xref: /freebsd/contrib/llvm-project/libcxx/include/latch (revision e8d8bef961a50d4dc22501cde4fb9fb0be1b2532)
15ffd83dbSDimitry Andric// -*- C++ -*-
25ffd83dbSDimitry Andric//===--------------------------- latch -----------------------------------===//
35ffd83dbSDimitry Andric//
45ffd83dbSDimitry Andric// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
55ffd83dbSDimitry Andric// See https://llvm.org/LICENSE.txt for license information.
65ffd83dbSDimitry Andric// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
75ffd83dbSDimitry Andric//
85ffd83dbSDimitry Andric//===----------------------------------------------------------------------===//
95ffd83dbSDimitry Andric
105ffd83dbSDimitry Andric#ifndef _LIBCPP_LATCH
115ffd83dbSDimitry Andric#define _LIBCPP_LATCH
125ffd83dbSDimitry Andric
135ffd83dbSDimitry Andric/*
145ffd83dbSDimitry Andric    latch synopsis
155ffd83dbSDimitry Andric
165ffd83dbSDimitry Andricnamespace std
175ffd83dbSDimitry Andric{
185ffd83dbSDimitry Andric
195ffd83dbSDimitry Andric  class latch
205ffd83dbSDimitry Andric  {
215ffd83dbSDimitry Andric  public:
22*e8d8bef9SDimitry Andric    static constexpr ptrdiff_t max() noexcept;
23*e8d8bef9SDimitry Andric
245ffd83dbSDimitry Andric    constexpr explicit latch(ptrdiff_t __expected);
255ffd83dbSDimitry Andric    ~latch();
265ffd83dbSDimitry Andric
275ffd83dbSDimitry Andric    latch(const latch&) = delete;
285ffd83dbSDimitry Andric    latch& operator=(const latch&) = delete;
295ffd83dbSDimitry Andric
305ffd83dbSDimitry Andric    void count_down(ptrdiff_t __update = 1);
315ffd83dbSDimitry Andric    bool try_wait() const noexcept;
325ffd83dbSDimitry Andric    void wait() const;
335ffd83dbSDimitry Andric    void arrive_and_wait(ptrdiff_t __update = 1);
345ffd83dbSDimitry Andric
355ffd83dbSDimitry Andric  private:
365ffd83dbSDimitry Andric    ptrdiff_t __counter; // exposition only
375ffd83dbSDimitry Andric  };
385ffd83dbSDimitry Andric
395ffd83dbSDimitry Andric}
405ffd83dbSDimitry Andric
415ffd83dbSDimitry Andric*/
425ffd83dbSDimitry Andric
435ffd83dbSDimitry Andric#include <__config>
44*e8d8bef9SDimitry Andric#include <__availability>
455ffd83dbSDimitry Andric#include <atomic>
465ffd83dbSDimitry Andric
475ffd83dbSDimitry Andric#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
485ffd83dbSDimitry Andric#pragma GCC system_header
495ffd83dbSDimitry Andric#endif
505ffd83dbSDimitry Andric
515ffd83dbSDimitry Andric#ifdef _LIBCPP_HAS_NO_THREADS
525ffd83dbSDimitry Andric# error <latch> is not supported on this single threaded system
535ffd83dbSDimitry Andric#endif
545ffd83dbSDimitry Andric
55*e8d8bef9SDimitry Andric_LIBCPP_PUSH_MACROS
56*e8d8bef9SDimitry Andric#include <__undef_macros>
57*e8d8bef9SDimitry Andric
585ffd83dbSDimitry Andric#if _LIBCPP_STD_VER >= 14
595ffd83dbSDimitry Andric
605ffd83dbSDimitry Andric_LIBCPP_BEGIN_NAMESPACE_STD
615ffd83dbSDimitry Andric
625ffd83dbSDimitry Andricclass latch
635ffd83dbSDimitry Andric{
645ffd83dbSDimitry Andric    __atomic_base<ptrdiff_t> __a;
655ffd83dbSDimitry Andric
665ffd83dbSDimitry Andricpublic:
675ffd83dbSDimitry Andric    static constexpr ptrdiff_t max() noexcept {
685ffd83dbSDimitry Andric        return numeric_limits<ptrdiff_t>::max();
695ffd83dbSDimitry Andric    }
705ffd83dbSDimitry Andric
715ffd83dbSDimitry Andric    inline _LIBCPP_INLINE_VISIBILITY
725ffd83dbSDimitry Andric    constexpr explicit latch(ptrdiff_t __expected) : __a(__expected) { }
735ffd83dbSDimitry Andric
745ffd83dbSDimitry Andric    ~latch() = default;
755ffd83dbSDimitry Andric    latch(const latch&) = delete;
765ffd83dbSDimitry Andric    latch& operator=(const latch&) = delete;
775ffd83dbSDimitry Andric
785ffd83dbSDimitry Andric    inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
795ffd83dbSDimitry Andric    void count_down(ptrdiff_t __update = 1)
805ffd83dbSDimitry Andric    {
815ffd83dbSDimitry Andric        auto const __old = __a.fetch_sub(__update, memory_order_release);
825ffd83dbSDimitry Andric        if(__old == __update)
835ffd83dbSDimitry Andric            __a.notify_all();
845ffd83dbSDimitry Andric    }
855ffd83dbSDimitry Andric    inline _LIBCPP_INLINE_VISIBILITY
865ffd83dbSDimitry Andric    bool try_wait() const noexcept
875ffd83dbSDimitry Andric    {
885ffd83dbSDimitry Andric        return 0 == __a.load(memory_order_acquire);
895ffd83dbSDimitry Andric    }
905ffd83dbSDimitry Andric    inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
915ffd83dbSDimitry Andric    void wait() const
925ffd83dbSDimitry Andric    {
935ffd83dbSDimitry Andric        auto const __test_fn = [=]() -> bool {
945ffd83dbSDimitry Andric            return try_wait();
955ffd83dbSDimitry Andric        };
965ffd83dbSDimitry Andric        __cxx_atomic_wait(&__a.__a_, __test_fn);
975ffd83dbSDimitry Andric    }
985ffd83dbSDimitry Andric    inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
995ffd83dbSDimitry Andric    void arrive_and_wait(ptrdiff_t __update = 1)
1005ffd83dbSDimitry Andric    {
1015ffd83dbSDimitry Andric        count_down(__update);
1025ffd83dbSDimitry Andric        wait();
1035ffd83dbSDimitry Andric    }
1045ffd83dbSDimitry Andric};
1055ffd83dbSDimitry Andric
1065ffd83dbSDimitry Andric_LIBCPP_END_NAMESPACE_STD
1075ffd83dbSDimitry Andric
1085ffd83dbSDimitry Andric#endif // _LIBCPP_STD_VER >= 14
1095ffd83dbSDimitry Andric
110*e8d8bef9SDimitry Andric_LIBCPP_POP_MACROS
111*e8d8bef9SDimitry Andric
1125ffd83dbSDimitry Andric#endif //_LIBCPP_LATCH
113