- Add assertions in MutexLocker/MonitorLocker to ensure that the code enclosed

runtime/vm/lockers.cc

Index: runtime/vm/lockers.cc
diff --git a/runtime/vm/lockers.cc b/runtime/vm/lockers.cc
index 839d40ccdb43d03bd1393e715dc725be89176923..ba70bca9bb2cd8738c14b59707495b3887c13ad2 100644
--- a/runtime/vm/lockers.cc
+++ b/runtime/vm/lockers.cc
@@ -59,4 +59,55 @@ SafepointMutexLocker::SafepointMutexLocker(Mutex* mutex) : mutex_(mutex) {
   }
 }
 
+
+SafepointMonitorLocker::SafepointMonitorLocker(Monitor* monitor)
+    : monitor_(monitor) {
+  ASSERT(monitor_ != NULL);
+  if (!monitor_->TryEnter()) {
+    // We did not get the lock and could potentially block, so transition
+    // accordingly.
+    Thread* thread = Thread::Current();
+    thread->set_execution_state(Thread::kThreadInBlockedState);
+    thread->EnterSafepoint();
+    monitor_->Enter();
+    // First try a fast update of the thread state to indicate it is not at a
+    // safepoint anymore.
+    uword old_state = Thread::SetAtSafepoint(true, 0);
+    uword addr =
+        reinterpret_cast<uword>(thread) + Thread::safepoint_state_offset();
+    if (AtomicOperations::CompareAndSwapWord(
+            reinterpret_cast<uword*>(addr), old_state, 0) != old_state) {
+      // Fast update failed which means we could potentially be in the middle
+      // of a safepoint operation and need to block for it.
+      SafepointHandler* handler = thread->isolate()->safepoint_handler();

[Cutch, 2016/03/01 15:08:07]

This 'fast update of the thread state' code is the same as SafepointMutexLocker.
Maybe factor it out into a common routine?

[siva, 2016/03/01 18:59:53]

Done.

+      handler->ExitSafepointUsingLock(thread);
+    }
+    thread->set_execution_state(Thread::kThreadInVM);
+  }
+}
+
+
+Monitor::WaitResult SafepointMonitorLocker::Wait(int64_t millis) {
+  Thread* thread = Thread::Current();
+  thread->set_execution_state(Thread::kThreadInBlockedState);
+  thread->EnterSafepoint();
+  Monitor::WaitResult result = monitor_->Wait(millis);
+  // First try a fast update of the thread state to indicate it is not at a
+  // safepoint anymore.
+  uword old_state = Thread::SetAtSafepoint(true, 0);
+  uword addr =
+      reinterpret_cast<uword>(thread) + Thread::safepoint_state_offset();
+  if (AtomicOperations::CompareAndSwapWord(
+          reinterpret_cast<uword*>(addr), old_state, 0) != old_state) {
+    // Fast update failed which means we could potentially be in the middle
+    // of a safepoint operation and need to block for it.
+    monitor_->Exit();
+    SafepointHandler* handler = thread->isolate()->safepoint_handler();
+    handler->ExitSafepointUsingLock(thread);
+    monitor_->Enter();
+  }
+  thread->set_execution_state(Thread::kThreadInVM);
+  return result;
+}
+
 }  // namespace dart