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The C and C++ Include Header Files

/usr/include/c++/11/ext/atomicity.h


$ cat -n /usr/include/c++/11/ext/atomicity.h

     1	// Support for atomic operations -*- C++ -*-
     2	
     3	// Copyright (C) 2004-2021 Free Software Foundation, Inc.
     4	//
     5	// This file is part of the GNU ISO C++ Library.  This library is free
     6	// software; you can redistribute it and/or modify it under the
     7	// terms of the GNU General Public License as published by the
     8	// Free Software Foundation; either version 3, or (at your option)
     9	// any later version.
    10	
    11	// This library is distributed in the hope that it will be useful,
    12	// but WITHOUT ANY WARRANTY; without even the implied warranty of
    13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    14	// GNU General Public License for more details.
    15	
    16	// Under Section 7 of GPL version 3, you are granted additional
    17	// permissions described in the GCC Runtime Library Exception, version
    18	// 3.1, as published by the Free Software Foundation.
    19	
    20	// You should have received a copy of the GNU General Public License and
    21	// a copy of the GCC Runtime Library Exception along with this program;
    22	// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    23	// <http://www.gnu.org/licenses/>.
    24	
    25	/** @file ext/atomicity.h
    26	 *  This file is a GNU extension to the Standard C++ Library.
    27	 */
    28	
    29	#ifndef _GLIBCXX_ATOMICITY_H
    30	#define _GLIBCXX_ATOMICITY_H	1
    31	
    32	#pragma GCC system_header
    33	
    34	#include <bits/c++config.h>
    35	#include <bits/gthr.h>
    36	#include <bits/atomic_word.h>
    37	#if __has_include(<sys/single_threaded.h>)
    38	# include <sys/single_threaded.h>
    39	#endif
    40	
    41	namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
    42	{
    43	_GLIBCXX_BEGIN_NAMESPACE_VERSION
    44	
    45	  __attribute__((__always_inline__))
    46	  inline bool
    47	  __is_single_threaded() _GLIBCXX_NOTHROW
    48	  {
    49	#ifndef __GTHREADS
    50	    return true;
    51	#elif __has_include(<sys/single_threaded.h>)
    52	    return ::__libc_single_threaded;
    53	#else
    54	    return !__gthread_active_p();
    55	#endif
    56	  }
    57	
    58	  // Functions for portable atomic access.
    59	  // To abstract locking primitives across all thread policies, use:
    60	  // __exchange_and_add_dispatch
    61	  // __atomic_add_dispatch
    62	#ifdef _GLIBCXX_ATOMIC_BUILTINS
    63	  inline _Atomic_word
    64	  __attribute__((__always_inline__))
    65	  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
    66	  { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
    67	
    68	  inline void
    69	  __attribute__((__always_inline__))
    70	  __atomic_add(volatile _Atomic_word* __mem, int __val)
    71	  { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
    72	#else
    73	  _Atomic_word
    74	  __exchange_and_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
    75	
    76	  void
    77	  __atomic_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
    78	#endif
    79	
    80	  inline _Atomic_word
    81	  __attribute__((__always_inline__))
    82	  __exchange_and_add_single(_Atomic_word* __mem, int __val)
    83	  {
    84	    _Atomic_word __result = *__mem;
    85	    *__mem += __val;
    86	    return __result;
    87	  }
    88	
    89	  inline void
    90	  __attribute__((__always_inline__))
    91	  __atomic_add_single(_Atomic_word* __mem, int __val)
    92	  { *__mem += __val; }
    93	
    94	  inline _Atomic_word
    95	  __attribute__ ((__always_inline__))
    96	  __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
    97	  {
    98	    if (__is_single_threaded())
    99	      return __exchange_and_add_single(__mem, __val);
   100	    else
   101	      return __exchange_and_add(__mem, __val);
   102	  }
   103	
   104	  inline void
   105	  __attribute__ ((__always_inline__))
   106	  __atomic_add_dispatch(_Atomic_word* __mem, int __val)
   107	  {
   108	    if (__is_single_threaded())
   109	      __atomic_add_single(__mem, __val);
   110	    else
   111	      __atomic_add(__mem, __val);
   112	  }
   113	
   114	_GLIBCXX_END_NAMESPACE_VERSION
   115	} // namespace
   116	
   117	// Even if the CPU doesn't need a memory barrier, we need to ensure
   118	// that the compiler doesn't reorder memory accesses across the
   119	// barriers.
   120	#ifndef _GLIBCXX_READ_MEM_BARRIER
   121	#define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
   122	#endif
   123	#ifndef _GLIBCXX_WRITE_MEM_BARRIER
   124	#define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
   125	#endif
   126	
   127	#endif