xref: /freebsd/contrib/llvm-project/libcxx/include/latch (revision 1db9f3b21e39176dd5b67cf8ac378633b172463e)
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
16namespace 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
68class latch {
69  __atomic_base<ptrdiff_t> __a_;
70
71public:
72  static _LIBCPP_HIDE_FROM_ABI constexpr ptrdiff_t max() noexcept { return numeric_limits<ptrdiff_t>::max(); }
73
74  inline _LIBCPP_HIDE_FROM_ABI constexpr explicit latch(ptrdiff_t __expected) : __a_(__expected) {
75    _LIBCPP_ASSERT_UNCATEGORIZED(
76        __expected >= 0,
77        "latch::latch(ptrdiff_t): latch cannot be "
78        "initialized with a negative value");
79    _LIBCPP_ASSERT_UNCATEGORIZED(
80        __expected <= max(),
81        "latch::latch(ptrdiff_t): latch cannot be "
82        "initialized with a value greater than max()");
83  }
84
85  _LIBCPP_HIDE_FROM_ABI ~latch() = default;
86  latch(const latch&)            = delete;
87  latch& operator=(const latch&) = delete;
88
89  inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void count_down(ptrdiff_t __update = 1) {
90    _LIBCPP_ASSERT_UNCATEGORIZED(__update >= 0, "latch::count_down called with a negative value");
91    auto const __old = __a_.fetch_sub(__update, memory_order_release);
92    _LIBCPP_ASSERT_UNCATEGORIZED(
93        __update <= __old,
94        "latch::count_down called with a value greater "
95        "than the internal counter");
96    if (__old == __update)
97      __a_.notify_all();
98  }
99  inline _LIBCPP_HIDE_FROM_ABI bool try_wait() const noexcept { return 0 == __a_.load(memory_order_acquire); }
100  inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait() const {
101    __cxx_atomic_wait(&__a_.__a_, [this]() -> bool { return try_wait(); });
102  }
103  inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void arrive_and_wait(ptrdiff_t __update = 1) {
104    _LIBCPP_ASSERT_UNCATEGORIZED(__update >= 0, "latch::arrive_and_wait called with a negative value");
105    // other preconditions on __update are checked in count_down()
106
107    count_down(__update);
108    wait();
109  }
110};
111
112_LIBCPP_END_NAMESPACE_STD
113
114#endif // _LIBCPP_STD_VER >= 14
115
116_LIBCPP_POP_MACROS
117
118#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
119#  include <atomic>
120#endif
121
122#endif //_LIBCPP_LATCH
123