Fix crash in code coverage generation.

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 1415 matching lines @@
 void Isolate::Shutdown() {
   ASSERT(this == Isolate::Current());
   ASSERT(top_resource() == NULL);
 #if defined(DEBUG)
   if (heap_ != NULL) {
     // The VM isolate keeps all objects marked.
     heap_->Verify(this == Dart::vm_isolate() ? kRequireMarked : kForbidMarked);
   }
 #endif  // DEBUG
 
+  // 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.
+    StackZone stack_zone(this);
+    HandleScope handle_scope(this);
+
+    // Write out the coverage data if collection has been enabled.
+    CodeCoverage::Write(this);
+
+    if ((timeline_event_recorder_ != NULL) &&
+        (FLAG_timeline_trace_dir != NULL)) {
+      timeline_event_recorder_->WriteTo(FLAG_timeline_trace_dir);
+    }
+  }
+
   // Remove this isolate from the list *before* we start tearing it down, to
   // avoid exposing it in a state of decay.
   RemoveIsolateFromList(this);
 
   if (heap_ != NULL) {
     // Wait for any concurrent GC tasks to finish before shutting down.
+    // TODO(koda): Support faster sweeper shutdown (e.g., after current page).
     PageSpace* old_space = heap_->old_space();
     MonitorLocker ml(old_space->tasks_lock());
     while (old_space->tasks() > 0) {
       ml.Wait();
     }
   }
 
-  // Create an area where we do have a zone and a handle scope so that we can
-  // call VM functions while tearing this isolate down.
+  // Then, proceed with low-level teardown.
   {
+    // Ensure we have a zone and handle scope so that we can call VM functions,
+    // but we no longer allocate new heap objects.
     StackZone stack_zone(this);
     HandleScope handle_scope(this);
+    NoSafepointScope no_safepoint_scope;
 
     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();
 
     // 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();
 
-    // Write out the coverage data if collection has been enabled.
-    CodeCoverage::Write(this);
-
     // Finalize any weak persistent handles with a non-null referent.
     FinalizeWeakPersistentHandlesVisitor visitor;
     api_state()->weak_persistent_handles().VisitHandles(&visitor);
     api_state()->prologue_weak_persistent_handles().VisitHandles(&visitor);
 
     if (FLAG_trace_isolates) {
       heap()->PrintSizes();
       megamorphic_cache_table()->PrintSizes();
       Symbols::DumpStats();
       OS::Print("[-] Stopping isolate:\n"
                 "\tisolate:    %s\n", name());
     }
+  }
 
-    if ((timeline_event_recorder_ != NULL) &&
-        (FLAG_timeline_trace_dir != NULL)) {
-      timeline_event_recorder_->WriteTo(FLAG_timeline_trace_dir);
-    }
+#if defined(DEBUG)
+  // No concurrent sweeper tasks should be running at this point.
+  if (heap_ != NULL) {
+    PageSpace* old_space = heap_->old_space();
+    MonitorLocker ml(old_space->tasks_lock());
+    ASSERT(old_space->tasks() == 0);
   }
+#endif
 
   // TODO(5411455): For now just make sure there are no current isolates
   // as we are shutting down the isolate.
   Thread::ExitIsolate();
   // All threads should have exited by now.
   thread_registry()->CheckNotScheduled(this);
   Profiler::ShutdownProfilingForIsolate(this);
 }
 
 
@@ skipping 590 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart