1. Get rid of SwitchIsolateScope as it is not clear when this should be used and there is also a bug in that Thread::ExitIsolate is not called if saved_isolate is not NULL

2. Added Dart::ShutDownIsolate(Isolate* isolate) to take care of ensuring that the isolate is entered before shutting it down and deal with the asymmetry on the way out.

R=zra@google.com

Review URL: https://codereview.chromium.org/1427583009 .

runtime/vm/dart.cc

@@ -395,6 +395,17 @@ void Dart::RunShutdownCallback() {
 }
 
 
+void Dart::ShutdownIsolate(Isolate* isolate) {
+  ASSERT(Isolate::Current() == NULL);
+  // We need to enter the isolate in order to shut it down.
+  Thread::EnterIsolate(isolate);
+  ShutdownIsolate();
+  // Since the isolate is shutdown and deleted, there is no need to
+  // exit the isolate here.
+  ASSERT(Isolate::Current() == NULL);
+}
+
+
 void Dart::ShutdownIsolate() {
   Isolate* isolate = Isolate::Current();
   isolate->Shutdown();

runtime/vm/dart.h

@@ -39,6 +39,7 @@ class Dart : public AllStatic {
                                 const Dart_IsolateFlags& api_flags);
   static RawError* InitializeIsolate(const uint8_t* snapshot, void* data);
   static void RunShutdownCallback();
+  static void ShutdownIsolate(Isolate* isolate);
   static void ShutdownIsolate();
 
   static Isolate* vm_isolate() { return vm_isolate_; }

runtime/vm/dart_api_impl.cc

@@ -1660,8 +1660,9 @@ DART_EXPORT Dart_Handle Dart_RunLoop() {
   Monitor monitor;
   MonitorLocker ml(&monitor);
   {
-    SwitchIsolateScope switch_scope(NULL);
-
+    // The message handler run loop does not expect to have a current isolate
+    // so we exit the isolate here and enter it again after the runloop is done.
+    Thread::ExitIsolate();
     RunLoopData data;
     data.monitor = &monitor;
     data.done = false;
@@ -1671,6 +1672,7 @@ DART_EXPORT Dart_Handle Dart_RunLoop() {
     while (!data.done) {
       ml.Wait();
     }
+    Thread::EnterIsolate(I);
   }
   if (I->object_store()->sticky_error() != Object::null()) {
     Dart_Handle error = Api::NewHandle(I, I->object_store()->sticky_error());

runtime/vm/isolate.cc

@@ -1454,11 +1454,8 @@ static void ShutdownIsolate(uword parameter) {
     }
     Dart::RunShutdownCallback();
   }
-  {
-    // Shut the isolate down.
-    SwitchIsolateScope switch_scope(isolate);
-    Dart::ShutdownIsolate();
-  }
+  // Shut the isolate down.
+  Dart::ShutdownIsolate(isolate);
 }
 
 
@@ -1664,6 +1661,9 @@ void Isolate::Shutdown() {
 
   Thread* thread = Thread::Current();
 
+  // Don't allow anymore dart code to execution on this isolate.
+  ClearStackLimit();
+
   // First, perform higher-level cleanup that may need to allocate.
   {
     // Ensure we have a zone and handle scope so that we can call VM functions.

runtime/vm/isolate.h

@@ -912,48 +912,6 @@ class StartIsolateScope {
   DISALLOW_COPY_AND_ASSIGN(StartIsolateScope);
 };
 
-// When we need to temporarily become another isolate, we use the
-// SwitchIsolateScope.  It is not permitted to run dart code while in
-// a SwitchIsolateScope.
-class SwitchIsolateScope {
- public:
-  explicit SwitchIsolateScope(Isolate* new_isolate)
-      : new_isolate_(new_isolate),
-        saved_isolate_(Isolate::Current()),
-        saved_stack_limit_(saved_isolate_
-                           ? saved_isolate_->saved_stack_limit() : 0) {
-    // TODO(koda): Audit users; why would these two ever be equal?
-    if (saved_isolate_ != new_isolate_) {
-      if (new_isolate_ == NULL) {
-        Thread::ExitIsolate();
-      } else {
-        Thread::EnterIsolate(new_isolate_);
-        // Don't allow dart code to execute.
-        new_isolate_->SetStackLimit(~static_cast<uword>(0));
-      }
-    }
-  }
-
-  ~SwitchIsolateScope() {
-    if (saved_isolate_ != new_isolate_) {
-      if (new_isolate_ != NULL) {
-        Thread::ExitIsolate();
-      }
-      if (saved_isolate_ != NULL) {
-        Thread::EnterIsolate(saved_isolate_);
-        saved_isolate_->SetStackLimit(saved_stack_limit_);
-      }
-    }
-  }
-
- private:
-  Isolate* new_isolate_;
-  Isolate* saved_isolate_;
-  uword saved_stack_limit_;
-
-  DISALLOW_COPY_AND_ASSIGN(SwitchIsolateScope);
-};
-
 
 class IsolateSpawnState {
  public:

runtime/vm/service_isolate.cc

@@ -360,11 +360,8 @@ class RunServiceTask : public ThreadPool::Task {
       }
       Dart::RunShutdownCallback();
     }
-    {
-      // Shut the isolate down.
-      SwitchIsolateScope switch_scope(I);
-      Dart::ShutdownIsolate();
-    }
+    // Shut the isolate down.
+    Dart::ShutdownIsolate(I);
     if (FLAG_trace_service) {
       OS::Print("vm-service: Shutdown.\n");
     }