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

src/cpu-profiler.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 501 matching lines @@
         FLAG_log_code = saved_log_code_flag;
       }
       isolate->logger()->LogCompiledFunctions();
       isolate->logger()->LogAccessorCallbacks();
     }
     // Enable stack sampling.
     if (!sampler->IsActive()) {
       sampler->Start();
       need_to_stop_sampler_ = true;
     }
+    sampler->SetHasProcessingThread(true);
     sampler->IncreaseProfilingDepth();
     processor_->Start();
   }
 }
 
 
 CpuProfile* CpuProfiler::StopCollectingProfile(const char* title) {
   const double actual_sampling_rate = generator_->actual_sampling_rate();
   StopProcessorIfLastProfile(title);
   CpuProfile* result =
@@ skipping 22 matching lines @@
 }
 
 
 void CpuProfiler::StopProcessor() {
   NoBarrier_Store(&is_profiling_, false);
   processor_->Stop();
   processor_->Join();
   Logger* logger = Isolate::Current()->logger();
   Sampler* sampler = logger->sampler();
   sampler->DecreaseProfilingDepth();
+  sampler->SetHasProcessingThread(false);
   if (need_to_stop_sampler_) {
     sampler->Stop();
     need_to_stop_sampler_ = false;
   }
   delete processor_;
   delete generator_;
   processor_ = NULL;
   generator_ = NULL;
   logger->logging_nesting_ = saved_logging_nesting_;
 }
 
 
 void CpuProfiler::SetUp() {
   Isolate* isolate = Isolate::Current();
   if (isolate->cpu_profiler() == NULL) {
     isolate->set_cpu_profiler(new CpuProfiler());
   }
 }
 
 
 void CpuProfiler::TearDown() {
   Isolate* isolate = Isolate::Current();
   if (isolate->cpu_profiler() != NULL) {
     delete isolate->cpu_profiler();
   }
   isolate->set_cpu_profiler(NULL);
 }
 
 } }  // namespace v8::internal