Remove recursion from TimedMutex to avoid fiber stack overflows

Summary: Under heavy contention, lock will recurse several times. This can lead to fiber stack overflow.

Differential Revision: D14936384

fbshipit-source-id: e934569a9f742859655ba3ea888ebabd4d959651

folly/fibers/TimedMutex-inl.h

@@ -79,16 +79,15 @@ TimedMutex::LockResult TimedMutex::lockHelper(WaitFunc&& waitFunc) {
 }
 
 inline void TimedMutex::lock() {
-  auto result = lockHelper([](MutexWaiter& waiter) {
+  LockResult result;
+  do {
+    result = lockHelper([](MutexWaiter& waiter) {
       waiter.baton.wait();
       return true;
     });
 
     DCHECK(result != LockResult::TIMEOUT);
-  if (result == LockResult::SUCCESS) {
-    return;
-  }
-  lock();
+  } while (result != LockResult::SUCCESS);
 }
 
 template <typename Rep, typename Period>