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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include <__mutex/once_flag.h>
#include <__utility/exception_guard.h>
#ifndef _LIBCPP_HAS_NO_THREADS
# include <__threading_support>
#endif
#include "include/atomic_support.h"
_LIBCPP_BEGIN_NAMESPACE_STD
// If dispatch_once_f ever handles C++ exceptions, and if one can get to it
// without illegal macros (unexpected macros not beginning with _UpperCase or
// __lowercase), and if it stops spinning waiting threads, then call_once should
// call into dispatch_once_f instead of here. Relevant radar this code needs to
// keep in sync with: 7741191.
#ifndef _LIBCPP_HAS_NO_THREADS
static constinit __libcpp_mutex_t mut = _LIBCPP_MUTEX_INITIALIZER;
static constinit __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER;
#endif
#ifdef _LIBCPP_ABI_MICROSOFT
void __call_once(volatile std::atomic<once_flag::_State_type>& flag, void* arg, void (*func)(void*))
#else
void __call_once(volatile once_flag::_State_type& flag, void* arg, void (*func)(void*))
#endif
{
#if defined(_LIBCPP_HAS_NO_THREADS)
if (flag == once_flag::_Unset) {
auto guard = std::__make_exception_guard([&flag] { flag = once_flag::_Unset; });
flag = once_flag::_Pending;
func(arg);
flag = once_flag::_Complete;
guard.__complete();
}
#else // !_LIBCPP_HAS_NO_THREADS
__libcpp_mutex_lock(&mut);
while (flag == once_flag::_Pending)
__libcpp_condvar_wait(&cv, &mut);
if (flag == once_flag::_Unset) {
auto guard = std::__make_exception_guard([&flag] {
__libcpp_mutex_lock(&mut);
# ifdef _LIBCPP_ABI_MICROSOFT
flag.store(once_flag::_Unset);
# else
__libcpp_relaxed_store(&flag, once_flag::_Unset);
# endif
__libcpp_mutex_unlock(&mut);
__libcpp_condvar_broadcast(&cv);
});
# ifdef _LIBCPP_ABI_MICROSOFT
flag.store(once_flag::_Pending, memory_order_relaxed);
# else
__libcpp_relaxed_store(&flag, once_flag::_Pending);
# endif
__libcpp_mutex_unlock(&mut);
func(arg);
__libcpp_mutex_lock(&mut);
# ifdef _LIBCPP_ABI_MICROSOFT
flag.store(once_flag::_Complete, memory_order_release);
# else
__libcpp_atomic_store(&flag, once_flag::_Complete, _AO_Release);
# endif
__libcpp_mutex_unlock(&mut);
__libcpp_condvar_broadcast(&cv);
guard.__complete();
} else {
__libcpp_mutex_unlock(&mut);
}
#endif // !_LIBCPP_HAS_NO_THREADS
}
_LIBCPP_END_NAMESPACE_STD
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