Create a LazyInstance abstraction.

base/lazy_instance.cc

+// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/lazy_instance.h"
+
+#include "base/at_exit.h"
+#include "base/atomicops.h"
+#include "base/basictypes.h"
+#include "base/platform_thread.h"
+
+namespace base {
+
+void LazyInstanceHelper::EnsureInstance(void* instance,
+                                        void (*ctor)(void*),
+                                        void (*dtor)(void*)) {
+  // Try to create the instance, if we're the first, will go from EMPTY
+  // to CREATING, otherwise we've already been beaten here.
+  if (base::subtle::Acquire_CompareAndSwap(
+          &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) {
+    // Created the instance in the space provided by |instance|.
+    ctor(instance);
+    // Instance is created, go from CREATING to CREATED.
+    base::subtle::Release_Store(&state_, STATE_CREATED);
+    // Register the destructor callback with AtExitManager.
+    base::AtExitManager::RegisterCallback(dtor, instance);
+  } else {
+    // It's either in the process of being created, or already created.  Spin.
+    while (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED)
+      PlatformThread::YieldCurrentThread();
+  }
+}
+
+}  // namespace base