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       1             : // Support for atomic operations -*- C++ -*-
       2             : 
       3             : // Copyright (C) 2004-2019 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             : 
      38             : namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
      39             : {
      40             : _GLIBCXX_BEGIN_NAMESPACE_VERSION
      41             : 
      42             :   // Functions for portable atomic access.
      43             :   // To abstract locking primitives across all thread policies, use:
      44             :   // __exchange_and_add_dispatch
      45             :   // __atomic_add_dispatch
      46             : #ifdef _GLIBCXX_ATOMIC_BUILTINS
      47             :   static inline _Atomic_word 
      48        1910 :   __exchange_and_add(volatile _Atomic_word* __mem, int __val)
      49        1910 :   { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
      50             : 
      51             :   static inline void
      52             :   __atomic_add(volatile _Atomic_word* __mem, int __val)
      53             :   { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
      54             : #else
      55             :   _Atomic_word
      56             :   __attribute__ ((__unused__))
      57             :   __exchange_and_add(volatile _Atomic_word*, int) throw ();
      58             : 
      59             :   void
      60             :   __attribute__ ((__unused__))
      61             :   __atomic_add(volatile _Atomic_word*, int) throw ();
      62             : #endif
      63             : 
      64             :   static inline _Atomic_word
      65           0 :   __exchange_and_add_single(_Atomic_word* __mem, int __val)
      66             :   {
      67           0 :     _Atomic_word __result = *__mem;
      68           0 :     *__mem += __val;
      69           0 :     return __result;
      70             :   }
      71             : 
      72             :   static inline void
      73             :   __atomic_add_single(_Atomic_word* __mem, int __val)
      74             :   { *__mem += __val; }
      75             : 
      76             :   static inline _Atomic_word
      77             :   __attribute__ ((__unused__))
      78        1910 :   __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
      79             :   {
      80             : #ifdef __GTHREADS
      81        1910 :     if (__gthread_active_p())
      82        1910 :       return __exchange_and_add(__mem, __val);
      83             :     else
      84           0 :       return __exchange_and_add_single(__mem, __val);
      85             : #else
      86             :     return __exchange_and_add_single(__mem, __val);
      87             : #endif
      88             :   }
      89             : 
      90             :   static inline void
      91             :   __attribute__ ((__unused__))
      92             :   __atomic_add_dispatch(_Atomic_word* __mem, int __val)
      93             :   {
      94             : #ifdef __GTHREADS
      95             :     if (__gthread_active_p())
      96             :       __atomic_add(__mem, __val);
      97             :     else
      98             :       __atomic_add_single(__mem, __val);
      99             : #else
     100             :     __atomic_add_single(__mem, __val);
     101             : #endif
     102             :   }
     103             : 
     104             : _GLIBCXX_END_NAMESPACE_VERSION
     105             : } // namespace
     106             : 
     107             : // Even if the CPU doesn't need a memory barrier, we need to ensure
     108             : // that the compiler doesn't reorder memory accesses across the
     109             : // barriers.
     110             : #ifndef _GLIBCXX_READ_MEM_BARRIER
     111             : #define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
     112             : #endif
     113             : #ifndef _GLIBCXX_WRITE_MEM_BARRIER
     114             : #define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
     115             : #endif
     116             : 
     117             : #endif