Check for Thread::Current being non NULL as in some situations (shutdown) it could be NULL.

runtime/vm/lockers.cc

Index: runtime/vm/lockers.cc
diff --git a/runtime/vm/lockers.cc b/runtime/vm/lockers.cc
index 8eddc7390f3f20aa06bb4b8e78ced906ac3c4463..2efe2458b927339fe57752d3eb575565b2f39198 100644
--- a/runtime/vm/lockers.cc
+++ b/runtime/vm/lockers.cc
@@ -57,11 +57,15 @@ SafepointMutexLocker::SafepointMutexLocker(Mutex* mutex) : mutex_(mutex) {
     // 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();
-    mutex->Lock();
-    // Update thread state and block if a safepoint operation is in progress.
-    updateThreadState(thread);
+    if (thread != NULL) {
+      thread->set_execution_state(Thread::kThreadInBlockedState);
+      thread->EnterSafepoint();
+      mutex->Lock();
+      // Update thread state and block if a safepoint operation is in progress.
+      updateThreadState(thread);
+    } else {
+      mutex->Lock();
+    }
   }
 }
 
@@ -73,36 +77,44 @@ SafepointMonitorLocker::SafepointMonitorLocker(Monitor* monitor)
     // 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();
-    // Update thread state and block if a safepoint operation is in progress.
-    updateThreadState(thread);
+    if (thread != NULL) {
+      thread->set_execution_state(Thread::kThreadInBlockedState);
+      thread->EnterSafepoint();
+      monitor_->Enter();
+      // Update thread state and block if a safepoint operation is in progress.
+      updateThreadState(thread);
+    } else {
+      monitor_->Enter();
+    }
   }
 }
 
 
 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();
+  if (thread != NULL) {
+    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;
+  } else {
+    return monitor_->Wait(millis);
   }
-  thread->set_execution_state(Thread::kThreadInVM);
-  return result;
 }
 
 }  // namespace dart