Where Online Learning is simpler!

The C and C++ Include Header Files

cat -n /usr/include/c++/15/ext/atomicity.h

     1	// Support for atomic operations -*- C++ -*-
     2	
     3	// Copyright (C) 2004-2025 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	#ifdef _GLIBCXX_SYSHDR
    33	#pragma GCC system_header
    34	#endif
    35	
    36	#include <bits/c++config.h>
    37	#include <bits/gthr.h>
    38	#include <bits/atomic_word.h>
    39	#if __has_include(<sys/single_threaded.h>)
    40	# include <sys/single_threaded.h>
    41	#endif
    42	
    43	namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
    44	{
    45	_GLIBCXX_BEGIN_NAMESPACE_VERSION
    46	
    47	  __attribute__((__always_inline__))
    48	  inline bool
    49	  __is_single_threaded() _GLIBCXX_NOTHROW
    50	  {
    51	#ifndef __GTHREADS
    52	    return true;
    53	#elif __has_include(<sys/single_threaded.h>)
    54	    return ::__libc_single_threaded;
    55	#else
    56	    return !__gthread_active_p();
    57	#endif
    58	  }
    59	
    60	  // Functions for portable atomic access.
    61	  // To abstract locking primitives across all thread policies, use:
    62	  // __exchange_and_add_dispatch
    63	  // __atomic_add_dispatch
    64	#ifdef _GLIBCXX_ATOMIC_BUILTINS
    65	  inline _Atomic_word
    66	  __attribute__((__always_inline__))
    67	  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
    68	  { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
    69	
    70	  inline void
    71	  __attribute__((__always_inline__))
    72	  __atomic_add(volatile _Atomic_word* __mem, int __val)
    73	  { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
    74	#else
    75	  _Atomic_word
    76	  __exchange_and_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
    77	
    78	  void
    79	  __atomic_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
    80	#endif
    81	
    82	  inline _Atomic_word
    83	  __attribute__((__always_inline__))
    84	  __exchange_and_add_single(_Atomic_word* __mem, int __val)
    85	  {
    86	    _Atomic_word __result = *__mem;
    87	    *__mem += __val;
    88	    return __result;
    89	  }
    90	
    91	  inline void
    92	  __attribute__((__always_inline__))
    93	  __atomic_add_single(_Atomic_word* __mem, int __val)
    94	  { *__mem += __val; }
    95	
    96	  inline _Atomic_word
    97	  __attribute__ ((__always_inline__))
    98	  __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
    99	  {
   100	    if (__is_single_threaded())
   101	      return __exchange_and_add_single(__mem, __val);
   102	    else
   103	      return __exchange_and_add(__mem, __val);
   104	  }
   105	
   106	  inline void
   107	  __attribute__ ((__always_inline__))
   108	  __atomic_add_dispatch(_Atomic_word* __mem, int __val)
   109	  {
   110	    if (__is_single_threaded())
   111	      __atomic_add_single(__mem, __val);
   112	    else
   113	      __atomic_add(__mem, __val);
   114	  }
   115	
   116	_GLIBCXX_END_NAMESPACE_VERSION
   117	} // namespace
   118	
   119	// Even if the CPU doesn't need a memory barrier, we need to ensure
   120	// that the compiler doesn't reorder memory accesses across the
   121	// barriers.
   122	#ifndef _GLIBCXX_READ_MEM_BARRIER
   123	#define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
   124	#endif
   125	#ifndef _GLIBCXX_WRITE_MEM_BARRIER
   126	#define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
   127	#endif
   128	
   129	#endif