contrib/llvm-project/libcxx/include/semaphore

   1 // -*- C++ -*-
   2 //===--------------------------- semaphore --------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP_SEMAPHORE
  11 #define _LIBCPP_SEMAPHORE
  12
  13 /*
  14     semaphore synopsis
  15
  16 namespace std {
  17
  18 template<ptrdiff_t least_max_value = implementation-defined>
  19 class counting_semaphore
  20 {
  21 public:
  22 static constexpr ptrdiff_t max() noexcept;
  23
  24 constexpr explicit counting_semaphore(ptrdiff_t desired);
  25 ~counting_semaphore();
  26
  27 counting_semaphore(const counting_semaphore&) = delete;
  28 counting_semaphore& operator=(const counting_semaphore&) = delete;
  29
  30 void release(ptrdiff_t update = 1);
  31 void acquire();
  32 bool try_acquire() noexcept;
  33 template<class Rep, class Period>
  34     bool try_acquire_for(const chrono::duration<Rep, Period>& rel_time);
  35 template<class Clock, class Duration>
  36     bool try_acquire_until(const chrono::time_point<Clock, Duration>& abs_time);
  37
  38 private:
  39 ptrdiff_t counter; // exposition only
  40 };
  41
  42 using binary_semaphore = counting_semaphore<1>;
  43
  44 }
  45
  46 */
  47
  48 #include <__availability>
  49 #include <__config>
  50 #include <__threading_support>
  51 #include <atomic>
  52
  53 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  54 #pragma GCC system_header
  55 #endif
  56
  57 #ifdef _LIBCPP_HAS_NO_THREADS
  58 # error <semaphore> is not supported on this single threaded system
  59 #endif
  60
  61 _LIBCPP_PUSH_MACROS
  62 #include <__undef_macros>
  63
  64 #if _LIBCPP_STD_VER >= 14
  65
  66 _LIBCPP_BEGIN_NAMESPACE_STD
  67
  68 /*
  69
  70 __atomic_semaphore_base is the general-case implementation, to be used for
  71 user-requested least-max values that exceed the OS implementation support
  72 (incl. when the OS has no support of its own) and for binary semaphores.
  73
  74 It is a typical Dijkstra semaphore algorithm over atomics, wait and notify
  75 functions. It avoids contention against users' own use of those facilities.
  76
  77 */
  78
  79 class __atomic_semaphore_base
  80 {
  81     __atomic_base<ptrdiff_t> __a;
  82
  83 public:
  84     _LIBCPP_INLINE_VISIBILITY
  85     __atomic_semaphore_base(ptrdiff_t __count) : __a(__count)
  86     {
  87     }
  88     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
  89     void release(ptrdiff_t __update = 1)
  90     {
  91         if(0 < __a.fetch_add(__update, memory_order_release))
  92             ;
  93         else if(__update > 1)
  94             __a.notify_all();
  95         else
  96             __a.notify_one();
  97     }
  98     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
  99     void acquire()
 100     {
 101         auto const __test_fn = [this]() -> bool {
 102             auto __old = __a.load(memory_order_relaxed);
 103             return (__old != 0) && __a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed);
 104         };
 105         __cxx_atomic_wait(&__a.__a_, __test_fn);
 106     }
 107     template <class Rep, class Period>
 108     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 109     bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
 110     {
 111         auto const __test_fn = [this]() -> bool {
 112             auto __old = __a.load(memory_order_acquire);
 113             while(1) {
 114                 if (__old == 0)
 115                     return false;
 116                 if(__a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed))
 117                     return true;
 118             }
 119         };
 120         return __libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy(), __rel_time);
 121     }
 122 };
 123
 124 #ifndef _LIBCPP_NO_NATIVE_SEMAPHORES
 125
 126 /*
 127
 128 __platform_semaphore_base a simple wrapper for the OS semaphore type. That
 129 is, every call is routed to the OS in the most direct manner possible.
