semaphore.h: handle spurious wakeups in TimedWait() on Linux (#1021)

Author: dconeybe

app/src/semaphore.h

@@ -172,7 +172,30 @@ class Semaphore {
 returnWaitForSingleObject(semaphore_, milliseconds) == 0;
 #else// not windows and not mac - should be Linux.
 timespec t = internal::MsToAbsoluteTimespec(milliseconds);
-returnsem_timedwait(semaphore_, &t) == 0;
+while (true) {
+int result = sem_timedwait(semaphore_, &t);
+if (result == 0) {
+// Return success, since we successfully locked the semaphore.
+returntrue;
+ }
+switch (errno) {
+case EINTR:
+// Restart the wait because we were woken up spuriously.
+continue;
+case ETIMEDOUT:
+// Return failure, since the timeout expired.
+returnfalse;
+case EINVAL:
+assert("sem_timedwait() failed with EINVAL" == 0);
+returnfalse;
+case EDEADLK:
+assert("sem_timedwait() failed with EDEADLK" == 0);
+returnfalse;
+default:
+assert("sem_timedwait() failed with an unknown error" == 0);
+returnfalse;
+ }
+ }
 #endif
  }
 

release_build_files/readme.md

@@ -634,6 +634,13 @@ workflow use only during the development of your app, not for publicly shipping
 code.
 
 ## Release Notes
+### Upcoming Changes
+- Changes
+- General (Android,Linux): Fixed a concurrency bug where waiting for an
+ event with a timeout could occasionally return prematurely, as if the
+ timeout had occurred
+ ([#1021](https://github.com/firebase/firebase-cpp-sdk/pull/1021)).
+
 ### 9.2.0
 - Changes
 - GMA: Added the Google Mobile Ads SDK with updated support for AdMob. See