Fixes crashes in VM isolate shutdown.

runtime/vm/isolate.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/json.h"
 #include "vm/code_observers.h"
@@ skipping 500 matching lines @@
 
 bool IsolateMessageHandler::ProcessUnhandledException(const Error& result) {
   // Notify the debugger about specific unhandled exceptions which are withheld
   // when being thrown.
   if (result.IsUnhandledException()) {
     const UnhandledException& error = UnhandledException::Cast(result);
     RawInstance* exception = error.exception();
     if ((exception == I->object_store()->out_of_memory()) ||
         (exception == I->object_store()->stack_overflow())) {
       // We didn't notify the debugger when the stack was full. Do it now.
+      ASSERT(I->debugger() != NULL);
       I->debugger()->SignalExceptionThrown(Instance::Handle(exception));
     }
   }
 
   // Invoke the isolate's unhandled exception callback if there is one.
   if (Isolate::UnhandledExceptionCallback() != NULL) {
     Dart_EnterScope();
     Dart_Handle error = Api::NewHandle(I, result.raw());
     (Isolate::UnhandledExceptionCallback())(error);
     Dart_ExitScope();
@@ skipping 237 matching lines @@
 #if defined(DEBUG)
   // Verify that we are never reusing a live origin id.
   VerifyOriginId id_verifier(result->main_port());
   Isolate::VisitIsolates(&id_verifier);
 #endif
   result->set_origin_id(result->main_port());
   result->set_pause_capability(result->random()->NextUInt64());
   result->set_terminate_capability(result->random()->NextUInt64());
 
   result->BuildName(name_prefix);
-  result->debugger_ = new Debugger();
-  result->debugger_->Initialize(result);
+  if (!is_vm_isolate) {
+    result->debugger_ = new Debugger();
+    result->debugger_->Initialize(result);
+  }
   if (FLAG_trace_isolates) {
     if (name_prefix == NULL || strcmp(name_prefix, "vm-isolate") != 0) {
       OS::Print("[+] Starting isolate:\n"
                 "\tisolate:    %s\n", result->name());
     }
   }
   if (FLAG_compiler_stats) {
     result->compiler_stats_ = new CompilerStats(result);
   }
   ObjectIdRing::Init(result);
@@ skipping 424 matching lines @@
     Function& func = Function::Handle(isolate);
     func ^= result.raw();
 
     // TODO(turnidge): Currently we need a way to force a one-time
     // breakpoint for all spawned isolates to support isolate
     // debugging.  Remove this once the vmservice becomes the standard
     // way to debug. Set the breakpoint on the static function instead
     // of its implicit closure function because that latter is merely
     // a dispatcher that is marked as undebuggable.
     if (FLAG_break_at_isolate_spawn) {
+      ASSERT(isolate->debugger() != NULL);
       isolate->debugger()->OneTimeBreakAtEntry(func);
     }
 
     func = func.ImplicitClosureFunction();
 
     const Array& capabilities = Array::Handle(Array::New(2));
     Capability& capability = Capability::Handle();
     capability = Capability::New(isolate->pause_capability());
     capabilities.SetAt(0, capability);
     // Check whether this isolate should be started in paused state.
@@ skipping 184 matching lines @@
     if (compiler_stats_ != NULL) {
       compiler_stats()->Print();
     }
 
     // Notify exit listeners that this isolate is shutting down.
     if (object_store() != NULL) {
       NotifyExitListeners();
     }
 
     // Clean up debugger resources.
-    debugger()->Shutdown();
+    if (debugger() != NULL) {
+      debugger()->Shutdown();
+    }
 
     // Close all the ports owned by this isolate.
     PortMap::ClosePorts(message_handler());
 
     // Fail fast if anybody tries to post any more messsages to this isolate.
     delete message_handler();
     set_message_handler(NULL);
 
     // Dump all accumulated timer data for the isolate.
     timer_list_.ReportTimers();
@@ skipping 80 matching lines @@
   visitor->VisitPointer(reinterpret_cast<RawObject**>(&default_tag_));
 
   // Visit the tag table which is stored in the isolate.
   visitor->VisitPointer(reinterpret_cast<RawObject**>(&tag_table_));
 
   // Visit the deoptimized code array which is stored in the isolate.
   visitor->VisitPointer(
       reinterpret_cast<RawObject**>(&deoptimized_code_array_));
 
   // Visit objects in the debugger.
+  ASSERT(debugger() != NULL);

[Ivan Posva, 2015/06/16 16:31:15]

if (debugger() != NULL) {
  ...
}

Since we are visiting the VM isolate in certain situations.

   debugger()->VisitObjectPointers(visitor);
 
   // Visit objects that are being used for deoptimization.
   if (deopt_context() != NULL) {
     deopt_context()->VisitObjectPointers(visitor);
   }
 }
 
 
 void Isolate::VisitWeakPersistentHandles(HandleVisitor* visitor,
@@ skipping 36 matching lines @@
   }
   {
     JSONObject jsheap(&jsobj, "_heaps");
     heap()->PrintToJSONObject(Heap::kNew, &jsheap);
     heap()->PrintToJSONObject(Heap::kOld, &jsheap);
   }
 
   jsobj.AddProperty("livePorts", message_handler()->live_ports());
   jsobj.AddProperty("pauseOnExit", message_handler()->pause_on_exit());
 
+  ASSERT(debugger() != NULL);

[Ivan Posva, 2015/06/16 16:31:15]

We should allow printing of the VM isolate.

   if (message_handler()->paused_on_start()) {
     ASSERT(debugger()->PauseEvent() == NULL);
     ServiceEvent pause_event(this, ServiceEvent::kPauseStart);
     jsobj.AddProperty("pauseEvent", &pause_event);
   } else if (message_handler()->paused_on_exit()) {
     ASSERT(debugger()->PauseEvent() == NULL);
     ServiceEvent pause_event(this, ServiceEvent::kPauseExit);
     jsobj.AddProperty("pauseEvent", &pause_event);
   } else if (debugger()->PauseEvent() != NULL) {
     ServiceEvent pause_event(debugger()->PauseEvent());
@@ skipping 431 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart