Support higher CPU profiler sampling rate on posix systems

src/sampler.h

 // Copyright 2013 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 76 matching lines @@
   Isolate* isolate() const { return isolate_; }
   int interval() const { return interval_; }
 
   // Performs stack sampling.
   void SampleStack(const RegisterState& regs);
 
   // Start and stop sampler.
   void Start();
   void Stop();
 
-  // Is the sampler used for profiling?
-  bool IsProfiling() const { return NoBarrier_Load(&profiling_) > 0; }
+  // Whether the sampling thread should use this Sampler for CPU profiling?
+  bool IsProfiling() const {
+    return NoBarrier_Load(&profiling_) > 0 &&
+        !NoBarrier_Load(&has_processing_thread_);
+  }
   void IncreaseProfilingDepth() { NoBarrier_AtomicIncrement(&profiling_, 1); }
   void DecreaseProfilingDepth() { NoBarrier_AtomicIncrement(&profiling_, -1); }
 
   // Whether the sampler is running (that is, consumes resources).
   bool IsActive() const { return NoBarrier_Load(&active_); }
 
+  // If true next sample must be initiated on the profiler event processor
+  // thread right after latest sample is processed.
+  static bool CanSampleOnProfilerEventsProcessorThread();
+  void DoSample();
+  void SetHasProcessingThread(bool value) {
+    NoBarrier_Store(&has_processing_thread_, value);
+  }
+
   // Used in tests to make sure that stack sampling is performed.
   unsigned js_and_external_sample_count() const {
     return js_and_external_sample_count_;
   }
   void StartCountingSamples() {
       is_counting_samples_ = true;
       js_and_external_sample_count_ = 0;
   }
 
   class PlatformData;
   PlatformData* platform_data() const { return data_; }
 
  protected:
   // This method is called for each sampling period with the current
   // program counter.
   virtual void Tick(TickSample* sample) = 0;
 
  private:
   void SetActive(bool value) { NoBarrier_Store(&active_, value); }
 
   Isolate* isolate_;
   const int interval_;
   Atomic32 profiling_;
+  Atomic32 has_processing_thread_;
   Atomic32 active_;
   PlatformData* data_;  // Platform specific data.
   bool is_counting_samples_;
   // Counts stack samples taken in JS VM state.
   unsigned js_and_external_sample_count_;
   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SAMPLER_H_