 130
 131 */
 132
 133 class __platform_semaphore_base
 134 {
 135     __libcpp_semaphore_t __semaphore;
 136
 137 public:
 138     _LIBCPP_INLINE_VISIBILITY
 139     __platform_semaphore_base(ptrdiff_t __count) :
 140         __semaphore()
 141     {
 142         __libcpp_semaphore_init(&__semaphore, __count);
 143     }
 144     _LIBCPP_INLINE_VISIBILITY
 145     ~__platform_semaphore_base() {
 146         __libcpp_semaphore_destroy(&__semaphore);
 147     }
 148     _LIBCPP_INLINE_VISIBILITY
 149     void release(ptrdiff_t __update)
 150     {
 151         for(; __update; --__update)
 152             __libcpp_semaphore_post(&__semaphore);
 153     }
 154     _LIBCPP_INLINE_VISIBILITY
 155     void acquire()
 156     {
 157         __libcpp_semaphore_wait(&__semaphore);
 158     }
 159     _LIBCPP_INLINE_VISIBILITY
 160     bool try_acquire_for(chrono::nanoseconds __rel_time)
 161     {
 162         return __libcpp_semaphore_wait_timed(&__semaphore, __rel_time);
 163     }
 164 };
 165
 166 template<ptrdiff_t __least_max_value>
 167 using __semaphore_base =
 168     typename conditional<(__least_max_value > 1 && __least_max_value <= _LIBCPP_SEMAPHORE_MAX),
 169                          __platform_semaphore_base,
 170                          __atomic_semaphore_base>::type;
 171
 172 #else
 173
 174 template<ptrdiff_t __least_max_value>
 175 using __semaphore_base =
 176     __atomic_semaphore_base;
 177
 178 #define _LIBCPP_SEMAPHORE_MAX (numeric_limits<ptrdiff_t>::max())
 179
 180 #endif //_LIBCPP_NO_NATIVE_SEMAPHORES
 181
 182 template<ptrdiff_t __least_max_value = _LIBCPP_SEMAPHORE_MAX>
 183 class counting_semaphore
 184 {
 185     __semaphore_base<__least_max_value> __semaphore;
 186
 187 public:
 188     static constexpr ptrdiff_t max() noexcept {
 189         return __least_max_value;
 190     }
 191
 192     _LIBCPP_INLINE_VISIBILITY
 193     counting_semaphore(ptrdiff_t __count = 0) : __semaphore(__count) { }
 194     ~counting_semaphore() = default;
 195
 196     counting_semaphore(const counting_semaphore&) = delete;
 197     counting_semaphore& operator=(const counting_semaphore&) = delete;
 198
 199     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 200     void release(ptrdiff_t __update = 1)
 201     {
 202         __semaphore.release(__update);
 203     }
 204     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 205     void acquire()
 206     {
 207         __semaphore.acquire();
 208     }
 209     template<class Rep, class Period>
 210     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 211     bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
 212     {
 213         return __semaphore.try_acquire_for(chrono::duration_cast<chrono::nanoseconds>(__rel_time));
 214     }
 215     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 216     bool try_acquire()
 217     {
 218         return try_acquire_for(chrono::nanoseconds::zero());
 219     }
 220     template <class Clock, class Duration>
 221     _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 222     bool try_acquire_until(chrono::time_point<Clock, Duration> const& __abs_time)
 223     {
 224         auto const current = Clock::now();
 225         if(current >= __abs_time)
 226             return try_acquire();
 227         else
 228             return try_acquire_for(__abs_time - current);
 229     }
 230 };
 231
 232 using binary_semaphore = counting_semaphore<1>;
 233
 234 _LIBCPP_END_NAMESPACE_STD
 235
 236 #endif // _LIBCPP_STD_VER >= 14
 237
 238 _LIBCPP_POP_MACROS
 239
 240 #endif //_LIBCPP_SEMAPHORE