Send SIGPROF signals on the profiler event processor thread

src/platform.h

Index: src/platform.h
diff --git a/src/platform.h b/src/platform.h
index 56ac61dc7b6352a7323710daf5fd2c7445d28ef4..5fde6a009aa40a01e548429894810de9a45b5b90 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -766,10 +766,17 @@ class 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_);
+  }
+  void IncreaseProfilingDepth() {
+    if (NoBarrier_AtomicIncrement(&profiling_, 1) == 1) StartProfiling();
+  }
+  void DecreaseProfilingDepth() {
+    if (!NoBarrier_AtomicIncrement(&profiling_, -1)) StopProfiling();
+  }
 
   // Whether the sampler is running (that is, consumes resources).
   bool IsActive() const { return NoBarrier_Load(&active_); }
@@ -785,6 +792,14 @@ class Sampler {
 
   PlatformData* platform_data() { return data_; }
 
+  // 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);
+  }
+
  protected:
   virtual void DoSampleStack(TickSample* sample) = 0;
 
@@ -792,9 +807,15 @@ class Sampler {
   void SetActive(bool value) { NoBarrier_Store(&active_, value); }
   void IncSamplesTaken() { if (++samples_taken_ < 0) samples_taken_ = 0; }
 
+  // Perform platform-specific initialization before DoSample() may be invoked.
+  void StartProfiling();
+  // Perform platform-specific cleanup after profiling.
+  void StopProfiling();
+
   Isolate* isolate_;
   const int interval_;
   Atomic32 profiling_;
+  Atomic32 has_processing_thread_;
   Atomic32 active_;
   PlatformData* data_;  // Platform specific data.
   int samples_taken_;  // Counts stack samples taken.