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

firebase · Jul 11, 2022 · 26e918b · 26e918b
1 parent c722ca7
commit 26e918b
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Showing 2 changed files with 31 additions and 1 deletion.
diff --git a/app/src/semaphore.h b/app/src/semaphore.h
@@ -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) {
+      int result = sem_timedwait(semaphore_, &t);
+      if (result == 0) {
+        // Return success, since we successfully locked the semaphore.
+        return true;
+      }
+      switch (errno) {
+        case EINTR:
+          // Restart the wait because we were woken up spuriously.
+          continue;
+        case ETIMEDOUT:
+          // Return failure, since the timeout expired.
+          return false;
+        case EINVAL:
+          assert("sem_timedwait() failed with EINVAL" == 0);
+          return false;
+        case EDEADLK:
+          assert("sem_timedwait() failed with EDEADLK" == 0);
+          return false;
+        default:
+          assert("sem_timedwait() failed with an unknown error" == 0);
+          return false;
+      }
+    }
 #endif
   }
 

diff --git a/release_build_files/readme.md b/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