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// 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 {
bool LazyInstanceHelper::NeedsInstance() {
// 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) {
// Caller must create instance
return true;
} else {
// It's either in the process of being created, or already created. Spin.
while (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED)
PlatformThread::YieldCurrentThread();
}
// Someone else created the instance.
return false;
}
void LazyInstanceHelper::CompleteInstance(void* instance, void (*dtor)(void*)) {
// 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);
}
// static
void LazyInstanceHelper::ResetState(void* helper) {
reinterpret_cast<LazyInstanceHelper*>(helper)->state_ = STATE_EMPTY;
}
} // namespace base
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