Enable iterating over roots from helper threads by moving stack walking.

runtime/vm/thread_registry.h

 // Copyright (c) 2015, 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.
 
 #ifndef VM_THREAD_REGISTRY_H_
 #define VM_THREAD_REGISTRY_H_
 
 #include "vm/globals.h"
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
+#include "vm/stack_frame.h"
 #include "vm/thread.h"
 
 namespace dart {
 
 // Unordered collection of threads relating to a particular isolate.
 class ThreadRegistry {
  public:
   ThreadRegistry()
       : monitor_(new Monitor()),
         entries_(),
@@ skipping 89 matching lines @@
                entry.thread,
                entry.thread->isolate());
       }
     }
   }
 
   void VisitObjectPointers(ObjectPointerVisitor* visitor) {
     MonitorLocker ml(monitor_);
     for (int i = 0; i < entries_.length(); ++i) {
       const Entry& entry = entries_[i];
-      Zone* zone = entry.scheduled ? entry.thread->zone() : entry.state.zone;
-      if (zone != NULL) {
-        zone->VisitObjectPointers(visitor);
+      const Thread::State& state =
+          entry.scheduled ? entry.thread->state_ : entry.state;
+      if (state.zone != NULL) {
+        state.zone->VisitObjectPointers(visitor);
+      }
+      // Iterate over all the stack frames and visit objects on the stack.
+      uword efi = state.top_exit_frame_info;
+      if (efi == 0) continue;
+      StackFrameIterator frames_iterator(efi, false);

[Ivan Posva, 2015/08/11 17:41:31]

Please do not use explicit constants and use the appropriately named constant
StackFrameIterator::kDontValidateFrames.

+      StackFrame* frame = frames_iterator.NextFrame();
+      while (frame != NULL) {
+        frame->VisitObjectPointers(visitor);
+        frame = frames_iterator.NextFrame();
       }
     }
   }
 
  private:
   struct Entry {
     Thread* thread;
     bool scheduled;
     Thread::State state;
   };
@@ skipping 25 matching lines @@
   intptr_t remaining_;    // Number of threads yet to reach their safepoint.
   int64_t round_;         // Counter, to prevent missing updates to remaining_
                           // (see comments in CheckSafepointLocked).
 
   DISALLOW_COPY_AND_ASSIGN(ThreadRegistry);
 };
 
 }  // namespace dart
 
 #endif  // VM_THREAD_REGISTRY_H_