Fix for issue 26511 (VM hangs waiting for all threads that are not already at

runtime/vm/lockers.cc

Index: runtime/vm/lockers.cc
diff --git a/runtime/vm/lockers.cc b/runtime/vm/lockers.cc
index 2efe2458b927339fe57752d3eb575565b2f39198..b8ac4b64c84f27ce4180e057526fd77f9ac2d8fc 100644
--- a/runtime/vm/lockers.cc
+++ b/runtime/vm/lockers.cc
@@ -12,11 +12,11 @@ namespace dart {
 static void updateThreadState(Thread* thread) {
   // 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);
+  uint32_t 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) {
+  if (AtomicOperations::CompareAndSwapUint32(
+          reinterpret_cast<uint32_t*>(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();
@@ -34,11 +34,11 @@ Monitor::WaitResult MonitorLocker::WaitWithSafepointCheck(Thread* thread,
   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);
+  uint32_t 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) {
+  if (AtomicOperations::CompareAndSwapUint32(
+          reinterpret_cast<uint32_t*>(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();
@@ -98,11 +98,11 @@ Monitor::WaitResult SafepointMonitorLocker::Wait(int64_t millis) {
     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);
+    uint32_t 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) {
+    if (AtomicOperations::CompareAndSwapUint32(
+            reinterpret_cast<uint32_t*>(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();