Refactor lazy_instance to avoid a strict aliasing problem with gcc 4.4.

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/dynamic_annotations.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);
-
-    // See the comment to the corresponding HAPPENS_AFTER in Pointer().
-    ANNOTATE_HAPPENS_BEFORE(&state_);
-
-    // Instance is created, go from CREATING to CREATED.
-    base::subtle::Release_Store(&state_, STATE_CREATED);
-
-    // Allow reusing the LazyInstance (reset it to the initial state). This
-    // makes possible calling all AtExit callbacks between tests. Assumes that
-    // no other threads execute when AtExit callbacks are processed.
-    base::AtExitManager::RegisterCallback(&LazyInstanceHelper::ResetState,
-                                          this);
-
-    // Make sure that the lazily instantiated object will get destroyed at exit.
-    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();
-  }
-}
-
-// static
-void LazyInstanceHelper::ResetState(void* helper) {
-  reinterpret_cast<LazyInstanceHelper*>(helper)->state_ = STATE_EMPTY;
-}
-
-}  // namespace base