Fix TSAN issues in thread support library

--------------------------------------------------------

The issue was the test is attempting to check for change in variable through a while loop, but did not protect the data read using mutext lock. This could potentially lead to reading of unexpected data and cause a tsan error.

The fix wraps the checks for variable state inside the mutex lock.

lib/acl_threadsupport/test/acl_test.h

@@ -14,3 +14,4 @@ SimpleString StringFrom(uint32_t x);
 SimpleString StringFrom(uint64_t x);
 SimpleString StringFrom(intptr_t x);
 SimpleString StringFrom(size_t x);
+bool check_threadtest_state(int state, bool check_eq);

lib/acl_threadsupport/test/acl_threadsupport_test.cpp

@@ -95,7 +95,7 @@ volatile int threadvar = 0;
 
 void *test_thread(void *) {
   while (1) {
-    while (threadtest_state == SERVER_STATE)
+    while (check_threadtest_state(SERVER_STATE, true))
       acl_thread_yield();
     if (threadtest_state == END_STATE) {
       return 0;
@@ -108,6 +108,18 @@ void *test_thread(void *) {
   }
 }
 
+bool check_threadtest_state(int state, bool check_eq) {
+  bool result;
+  acl_mutex_lock(&mymutex);
+  if (check_eq) {
+    result = threadtest_state == state;
+  } else {
+    result = threadtest_state != state;
+  }
+  acl_mutex_unlock(&mymutex);
+  return result;
+}
+
 TEST(threadsupport, threads) {
   // Setup
   int res = 0;
@@ -125,15 +137,15 @@ TEST(threadsupport, threads) {
   res = acl_mutex_unlock(&mymutex);
   CHECK_EQUAL(0, res);
 
-  while (threadtest_state != SERVER_STATE)
+  while (check_threadtest_state(SERVER_STATE, false))
     acl_thread_yield();
   res = acl_mutex_lock(&mymutex);
   CHECK_EQUAL(0, res);
   CHECK_EQUAL(threadvar, 7 + 13);
   threadtest_state = CLIENT_STATE;
   res = acl_mutex_unlock(&mymutex);
   CHECK_EQUAL(0, res);
-  while (threadtest_state != SERVER_STATE)
+  while (check_threadtest_state(SERVER_STATE, false))
     acl_thread_yield();
   res = acl_mutex_lock(&mymutex);
   CHECK_EQUAL(0, res);