contrib/llvm-project/libcxx/include/latch

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   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_LATCH
  11 #define _LIBCPP_LATCH
  12
  13 /*
  14     latch synopsis
  15
  16 namespace std
  17 {
  18
  19   class latch
  20   {
  21   public:
  22     static constexpr ptrdiff_t max() noexcept;
  23
  24     constexpr explicit latch(ptrdiff_t __expected);
  25     ~latch();
  26
  27     latch(const latch&) = delete;
  28     latch& operator=(const latch&) = delete;
  29
  30     void count_down(ptrdiff_t __update = 1);
  31     bool try_wait() const noexcept;
  32     void wait() const;
  33     void arrive_and_wait(ptrdiff_t __update = 1);
  34
  35   private:
  36     ptrdiff_t __counter; // exposition only
  37   };
  38
  39 }
  40
  41 */
  42
  43 #include <__assert> // all public C++ headers provide the assertion handler
  44 #include <__atomic/atomic_base.h>
  45 #include <__atomic/atomic_sync.h>
  46 #include <__atomic/memory_order.h>
  47 #include <__availability>
  48 #include <__config>
  49 #include <cstddef>
  50 #include <limits>
  51 #include <version>
  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 "<latch> is not supported since libc++ has been configured without support for threads."
  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 class latch
  69 {
  70     __atomic_base<ptrdiff_t> __a_;
  71
  72 public:
  73     static _LIBCPP_HIDE_FROM_ABI constexpr ptrdiff_t max() noexcept {
  74         return numeric_limits<ptrdiff_t>::max();
  75     }
  76
  77     inline _LIBCPP_INLINE_VISIBILITY
  78     constexpr explicit latch(ptrdiff_t __expected) : __a_(__expected)
  79     {
  80         _LIBCPP_ASSERT_UNCATEGORIZED(__expected >= 0,
  81                                      "latch::latch(ptrdiff_t): latch cannot be "
  82                                      "initialized with a negative value");
  83         _LIBCPP_ASSERT_UNCATEGORIZED(__expected <= max(),
  84                                      "latch::latch(ptrdiff_t): latch cannot be "
  85                                      "initialized with a value greater than max()");
  86     }
  87
  88     _LIBCPP_HIDE_FROM_ABI ~latch() = default;
  89     latch(const latch&) = delete;
  90     latch& operator=(const latch&) = delete;
  91
  92     inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
  93     void count_down(ptrdiff_t __update = 1)
  94     {
  95         _LIBCPP_ASSERT_UNCATEGORIZED(
  96             __update >= 0, "latch::count_down called with a negative value");
  97         auto const __old = __a_.fetch_sub(__update, memory_order_release);
  98         _LIBCPP_ASSERT_UNCATEGORIZED(
  99             __update <= __old, "latch::count_down called with a value greater "
 100                                "than the internal counter");
 101         if (__old == __update)
 102             __a_.notify_all();
 103     }
 104     inline _LIBCPP_INLINE_VISIBILITY
 105     bool try_wait() const noexcept
 106     {
 107         return 0 == __a_.load(memory_order_acquire);
 108     }
 109     inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 110     void wait() const
 111     {
 112         __cxx_atomic_wait(&__a_.__a_, [this]() -> bool {
 113             return try_wait();
 114         });
 115     }
 116     inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
 117     void arrive_and_wait(ptrdiff_t __update = 1)
 118     {
 119         _LIBCPP_ASSERT_UNCATEGORIZED(
 120             __update >= 0, "latch::arrive_and_wait called with a negative value");
 121         // other preconditions on __update are checked in count_down()
 122
 123         count_down(__update);
 124         wait();
 125     }
 126 };
 127
 128 _LIBCPP_END_NAMESPACE_STD
 129
 130 #endif // _LIBCPP_STD_VER >= 14
 131
 132 _LIBCPP_POP_MACROS
 133
 134 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 135 #  include <atomic>
 136 #endif
 137
 138 #endif //_LIBCPP_LATCH