xref: /freebsd/contrib/llvm-project/libcxx/include/latch (revision 7a6dacaca14b62ca4b74406814becb87a3fefac0)

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_LATCH
#define _LIBCPP_LATCH

/*
    latch synopsis

namespace std
{

  class latch
  {
  public:
    static constexpr ptrdiff_t max() noexcept;

    constexpr explicit latch(ptrdiff_t __expected);
    ~latch();

    latch(const latch&) = delete;
    latch& operator=(const latch&) = delete;

    void count_down(ptrdiff_t __update = 1);
    bool try_wait() const noexcept;
    void wait() const;
    void arrive_and_wait(ptrdiff_t __update = 1);

  private:
    ptrdiff_t __counter; // exposition only
  };

}

*/

#include <__config>

#ifdef _LIBCPP_HAS_NO_THREADS
#  error "<latch> is not supported since libc++ has been configured without support for threads."
#endif

#include <__assert> // all public C++ headers provide the assertion handler
#include <__atomic/atomic_base.h>
#include <__atomic/atomic_sync.h>
#include <__atomic/memory_order.h>
#include <__availability>
#include <cstddef>
#include <limits>
#include <version>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

#if _LIBCPP_STD_VER >= 14

_LIBCPP_BEGIN_NAMESPACE_STD

class latch {
  __atomic_base<ptrdiff_t> __a_;

public:
  static _LIBCPP_HIDE_FROM_ABI constexpr ptrdiff_t max() noexcept { return numeric_limits<ptrdiff_t>::max(); }

  inline _LIBCPP_HIDE_FROM_ABI constexpr explicit latch(ptrdiff_t __expected) : __a_(__expected) {
    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
        __expected >= 0,
        "latch::latch(ptrdiff_t): latch cannot be "
        "initialized with a negative value");
    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
        __expected <= max(),
        "latch::latch(ptrdiff_t): latch cannot be "
        "initialized with a value greater than max()");
  }

  _LIBCPP_HIDE_FROM_ABI ~latch() = default;
  latch(const latch&)            = delete;
  latch& operator=(const latch&) = delete;

  inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void count_down(ptrdiff_t __update = 1) {
    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__update >= 0, "latch::count_down called with a negative value");
    auto const __old = __a_.fetch_sub(__update, memory_order_release);
    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
        __update <= __old,
        "latch::count_down called with a value greater "
        "than the internal counter");
    if (__old == __update)
      __a_.notify_all();
  }
  inline _LIBCPP_HIDE_FROM_ABI bool try_wait() const noexcept { return 0 == __a_.load(memory_order_acquire); }
  inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait() const {
    __cxx_atomic_wait(&__a_.__a_, [this]() -> bool { return try_wait(); });
  }
  inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void arrive_and_wait(ptrdiff_t __update = 1) {
    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__update >= 0, "latch::arrive_and_wait called with a negative value");
    // other preconditions on __update are checked in count_down()

    count_down(__update);
    wait();
  }
};

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_STD_VER >= 14

_LIBCPP_POP_MACROS

#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
#  include <atomic>
#endif

#endif //_LIBCPP_LATCH