libstdc++-v3/include/ext/atomicity.h

   1 // Support for atomic operations -*- C++ -*-
   2
   3 // Copyright (C) 2004-2022 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