Fix potential race condition on CTS TC pthread_gettid_np

Root cause:
If start_routine thread exits before pthread_gettid_np is invokded, the "tid" field
will be cleared so that pthread_gettid_np will get "0" (which is cleared by kernel, 
due to the flag "CLONE_CHILD_CLEARTID" is set while calling clone system call inside

Proposed patch:
Use a mutex to guarantee pthread_gettid_np will be invoked and returned before the
start_routine exits

Signed-off-by: Junjie Hu <>

Change-Id: I22411f1b0f7446d76a0373cef4ccec858fac7018
diff --git a/tests/pthread_test.cpp b/tests/pthread_test.cpp
old mode 100644
new mode 100755
index 8ae28d8..f15cdab
--- a/tests/pthread_test.cpp
+++ b/tests/pthread_test.cpp
@@ -1244,8 +1244,11 @@
 #if defined(__BIONIC__)
+static pthread_mutex_t gettid_mutex;
 static void* pthread_gettid_np_helper(void* arg) {
+  pthread_mutex_lock(&gettid_mutex);
   *reinterpret_cast<pid_t*>(arg) = gettid();
+  pthread_mutex_unlock(&gettid_mutex);
   return NULL;
@@ -1256,11 +1259,15 @@
   pid_t t_gettid_result;
   pthread_t t;
+  pthread_mutex_init(&gettid_mutex, NULL);
+  pthread_mutex_lock(&gettid_mutex);
   pthread_create(&t, NULL, pthread_gettid_np_helper, &t_gettid_result);
   pid_t t_pthread_gettid_np_result = pthread_gettid_np(t);
+  pthread_mutex_unlock(&gettid_mutex);
   pthread_join(t, NULL);
+  pthread_mutex_destroy(&gettid_mutex);
   ASSERT_EQ(t_gettid_result, t_pthread_gettid_np_result);