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.
