Perform CPU sampling by CPU sampling thread only iff processing thread is not running.

src/platform.h

 // Copyright 2012 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 742 matching lines @@
   void DoSample();
 
   // This method is called for each sampling period with the current
   // program counter.
   virtual void Tick(TickSample* sample) = 0;
 
   // Start and stop sampler.
   void Start();
   void Stop();
 
-  // Is the sampler used for profiling?
-  bool IsProfiling() const { return NoBarrier_Load(&profiling_) > 0; }
-  void IncreaseProfilingDepth() { NoBarrier_AtomicIncrement(&profiling_, 1); }
-  void DecreaseProfilingDepth() { NoBarrier_AtomicIncrement(&profiling_, -1); }
+  // Whether the sampling thread should use this Sampler for CPU profiling?
+  bool IsProfiling() const {
+    return NoBarrier_Load(&profiling_) > 0 &&
+        !NoBarrier_Load(&has_processing_thread_);
+  }
+  // Perform platform-specific initialization before DoSample() may be invoked.
+  void StartSampling();
+  // Perform platform-specific cleanup after samping.
+  void StopSampling();
+  void IncreaseProfilingDepth() {
+    if (NoBarrier_AtomicIncrement(&profiling_, 1) == 1) {
+      StartSampling();
+    }
+  }
+  void DecreaseProfilingDepth() {
+    if (!NoBarrier_AtomicIncrement(&profiling_, -1)) {
+      StopSampling();
+    }
+  }
+  void SetHasProcessingThread(bool value) {
+    NoBarrier_Store(&has_processing_thread_, value);
+  }
 
   // Whether the sampler is running (that is, consumes resources).
   bool IsActive() const { return NoBarrier_Load(&active_); }
 
   Isolate* isolate() { return isolate_; }
 
   // Used in tests to make sure that stack sampling is performed.
   int samples_taken() const { return samples_taken_; }
   void ResetSamplesTaken() { samples_taken_ = 0; }
 
   class PlatformData;
   PlatformData* data() { return data_; }
 
   PlatformData* platform_data() { return data_; }
 
  protected:
   virtual void DoSampleStack(TickSample* sample) = 0;
 
  private:
   void SetActive(bool value) { NoBarrier_Store(&active_, value); }
   void IncSamplesTaken() { if (++samples_taken_ < 0) samples_taken_ = 0; }
 
   Isolate* isolate_;
   const int interval_;
   Atomic32 profiling_;
   Atomic32 active_;
+  Atomic32 has_processing_thread_;
   PlatformData* data_;  // Platform specific data.
   int samples_taken_;  // Counts stack samples taken.
   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_PLATFORM_H_