semaphore.h: handle spurious wakeups in TimedWait() on Linux#1021
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
github-actionsbot added the tests: in-progress 
dconeybe removed the tests: in-progress github-actionsbot added the tests: in-progress 
❌ Integration test FAILEDRequested by @dconeybe on commit 26e918b
Add flaky tests to go/fpl-cpp-flake-tracker |
github-actionsbot added the tests: succeeded 
firebase-workflow-triggerbot removed the tests: in-progress dconeybe added the tests-requested: quick github-actionsbot added tests: in-progress firebase-workflow-triggerbot removed the tests: in-progress dconeybe added tests-requested: quick github-actionsbot added tests: in-progress 
DellaBitta requested changes Jul 11, 2022
DellaBitta approved these changes Jul 11, 2022
firebase-workflow-triggerbot removed the tests: in-progress github-actionsbot added the tests: succeeded github-actionsbot added tests: in-progress 
| // Return failure, since the timeout expired. | ||
| return false; | ||
| case EINVAL: | ||
| assert("sem_timedwait() failed with EINVAL" == 0); |
There was a problem hiding this comment.
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) { | |||
There was a problem hiding this comment.
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?)
firebase-workflow-triggerbot removed the tests: in-progress 
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:
|
dconeybe added a commit that referenced this pull request Jul 20, 2022
…s with the TimedWait() fix in #1021
Sign up for freeto subscribe to this conversation on GitHub. Already have an account? Sign in.
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
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).