Make adding a pending deopt atomic.

runtime/vm/isolate.h

 // 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.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 386 matching lines @@
     return shutdown_callback_;
   }
 
   void set_object_id_ring(ObjectIdRing* ring) {
     object_id_ring_ = ring;
   }
   ObjectIdRing* object_id_ring() {
     return object_id_ring_;
   }
 
-  MallocGrowableArray<PendingLazyDeopt>* pending_deopts() {
+  void AddPendingDeopt(uword fp, uword pc);
+  uword FindPendingDeopt(uword fp) const;
+  void ClearPendingDeoptsAtOrBelow(uword fp) const;

[siva, 2016/10/10 04:10:26]

This function is marked as const but it seems to modify pending_deopts_ how come
the compiler is not complaining.

+  MallocGrowableArray<PendingLazyDeopt>* pending_deopts() const {
     return pending_deopts_;
   }
   bool IsDeoptimizing() const { return deopt_context_ != NULL; }
   DeoptContext* deopt_context() const { return deopt_context_; }
   void set_deopt_context(DeoptContext* value) {
     ASSERT(value == NULL || deopt_context_ == NULL);
     deopt_context_ = value;
   }
 
   BackgroundCompiler* background_compiler() const {
@@ skipping 590 matching lines @@
   intptr_t* spawn_count_;
 
   Dart_IsolateFlags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_