forked from OSchip/llvm-project
241 lines
6.6 KiB
C++
241 lines
6.6 KiB
C++
// -*- C++ -*-
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//===--------------------------- semaphore --------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP_SEMAPHORE
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#define _LIBCPP_SEMAPHORE
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/*
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semaphore synopsis
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namespace std {
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template<ptrdiff_t least_max_value = implementation-defined>
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class counting_semaphore
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{
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public:
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static constexpr ptrdiff_t max() noexcept;
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constexpr explicit counting_semaphore(ptrdiff_t desired);
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~counting_semaphore();
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counting_semaphore(const counting_semaphore&) = delete;
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counting_semaphore& operator=(const counting_semaphore&) = delete;
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void release(ptrdiff_t update = 1);
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void acquire();
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bool try_acquire() noexcept;
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template<class Rep, class Period>
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bool try_acquire_for(const chrono::duration<Rep, Period>& rel_time);
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template<class Clock, class Duration>
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bool try_acquire_until(const chrono::time_point<Clock, Duration>& abs_time);
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private:
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ptrdiff_t counter; // exposition only
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};
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using binary_semaphore = counting_semaphore<1>;
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}
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*/
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#include <__config>
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#include <__availability>
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#include <__threading_support>
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#include <atomic>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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#pragma GCC system_header
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#endif
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#ifdef _LIBCPP_HAS_NO_THREADS
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# error <semaphore> is not supported on this single threaded system
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#endif
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_LIBCPP_PUSH_MACROS
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#include <__undef_macros>
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#if _LIBCPP_STD_VER >= 14
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_LIBCPP_BEGIN_NAMESPACE_STD
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/*
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__atomic_semaphore_base is the general-case implementation, to be used for
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user-requested least-max values that exceed the OS implementation support
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(incl. when the OS has no support of its own) and for binary semaphores.
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It is a typical Dijsktra semaphore algorithm over atomics, wait and notify
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functions. It avoids contention against users' own use of those facilities.
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*/
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class __atomic_semaphore_base
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{
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__atomic_base<ptrdiff_t> __a;
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public:
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_LIBCPP_INLINE_VISIBILITY
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__atomic_semaphore_base(ptrdiff_t __count) : __a(__count)
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{
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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void release(ptrdiff_t __update = 1)
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{
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if(0 < __a.fetch_add(__update, memory_order_release))
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;
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else if(__update > 1)
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__a.notify_all();
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else
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__a.notify_one();
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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void acquire()
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{
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auto const __test_fn = [=]() -> bool {
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auto __old = __a.load(memory_order_relaxed);
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return (__old != 0) && __a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed);
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};
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__cxx_atomic_wait(&__a.__a_, __test_fn);
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}
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template <class Rep, class Period>
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
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{
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auto const __test_fn = [=]() -> bool {
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auto __old = __a.load(memory_order_acquire);
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while(1) {
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if (__old == 0)
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return false;
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if(__a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed))
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return true;
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}
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};
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return __libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy(), __rel_time);
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}
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};
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#ifndef _LIBCPP_NO_NATIVE_SEMAPHORES
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/*
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__platform_semaphore_base a simple wrapper for the OS semaphore type. That
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is, every call is routed to the OS in the most direct manner possible.
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*/
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class __platform_semaphore_base
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{
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__libcpp_semaphore_t __semaphore;
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public:
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_LIBCPP_INLINE_VISIBILITY
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__platform_semaphore_base(ptrdiff_t __count) :
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__semaphore()
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{
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__libcpp_semaphore_init(&__semaphore, __count);
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}
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_LIBCPP_INLINE_VISIBILITY
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~__platform_semaphore_base() {
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__libcpp_semaphore_destroy(&__semaphore);
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}
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_LIBCPP_INLINE_VISIBILITY
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void release(ptrdiff_t __update)
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{
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for(; __update; --__update)
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__libcpp_semaphore_post(&__semaphore);
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}
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_LIBCPP_INLINE_VISIBILITY
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void acquire()
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{
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__libcpp_semaphore_wait(&__semaphore);
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}
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_LIBCPP_INLINE_VISIBILITY
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bool try_acquire_for(chrono::nanoseconds __rel_time)
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{
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return __libcpp_semaphore_wait_timed(&__semaphore, __rel_time);
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}
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};
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template<ptrdiff_t __least_max_value>
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using __semaphore_base =
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typename conditional<(__least_max_value > 1 && __least_max_value <= _LIBCPP_SEMAPHORE_MAX),
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__platform_semaphore_base,
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__atomic_semaphore_base>::type;
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#else
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template<ptrdiff_t __least_max_value>
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using __semaphore_base =
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__atomic_semaphore_base;
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#define _LIBCPP_SEMAPHORE_MAX (numeric_limits<ptrdiff_t>::max())
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#endif //_LIBCPP_NO_NATIVE_SEMAPHORES
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template<ptrdiff_t __least_max_value = _LIBCPP_SEMAPHORE_MAX>
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class counting_semaphore
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{
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__semaphore_base<__least_max_value> __semaphore;
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public:
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static constexpr ptrdiff_t max() noexcept {
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return __least_max_value;
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}
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_LIBCPP_INLINE_VISIBILITY
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counting_semaphore(ptrdiff_t __count = 0) : __semaphore(__count) { }
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~counting_semaphore() = default;
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counting_semaphore(const counting_semaphore&) = delete;
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counting_semaphore& operator=(const counting_semaphore&) = delete;
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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void release(ptrdiff_t __update = 1)
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{
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__semaphore.release(__update);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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void acquire()
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{
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__semaphore.acquire();
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}
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template<class Rep, class Period>
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
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{
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return __semaphore.try_acquire_for(chrono::duration_cast<chrono::nanoseconds>(__rel_time));
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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bool try_acquire()
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{
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return try_acquire_for(chrono::nanoseconds::zero());
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}
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template <class Clock, class Duration>
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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bool try_acquire_until(chrono::time_point<Clock, Duration> const& __abs_time)
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{
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auto const current = Clock::now();
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if(current >= __abs_time)
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return try_acquire();
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else
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return try_acquire_for(__abs_time - current);
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}
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};
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using binary_semaphore = counting_semaphore<1>;
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP_STD_VER >= 14
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_LIBCPP_POP_MACROS
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#endif //_LIBCPP_SEMAPHORE
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