Handles spurious wake-ups in pthread_join()
Removed 'join_count' from pthread_internal_t and switched to using the flag
PTHREAD_ATTR_FLAG_JOINED to indicate if a thread is being joined. Combined with
a switch to a while loop in pthread_join, this fixes spurious wake-ups but
prevents a thread from being joined multiple times. This is fine for
two reasons:
1) The pthread_join specification allows for undefined behavior when multiple
threads try to join a single thread.
2) There is no thread safe way to allow multiple threads to join a single
thread with the pthread interface. The second thread calling pthread_join
could be pre-empted until the thread is destroyed and its handle reused for
a different thread. Therefore multi-join is always an error.
Bug: https://code.google.com/p/android/issues/detail?id=52255
Change-Id: I8b6784d47620ffdcdbfb14524e7402e21d46c5f7
diff --git a/tests/pthread_test.cpp b/tests/pthread_test.cpp
index a86cadc..d754312 100644
--- a/tests/pthread_test.cpp
+++ b/tests/pthread_test.cpp
@@ -317,3 +317,25 @@
ASSERT_EQ(ESRCH, pthread_kill(dead_thread, 0));
}
+
+TEST(pthread, pthread_join__multijoin) {
+ bool done = false;
+
+ pthread_t t1;
+ ASSERT_EQ(0, pthread_create(&t1, NULL, SpinFn, &done));
+
+ pthread_t t2;
+ ASSERT_EQ(0, pthread_create(&t2, NULL, JoinFn, reinterpret_cast<void*>(t1)));
+
+ sleep(1); // (Give t2 a chance to call pthread_join.)
+
+ // Multiple joins to the same thread should fail.
+ ASSERT_EQ(EINVAL, pthread_join(t1, NULL));
+
+ done = true;
+
+ // ...but t2's join on t1 still goes ahead (which we can tell because our join on t2 finishes).
+ void* join_result;
+ ASSERT_EQ(0, pthread_join(t2, &join_result));
+ ASSERT_EQ(0, reinterpret_cast<int>(join_result));
+}