Merge changes from bleeding_edge into experimental toiger branch....

src/v8threads.h

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 69 matching lines @@
  private:
   static void EagerlyArchiveThread();
 
   static Mutex* mutex_;
   static ThreadHandle mutex_owner_;
   static ThreadHandle lazily_archived_thread_;
   static ThreadState* lazily_archived_thread_state_;
 };
 
 
+// The ContextSwitcher thread is used to schedule regular preemptions to
+// multiple running V8 threads. Generally it is necessary to call
+// StartPreemption if there is more than one thread running. If not, a single
+// JavaScript can take full control of V8 and not allow other threads to run.
 class ContextSwitcher: public Thread {
  public:
-  void Run();
+  // Set the preemption interval for the ContextSwitcher thread.
   static void StartPreemption(int every_n_ms);
+
+  // Stop sending preemption requests to threads.
   static void StopPreemption();
+
+  // Preempted thread needs to call back to the ContextSwitcher to acknowlege
+  // the handling of a preemption request.
   static void PreemptionReceived();
+
  private:
   explicit ContextSwitcher(int every_n_ms);
-  void WaitForPreemption();
-  void Stop();
-  Semaphore* preemption_semaphore_;
+
+  void Run();
+
   bool keep_going_;
   int sleep_ms_;
+
+  static ContextSwitcher* singleton_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8THREADS_H_