the default assert behavior?)
| @@ -172,7 +172,30 @@ class Semaphore { | |||
| return WaitForSingleObject(semaphore_, milliseconds) == 0; | |||
| #else // not windows and not mac - should be Linux. | |||
| timespec t = internal::MsToAbsoluteTimespec(milliseconds); | |||
| return sem_timedwait(semaphore_, &t) == 0; | |||
| while (true) { | |||
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Would it be possible to add a test exercising this failure/fix to semaphore_test.cc? (Or, even better, does re-enabling the disabled MultithreadedStressTest in that file now work?)
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Vindication! One of the nightly test runs failed with this assertion failure: semaphore.h:189: bool firebase::Semaphore::TimedWait(int): Assertion `"sem_timedwait() failed with EINVAL" == 0' failed. https://github.com/firebase/firebase-cpp-sdk/runs/7338303645 According to https://linux.die.net/man/3/sem_timedwait, EINVAL occurs in one of two cases:
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dconeybe
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…s with the TimedWait() fix in #1021
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This fixes a latent bug where
Future::Wait(int timeout_milliseconds)would occasionally return prematurely, when neither the timeout had expired nor the Future been completed. This was due to the implementation ofSemaphore::TimedWait(int milliseconds)which callssem_timedwait()on Linux and Android and neglected to check if theerrnowasEINTR, in which case the wait should be restarted.This bug surfaced as the integration tests for Firestore's
TransactionTest.TestMaxAttemptsflakily failing due to a call toFuture.Await(int timeout_milliseconds)returning as if it had timed out when, in fact, no timeout had occurred.Note that this fix only affects Linux and Android (which runs Linux under the hood).