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