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

src/platform-macos.cc

 // 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 801 matching lines @@
     sampler_thread->SampleContext(sampler);
   }
 
   static void DoRuntimeProfile(Sampler* sampler, void* ignored) {
     if (!sampler->isolate()->IsInitialized()) return;
     sampler->isolate()->runtime_profiler()->NotifyTick();
   }
 
   void SampleContext(Sampler* sampler) {
     thread_act_t profiled_thread = sampler->platform_data()->profiled_thread();
-    TickSample* sample = CpuProfiler::StartTickSampleEvent(sampler->isolate());
-    if (sample == NULL) return;
+    TickSample sample_obj;
+    TickSample* sample = CpuProfiler::StartTickSampleEvent(isolate);
+    if (sample == NULL) sample = &sample_obj;
+
 
     if (KERN_SUCCESS != thread_suspend(profiled_thread)) return;
 
 #if V8_HOST_ARCH_X64
     thread_state_flavor_t flavor = x86_THREAD_STATE64;
     x86_thread_state64_t state;
     mach_msg_type_number_t count = x86_THREAD_STATE64_COUNT;
 #if __DARWIN_UNIX03
 #define REGISTER_FIELD(name) __r ## name
 #else
@@ skipping 88 matching lines @@
 }
 
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SamplerThread::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 
+void Sampler::StartSampling() {
+}
+
+
+void Sampler::StopSampling() {
+}
+
+
 } }  // namespace v8::internal