Fix issue 906

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index 2ef04569b9fc6889f030f795ff2ee916a604b5ef..77d09a05550343a9cf80dfbf254a43e77c4e6e89 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/runtime/vm/dart_api_impl_test.cc
@@ -2912,7 +2912,11 @@ void BusyLoop_start(uword unused) {
 // on the third interrupt.
 static int interrupt_count = 0;
 static bool IsolateInterruptTestCallback() {
-  interrupt_count++;
+  {
+    MonitorLocker ml(sync);
+    interrupt_count++;
+    ml.Notify();
+  }
   OS::Print(" =========== Interrupt callback called #%d\n", interrupt_count);
   if (interrupt_count >= 3) {
     Dart_EnterScope();
@@ -2948,11 +2952,17 @@ TEST_CASE(IsolateInterrupt) {
   // Send three interrupts to the other isolate.  The first two allow
   // execution to continue.  The third causes an exception in the
   // isolate.
-  Dart_InterruptIsolate(shared_isolate);
-  OS::Sleep(5);
-  Dart_InterruptIsolate(shared_isolate);
-  OS::Sleep(5);
-  Dart_InterruptIsolate(shared_isolate);
+  for (int i = 0; i < 3; i++) {
+    Dart_InterruptIsolate(shared_isolate);
+    OS::Sleep(5);
+    {
+      MonitorLocker ml(sync);
+      // Wait for interrupt_count to be increased.
+      while (interrupt_count == i) {
+        ml.Wait();
+      }
+    }
+  }
 
   {
     MonitorLocker ml(sync);