Lazily initialize thread pool to avoid allocating all the threads during startup

src/libplatform/default-platform.cc

 // Copyright 2013 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 22 matching lines @@
 #include "../checks.h"
 // TODO(jochen): Why is cpu.h not in platform/?
 #include "../cpu.h"
 #include "worker-thread.h"
 
 namespace v8 {
 namespace internal {
 
 
 DefaultPlatform::DefaultPlatform()
-    : initialized_(false) {}
+    : initialized_(false), thread_pool_size_(0) {}
 
 
 DefaultPlatform::~DefaultPlatform() {
   LockGuard<Mutex> guard(&lock_);
   if (initialized_) {
     queue_.Terminate();
     for (std::vector<WorkerThread*>::iterator i = thread_pool_.begin();
          i != thread_pool_.end(); ++i) {
       delete *i;
     }
   }
 }
 
 
 void DefaultPlatform::SetThreadPoolSize(int thread_pool_size) {
   LockGuard<Mutex> guard(&lock_);
   ASSERT(thread_pool_size >= 0);
+  if (thread_pool_size < 1)
+    thread_pool_size = CPU::NumberOfProcessorsOnline();
+  thread_pool_size_ = Max(Min(thread_pool_size, kMaxThreadPoolSize), 1);
+}
+
+
+void DefaultPlatform::EnsureInitialized() {
+  LockGuard<Mutex> guard(&lock_);
   if (initialized_) return;
   initialized_ = true;
-  if (thread_pool_size < 1)
-    thread_pool_size = CPU::NumberOfProcessorsOnline();
-  thread_pool_size = Max(Min(thread_pool_size, kMaxThreadPoolSize), 1);
 
-  for (int i = 0; i < thread_pool_size; ++i)
+  for (int i = 0; i < thread_pool_size_; ++i)
     thread_pool_.push_back(new WorkerThread(&queue_));
 }
 
 void DefaultPlatform::CallOnBackgroundThread(Task *task,
                                              ExpectedRuntime expected_runtime) {
-#ifdef DEBUG
-  {
-    LockGuard<Mutex> guard(&lock_);
-    ASSERT(initialized_);
-  }
-#endif
+  EnsureInitialized();
   queue_.Append(task);
 }
 
 
 void DefaultPlatform::CallOnForegroundThread(v8::Isolate* isolate, Task* task) {
   // TODO(jochen): implement.
   task->Run();
   delete task;
 }
 
 } }  // namespace v8::internal