Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/semaphore

@@ -0,0 +1,198 @@
+// -*- 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_SEMAPHORE
+#define _LIBCPP_SEMAPHORE
+
+/*
+    semaphore synopsis
+
+namespace std {
+
+template<ptrdiff_t least_max_value = implementation-defined>
+class counting_semaphore
+{
+public:
+static constexpr ptrdiff_t max() noexcept;
+
+constexpr explicit counting_semaphore(ptrdiff_t desired);
+~counting_semaphore();
+
+counting_semaphore(const counting_semaphore&) = delete;
+counting_semaphore& operator=(const counting_semaphore&) = delete;
+
+void release(ptrdiff_t update = 1);
+void acquire();
+bool try_acquire() noexcept;
+template<class Rep, class Period>
+    bool try_acquire_for(const chrono::duration<Rep, Period>& rel_time);
+template<class Clock, class Duration>
+    bool try_acquire_until(const chrono::time_point<Clock, Duration>& abs_time);
+
+private:
+ptrdiff_t counter; // exposition only
+};
+
+using binary_semaphore = counting_semaphore<1>;
+
+}
+
+*/
+
+#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 <__chrono/time_point.h>
+#include <__config>
+#include <__thread/timed_backoff_policy.h>
+#include <__threading_support>
+#include <cstddef>
+#include <limits>
+#include <version>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#ifdef _LIBCPP_HAS_NO_THREADS
+# error "<semaphore> is not supported since libc++ has been configured without support for threads."
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+#if _LIBCPP_STD_VER >= 14
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+/*
+
+__atomic_semaphore_base is the general-case implementation.
+It is a typical Dijkstra semaphore algorithm over atomics, wait and notify
+functions. It avoids contention against users' own use of those facilities.
+
+*/
+
+class __atomic_semaphore_base
+{
+    __atomic_base<ptrdiff_t> __a_;
+
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit __atomic_semaphore_base(ptrdiff_t __count) : __a_(__count)
+    {
+    }
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    void release(ptrdiff_t __update = 1)
+    {
+        if(0 < __a_.fetch_add(__update, memory_order_release))
+            ;
+        else if(__update > 1)
+            __a_.notify_all();
+        else
+            __a_.notify_one();
+    }
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    void acquire()
+    {
+        auto const __test_fn = [this]() -> bool {
+            auto __old = __a_.load(memory_order_relaxed);
+            return (__old != 0) && __a_.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed);
+        };
+        __cxx_atomic_wait(&__a_.__a_, __test_fn);
+    }
+    template <class Rep, class Period>
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
+    {
+        if (__rel_time == chrono::duration<Rep, Period>::zero())
+            return try_acquire();
+        auto const __test_fn = [this]() { return try_acquire(); };
+        return std::__libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy(), __rel_time);
+    }
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    bool try_acquire()
+    {
+        auto __old = __a_.load(memory_order_acquire);
+        while (true) {
+            if (__old == 0)
+                return false;
+            if (__a_.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed))
+                return true;
+        }
+    }
+};
+
+#define _LIBCPP_SEMAPHORE_MAX (numeric_limits<ptrdiff_t>::max())
+
+template<ptrdiff_t __least_max_value = _LIBCPP_SEMAPHORE_MAX>
+class counting_semaphore
+{
+    __atomic_semaphore_base __semaphore_;
+
+public:
+    static constexpr ptrdiff_t max() noexcept {
+        return __least_max_value;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit counting_semaphore(ptrdiff_t __count) : __semaphore_(__count) { }
+    ~counting_semaphore() = default;
+
+    counting_semaphore(const counting_semaphore&) = delete;
+    counting_semaphore& operator=(const counting_semaphore&) = delete;
+
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    void release(ptrdiff_t __update = 1)
+    {
+        __semaphore_.release(__update);
+    }
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    void acquire()
+    {
+        __semaphore_.acquire();
+    }
+    template<class Rep, class Period>
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time)
+    {
+        return __semaphore_.try_acquire_for(chrono::duration_cast<chrono::nanoseconds>(__rel_time));
+    }
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    bool try_acquire()
+    {
+        return __semaphore_.try_acquire();
+    }
+    template <class Clock, class Duration>
+    _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    bool try_acquire_until(chrono::time_point<Clock, Duration> const& __abs_time)
+    {
+        auto const __current = Clock::now();
+        if (__current >= __abs_time)
+            return try_acquire();
+        else
+            return try_acquire_for(__abs_time - __current);
+    }
+};
+
+using binary_semaphore = counting_semaphore<1>;
+
+_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_SEMAPHORE