Avoid data race in debug mode on the parallel thread.

src/optimizing-compiler-thread.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 21 matching lines @@
 #include "hydrogen.h"
 #include "isolate.h"
 #include "v8threads.h"
 
 namespace v8 {
 namespace internal {
 
 
 void OptimizingCompilerThread::Run() {
 #ifdef DEBUG
-  thread_id_ = ThreadId::Current().ToInteger();
+  { ScopedLock lock(thread_id_mutex_);
+    thread_id_ = ThreadId::Current().ToInteger();
+  }
 #endif
   Isolate::SetIsolateThreadLocals(isolate_, NULL);
   DisallowHeapAllocation no_allocation;
   DisallowHandleAllocation no_handles;
   DisallowHandleDereference no_deref;
 
   int64_t epoch = 0;
   if (FLAG_trace_parallel_recompilation) epoch = OS::Ticks();
 
   while (true) {
@@ skipping 96 matching lines @@
   Barrier_AtomicIncrement(&queue_length_, static_cast<Atomic32>(1));
   optimizing_compiler->info()->closure()->MarkInRecompileQueue();
   input_queue_.Enqueue(optimizing_compiler);
   input_queue_semaphore_->Signal();
 }
 
 
 #ifdef DEBUG
 bool OptimizingCompilerThread::IsOptimizerThread() {
   if (!FLAG_parallel_recompilation) return false;
+  ScopedLock lock(thread_id_mutex_);
   return ThreadId::Current().ToInteger() == thread_id_;
 }
 #endif
 
 
 } }  // namespace v8::internal