72 lines · cpp
1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include <__config>10#include <__mutex/once_flag.h>11#include <__utility/exception_guard.h>12 13#if _LIBCPP_HAS_THREADS14# include <__thread/support.h>15#endif16 17#include "include/atomic_support.h"18 19_LIBCPP_BEGIN_NAMESPACE_STD20 21// If dispatch_once_f ever handles C++ exceptions, and if one can get to it22// without illegal macros (unexpected macros not beginning with _UpperCase or23// __lowercase), and if it stops spinning waiting threads, then call_once should24// call into dispatch_once_f instead of here. Relevant radar this code needs to25// keep in sync with: 7741191.26 27#if _LIBCPP_HAS_THREADS28static constinit __libcpp_mutex_t mut = _LIBCPP_MUTEX_INITIALIZER;29static constinit __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER;30#endif31 32void __call_once(volatile once_flag::_State_type& flag, void* arg, void (*func)(void*)) {33#if !_LIBCPP_HAS_THREADS34 35 if (flag == once_flag::_Unset) {36 auto guard = std::__make_exception_guard([&flag] { flag = once_flag::_Unset; });37 flag = once_flag::_Pending;38 func(arg);39 flag = once_flag::_Complete;40 guard.__complete();41 }42 43#else // !_LIBCPP_HAS_THREADS44 45 __libcpp_mutex_lock(&mut);46 while (flag == once_flag::_Pending)47 __libcpp_condvar_wait(&cv, &mut);48 if (flag == once_flag::_Unset) {49 auto guard = std::__make_exception_guard([&flag] {50 __libcpp_mutex_lock(&mut);51 __libcpp_relaxed_store(&flag, once_flag::_Unset);52 __libcpp_mutex_unlock(&mut);53 __libcpp_condvar_broadcast(&cv);54 });55 56 __libcpp_relaxed_store(&flag, once_flag::_Pending);57 __libcpp_mutex_unlock(&mut);58 func(arg);59 __libcpp_mutex_lock(&mut);60 __libcpp_atomic_store(&flag, once_flag::_Complete, _AO_Release);61 __libcpp_mutex_unlock(&mut);62 __libcpp_condvar_broadcast(&cv);63 guard.__complete();64 } else {65 __libcpp_mutex_unlock(&mut);66 }67 68#endif // !_LIBCPP_HAS_THREADS69}70 71_LIBCPP_END_NAMESPACE_STD72