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// Support for atomic operations -*- C++ -*-
// Copyright (C) 2004-2021 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 ext/atomicity.h
* This file is a GNU extension to the Standard C++ Library.
*/
#ifndef _GLIBCXX_ATOMICITY_H
#define _GLIBCXX_ATOMICITY_H 1
#pragma GCC system_header
#include <bits/c++config.h>
#include <bits/gthr.h>
#include <bits/atomic_word.h>
#if __has_include(<sys/single_threaded.h>)
# include <sys/single_threaded.h>
#endif
namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
__attribute__((__always_inline__))
inline bool
__is_single_threaded() _GLIBCXX_NOTHROW
{
#ifndef __GTHREADS
return true;
#elif __has_include(<sys/single_threaded.h>)
return ::__libc_single_threaded;
#else
return !__gthread_active_p();
#endif
}
// Functions for portable atomic access.
// To abstract locking primitives across all thread policies, use:
// __exchange_and_add_dispatch
// __atomic_add_dispatch
#ifdef _GLIBCXX_ATOMIC_BUILTINS
inline _Atomic_word
__attribute__((__always_inline__))
__exchange_and_add(volatile _Atomic_word* __mem, int __val)
{ return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
inline void
__attribute__((__always_inline__))
__atomic_add(volatile _Atomic_word* __mem, int __val)
{ __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
#else
_Atomic_word
__exchange_and_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
void
__atomic_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
#endif
inline _Atomic_word
__attribute__((__always_inline__))
__exchange_and_add_single(_Atomic_word* __mem, int __val)
{
_Atomic_word __result = *__mem;
*__mem += __val;
return __result;
}
inline void
__attribute__((__always_inline__))
__atomic_add_single(_Atomic_word* __mem, int __val)
{ *__mem += __val; }
inline _Atomic_word
__attribute__ ((__always_inline__))
__exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
{
if (__is_single_threaded())
return __exchange_and_add_single(__mem, __val);
else
return __exchange_and_add(__mem, __val);
}
inline void
__attribute__ ((__always_inline__))
__atomic_add_dispatch(_Atomic_word* __mem, int __val)
{
if (__is_single_threaded())
__atomic_add_single(__mem, __val);
else
__atomic_add(__mem, __val);
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
// Even if the CPU doesn't need a memory barrier, we need to ensure
// that the compiler doesn't reorder memory accesses across the
// barriers.
#ifndef _GLIBCXX_READ_MEM_BARRIER
#define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
#endif
#ifndef _GLIBCXX_WRITE_MEM_BARRIER
#define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
#endif
#endif
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