Use mutex instead of busy wait when installing optimized function.

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 71 matching lines @@
   OptimizingCompiler* optimizing_compiler = NULL;
   input_queue_.Dequeue(&optimizing_compiler);
   Barrier_AtomicIncrement(&queue_length_, static_cast<Atomic32>(-1));
 
   // The function may have already been optimized by OSR.  Simply continue.
   OptimizingCompiler::Status status = optimizing_compiler->OptimizeGraph();
   USE(status);   // Prevent an unused-variable error in release mode.
   ASSERT(status != OptimizingCompiler::FAILED);
 
   // The function may have already been optimized by OSR.  Simply continue.
-  // Mark it for installing before queuing so that we can be sure of the write
-  // order: marking first and (after being queued) installing code second.
+  // Use a mutex to make sure that functions marked for install
+  // are always also queued.
+  ScopedLock mark_and_queue(install_mutex_);
   { Heap::RelocationLock relocation_lock(isolate_->heap());
     AllowHandleDereference ahd;
     optimizing_compiler->info()->closure()->MarkForInstallingRecompiledCode();
   }
   output_queue_.Enqueue(optimizing_compiler);
 }
 
 
 void OptimizingCompilerThread::Stop() {
   ASSERT(!IsOptimizerThread());
@@ skipping 16 matching lines @@
     double total_time = static_cast<double>(time_spent_total_);
     double percentage = (compile_time * 100) / total_time;
     PrintF("  ** Compiler thread did %.2f%% useful work\n", percentage);
   }
 }
 
 
 void OptimizingCompilerThread::InstallOptimizedFunctions() {
   ASSERT(!IsOptimizerThread());
   HandleScope handle_scope(isolate_);
-  int functions_installed = 0;
   OptimizingCompiler* compiler;
-  while (output_queue_.Dequeue(&compiler)) {
+  while (true) {
+    { // Memory barrier to ensure marked functions are queued.
+      ScopedLock marked_and_queued(install_mutex_);
+      if (!output_queue_.Dequeue(&compiler)) return;
+    }
     Compiler::InstallOptimizedCode(compiler);
-    functions_installed++;
   }
 }
 
 
 void OptimizingCompilerThread::QueueForOptimization(
     OptimizingCompiler* optimizing_compiler) {
   ASSERT(IsQueueAvailable());
   ASSERT(!IsOptimizerThread());
   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;
   return ThreadId::Current().ToInteger() == thread_id_;
 }
 #endif
 
 
 } }  // namespace v8::internal