// Copyright 2012 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "src/base/once.h"
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#ifdef _WIN32
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#include <windows.h>
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#else
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#include <sched.h>
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#endif
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#include "src/base/atomicops.h"
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namespace v8 {
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namespace base {
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void CallOnceImpl(OnceType* once, std::function<void()> init_func) {
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AtomicWord state = Acquire_Load(once);
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// Fast path. The provided function was already executed.
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if (state == ONCE_STATE_DONE) {
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return;
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}
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// The function execution did not complete yet. The once object can be in one
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// of the two following states:
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// - UNINITIALIZED: We are the first thread calling this function.
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// - EXECUTING_FUNCTION: Another thread is already executing the function.
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//
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// First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION
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// atomically.
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state = Acquire_CompareAndSwap(
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once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION);
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if (state == ONCE_STATE_UNINITIALIZED) {
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// We are the first thread to call this function, so we have to call the
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// function.
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init_func();
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Release_Store(once, ONCE_STATE_DONE);
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} else {
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// Another thread has already started executing the function. We need to
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// wait until it completes the initialization.
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while (state == ONCE_STATE_EXECUTING_FUNCTION) {
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#ifdef _WIN32
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::Sleep(0);
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#else
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sched_yield();
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#endif
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state = Acquire_Load(once);
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}
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}
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}
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} // namespace base
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} // namespace v8
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