Support higher CPU profiler sampling rate on posix systems

src/sampler.h

Index: src/sampler.h
diff --git a/src/sampler.h b/src/sampler.h
index 80ccc087cadff8c17a0c73b8ce913836a1fc89e3..cd65b12238fd9a493f1fab31212968e1edc0d79b 100644
--- a/src/sampler.h
+++ b/src/sampler.h
@@ -94,14 +94,25 @@ class 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_;
@@ -125,6 +136,7 @@ class Sampler {
   Isolate* isolate_;
   const int interval_;
   Atomic32 profiling_;
+  Atomic32 has_processing_thread_;
   Atomic32 active_;
   PlatformData* data_;  // Platform specific data.
   bool is_counting_samples_;