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// Copyright 2012 the V8 project 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 "src/base/once.h"
#ifdef _WIN32
#include <windows.h>
#else
#include <sched.h>
#endif
namespace v8 {
namespace base {
void CallOnceImpl(OnceType* once, std::function<void()> init_func) {
// Fast path. The provided function was already executed.
if (once->load(std::memory_order_acquire) == ONCE_STATE_DONE) {
return;
}
// The function execution did not complete yet. The once object can be in one
// of the two following states:
// - UNINITIALIZED: We are the first thread calling this function.
// - EXECUTING_FUNCTION: Another thread is already executing the function.
//
// First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION
// atomically.
uint8_t expected = ONCE_STATE_UNINITIALIZED;
if (once->compare_exchange_strong(expected, ONCE_STATE_EXECUTING_FUNCTION,
std::memory_order_acq_rel)) {
// We are the first thread to call this function, so we have to call the
// function.
init_func();
once->store(ONCE_STATE_DONE, std::memory_order_release);
} else {
// Another thread has already started executing the function. We need to
// wait until it completes the initialization.
while (once->load(std::memory_order_acquire) ==
ONCE_STATE_EXECUTING_FUNCTION) {
#ifdef _WIN32
::Sleep(0);
#else
sched_yield();
#endif
}
}
}
} // namespace base
} // namespace v8
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