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-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef _LIBCPP___ATOMIC_ATOMIC_SYNC_H
10 #define _LIBCPP___ATOMIC_ATOMIC_SYNC_H
11 
12 #include <__atomic/contention_t.h>
13 #include <__atomic/cxx_atomic_impl.h>
14 #include <__atomic/memory_order.h>
15 #include <__availability>
16 #include <__chrono/duration.h>
17 #include <__config>
18 #include <__memory/addressof.h>
19 #include <__thread/poll_with_backoff.h>
20 #include <__threading_support>
21 #include <__type_traits/decay.h>
22 #include <cstring>
23 
24 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
25 #  pragma GCC system_header
26 #endif
27 
28 _LIBCPP_BEGIN_NAMESPACE_STD
29 
30 #ifndef _LIBCPP_HAS_NO_THREADS
31 
32 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile*);
33 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile*);
34 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t __libcpp_atomic_monitor(void const volatile*);
35 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __libcpp_atomic_wait(void const volatile*, __cxx_contention_t);
36 
37 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile*);
38 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile*);
39 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t __libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*);
40 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t);
41 
42 template <class _Atp, class _Fn>
43 struct __libcpp_atomic_wait_backoff_impl {
44     _Atp* __a;
45     _Fn __test_fn;
46     _LIBCPP_AVAILABILITY_SYNC
47     _LIBCPP_HIDE_FROM_ABI bool operator()(chrono::nanoseconds __elapsed) const
48     {
49         if(__elapsed > chrono::microseconds(64))
50         {
51             auto const __monitor = std::__libcpp_atomic_monitor(__a);
52             if(__test_fn())
53                 return true;
54             std::__libcpp_atomic_wait(__a, __monitor);
55         }
56         else if(__elapsed > chrono::microseconds(4))
57             __libcpp_thread_yield();
58         else
59             {} // poll
60         return false;
61     }
62 };
63 
64 template <class _Atp, class _Fn>
65 _LIBCPP_AVAILABILITY_SYNC
66 _LIBCPP_HIDE_FROM_ABI bool __cxx_atomic_wait(_Atp* __a, _Fn && __test_fn)
67 {
68     __libcpp_atomic_wait_backoff_impl<_Atp, __decay_t<_Fn> > __backoff_fn = {__a, __test_fn};
69     return std::__libcpp_thread_poll_with_backoff(__test_fn, __backoff_fn);
70 }
71 
72 #else // _LIBCPP_HAS_NO_THREADS
73 
74 template <class _Tp>
75 _LIBCPP_HIDE_FROM_ABI void __cxx_atomic_notify_all(__cxx_atomic_impl<_Tp> const volatile*) { }
76 template <class _Tp>
77 _LIBCPP_HIDE_FROM_ABI void __cxx_atomic_notify_one(__cxx_atomic_impl<_Tp> const volatile*) { }
78 template <class _Atp, class _Fn>
79 _LIBCPP_HIDE_FROM_ABI bool __cxx_atomic_wait(_Atp*, _Fn && __test_fn)
80 {
81     return std::__libcpp_thread_poll_with_backoff(__test_fn, __spinning_backoff_policy());
82 }
83 
84 #endif // _LIBCPP_HAS_NO_THREADS
85 
86 template <typename _Tp> _LIBCPP_HIDE_FROM_ABI
87 bool __cxx_nonatomic_compare_equal(_Tp const& __lhs, _Tp const& __rhs) {
88     return std::memcmp(std::addressof(__lhs), std::addressof(__rhs), sizeof(_Tp)) == 0;
89 }
90 
91 template <class _Atp, class _Tp>
92 struct __cxx_atomic_wait_test_fn_impl {
93     _Atp* __a;
94     _Tp __val;
95     memory_order __order;
96     _LIBCPP_HIDE_FROM_ABI bool operator()() const
97     {
98         return !std::__cxx_nonatomic_compare_equal(std::__cxx_atomic_load(__a, __order), __val);
99     }
100 };
101 
102 template <class _Atp, class _Tp>
103 _LIBCPP_AVAILABILITY_SYNC
104 _LIBCPP_HIDE_FROM_ABI bool __cxx_atomic_wait(_Atp* __a, _Tp const __val, memory_order __order)
105 {
106     __cxx_atomic_wait_test_fn_impl<_Atp, _Tp> __test_fn = {__a, __val, __order};
107     return std::__cxx_atomic_wait(__a, __test_fn);
108 }
109 
110 _LIBCPP_END_NAMESPACE_STD
111 
112 #endif // _LIBCPP___ATOMIC_ATOMIC_SYNC_H
113