| 1 | //===----------------------------------------------------------------------===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #include <__config> |
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| 10 | #include <__mutex/once_flag.h> |
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| 11 | #include <__utility/exception_guard.h> |
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| 12 | |
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| 13 | #if _LIBCPP_HAS_THREADS |
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| 14 | # include <__thread/support.h> |
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| 15 | #endif |
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| 16 | |
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| 17 | #include "include/atomic_support.h" |
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| 18 | |
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| 19 | _LIBCPP_BEGIN_NAMESPACE_STD |
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| 20 | |
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| 21 | // If dispatch_once_f ever handles C++ exceptions, and if one can get to it |
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| 22 | // without illegal macros (unexpected macros not beginning with _UpperCase or |
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| 23 | // __lowercase), and if it stops spinning waiting threads, then call_once should |
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| 24 | // call into dispatch_once_f instead of here. Relevant radar this code needs to |
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| 25 | // keep in sync with: 7741191. |
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| 26 | |
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| 27 | #if _LIBCPP_HAS_THREADS |
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| 28 | static constinit __libcpp_mutex_t mut = _LIBCPP_MUTEX_INITIALIZER; |
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| 29 | static constinit __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER; |
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| 30 | #endif |
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| 31 | |
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| 32 | void __call_once(volatile once_flag::_State_type& flag, void* arg, void (*func)(void*)) { |
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| 33 | #if !_LIBCPP_HAS_THREADS |
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| 34 | |
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| 35 | if (flag == once_flag::_Unset) { |
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| 36 | auto guard = std::__make_exception_guard(ex: [&flag] { flag = once_flag::_Unset; }); |
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| 37 | flag = once_flag::_Pending; |
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| 38 | func(arg); |
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| 39 | flag = once_flag::_Complete; |
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| 40 | guard.__complete(); |
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| 41 | } |
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| 42 | |
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| 43 | #else // !_LIBCPP_HAS_THREADS |
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| 44 | |
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| 45 | __libcpp_mutex_lock(&mut); |
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| 46 | while (flag == once_flag::_Pending) |
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| 47 | __libcpp_condvar_wait(&cv, &mut); |
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| 48 | if (flag == once_flag::_Unset) { |
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| 49 | auto guard = std::__make_exception_guard([&flag] { |
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| 50 | __libcpp_mutex_lock(&mut); |
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| 51 | __libcpp_relaxed_store(&flag, once_flag::_Unset); |
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| 52 | __libcpp_mutex_unlock(&mut); |
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| 53 | __libcpp_condvar_broadcast(&cv); |
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| 54 | }); |
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| 55 | |
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| 56 | __libcpp_relaxed_store(&flag, once_flag::_Pending); |
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| 57 | __libcpp_mutex_unlock(&mut); |
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| 58 | func(arg); |
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| 59 | __libcpp_mutex_lock(&mut); |
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| 60 | __libcpp_atomic_store(&flag, once_flag::_Complete, _AO_Release); |
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| 61 | __libcpp_mutex_unlock(&mut); |
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| 62 | __libcpp_condvar_broadcast(&cv); |
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| 63 | guard.__complete(); |
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| 64 | } else { |
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| 65 | __libcpp_mutex_unlock(&mut); |
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| 66 | } |
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| 67 | |
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| 68 | #endif // !_LIBCPP_HAS_THREADS |
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| 69 | } |
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| 70 | |
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| 71 | _LIBCPP_END_NAMESPACE_STD |
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| 72 | |
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