From: Jonathan Wakely <jwakely@redhat.com>
To: Thomas Rodgers <trodgers@redhat.com>
Cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org
Subject: Re: [PATCH] Add c++2a binary_semaphore
Date: Tue, 18 Feb 2020 14:25:00 -0000 [thread overview]
Message-ID: <20200218142541.GD9441@redhat.com> (raw)
In-Reply-To: <1291008602.5930779.1582008369882.JavaMail.zimbra@redhat.com>
On 18/02/20 01:46 -0500, Thomas Rodgers wrote:
>This patch adds the c++2a semaphore header and binary_semaphore type. The implementation is not complete, this patch is just to solicit initial feedback.
Here is some initial feedback on comments and whitespace :-)
>diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
>index 89835759069..2dbb7d3a6b1 100644
>--- a/libstdc++-v3/include/Makefile.am
>+++ b/libstdc++-v3/include/Makefile.am
>@@ -69,6 +69,7 @@ std_headers = \
> ${std_srcdir}/ratio \
> ${std_srcdir}/regex \
> ${std_srcdir}/scoped_allocator \
>+ ${std_srcdir}/semaphore \
Indentation is borked.
> ${std_srcdir}/set \
> ${std_srcdir}/shared_mutex \
> ${std_srcdir}/span \
>diff --git a/libstdc++-v3/include/std/semaphore b/libstdc++-v3/include/std/semaphore
>new file mode 100644
>index 00000000000..e3e88a50eec
>--- /dev/null
>+++ b/libstdc++-v3/include/std/semaphore
>@@ -0,0 +1,131 @@
>+// <stop_token> -*- C++ -*-
Wrong header name in comment.
>+
>+// Copyright (C) 2019-2020 Free Software Foundation, Inc.
>+//
>+// This file is part of the GNU ISO C++ Library. This library is free
>+// software; you can redistribute it and/or modify it under the
>+// terms of the GNU General Public License as published by the
>+// Free Software Foundation; either version 3, or (at your option)
>+// any later version.
>+
>+// This library is distributed in the hope that it will be useful,
>+// but WITHOUT ANY WARRANTY; without even the implied warranty of
>+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>+// GNU General Public License for more details.
>+
>+// Under Section 7 of GPL version 3, you are granted additional
>+// permissions described in the GCC Runtime Library Exception, version
>+// 3.1, as published by the Free Software Foundation.
>+
>+// You should have received a copy of the GNU General Public License and
>+// a copy of the GCC Runtime Library Exception along with this program;
>+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
>+// <http://www.gnu.org/licenses/>.
>+
>+/** @file include/stop_token
Wrong name again.
>+ * This is a Standard C++ Library header.
>+ */
>+
>+#ifndef _GLIBCXX_SEMAPHORE
>+#define _GLIBCXX_SEMAPHORE
>+
>+#if __cplusplus > 201703L
>+#define __cpp_lib_semaphore 201907L
We shouldn't define this until the file is complete, i.e. when it
provides binary_semaphore and counting_semaphore.
>+
>+#include <cstddef>
Is this header needed? ptrdiff_t and size_t are both defined in
<bits/c++config.h> which every header already includes.
>+#include <atomic>
>+#include <chrono>
>+
>+namespace std _GLIBCXX_VISIBILITY(default)
>+{
>+_GLIBCXX_BEGIN_NAMESPACE_VERSION
>+
>+ // TODO: replace this with a real implementation of std::binary_semaphore
>+ struct binary_semaphore
>+{
Indentation is borked here too.
>+ explicit binary_semaphore(int __d) : _M_counter(__d > 0) { }
>+
>+ static constexpr std::ptrdiff_t
>+ max() noexcept
>+ {
>+ return 1;
>+ }
>+
>+ void release() { _M_counter.fetch_add(1, memory_order::release); }
>+
>+ void acquire()
>+ {
>+ while (!_M_try_acquire())
>+ {
>+ _S_yield();
>+ }
>+ }
>+
>+ bool
>+ try_acquire() noexcept
>+ {
>+ return _M_try_acquire(1u);
>+ }
>+
>+ template<class _Rep, class _Period>
>+ bool try_acquire_for(const std::chrono::duration<_Rep, _Period>& __rel_time)
>+ {
>+ auto __abst = std::chrono::steady_clock::now() + __rel_time;
>+ return try_acquire_until(__abst);
>+ }
>+
>+ template<class _Clock, class _Duration>
>+ bool try_acquire_until(const std::chrono::time_point<_Clock, _Duration>& __abs_time)
>+ {
>+ do
>+ {
>+ if (_M_try_acquire())
>+ {
>+ return true;
>+ }
>+ } while (std::chrono::steady_clock::now() < __abs_time);
>+ return false;
>+ }
>+
>+private:
>+ static void
>+ _S_yield() noexcept
>+ {
>+#if defined __i386__ || defined __x86_64__
>+ __builtin_ia32_pause();
>+#elif defined _GLIBCXX_USE_SCHED_YIELD
>+ __gthread_yield();
>+#endif
>+ }
>+
>+ bool
>+ _M_try_acquire(unsigned __spin_ct)
>+ {
>+ int __old = 1;
>+ while (!_M_counter.compare_exchange_weak(__old, 0,
>+ memory_order::acquire,
>+ memory_order::relaxed))
>+ {
>+ if (--__spin_ct == 0)
>+ {
>+ return false;
>+ }
>+ __old = 1;
>+ }
>+ return true;
>+ }
>+
>+ static constexpr unsigned _S_spin_ct = 64u;
>+ bool
>+ _M_try_acquire()
>+ {
>+ return _M_try_acquire(1);
>+ }
>+
>+ atomic<int> _M_counter;
>+};
>+
>+_GLIBCXX_END_NAMESPACE_VERSION
>+} // namespace
>+#endif // __cplusplus > 201703L
>+#endif // _GLIBCXX_STOP_TOKEN
Wrong macro name in comment.
next prev parent reply other threads:[~2020-02-18 14:25 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <381004109.5930741.1582008200673.JavaMail.zimbra@redhat.com>
2020-02-18 6:46 ` Thomas Rodgers
2020-02-18 13:49 ` Sebastian Huber
2020-02-18 14:31 ` Jonathan Wakely
2020-02-21 12:33 ` Sebastian Huber
2020-02-18 14:25 ` Jonathan Wakely [this message]
2020-02-20 3:19 ` Thomas Rodgers
2020-02-25 2:53 ` Thomas Rodgers
2020-02-25 8:53 ` Sebastian Huber
2020-02-25 12:33 ` Jonathan Wakely
2020-02-25 12:39 ` Jonathan Wakely
2020-02-26 16:07 ` Jonathan Wakely
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