libstdc++-v3/src/c++11/mutex.cc

   1 // mutex -*- C++ -*-
   2
   3 // Copyright (C) 2008-2019 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 #include <mutex>
  26
  27 #ifdef _GLIBCXX_HAS_GTHREADS
  28 #ifndef _GLIBCXX_HAVE_TLS
  29 namespace
  30 {
  31   inline std::unique_lock<std::mutex>*&
  32   __get_once_functor_lock_ptr()
  33   {
  34     static std::unique_lock<std::mutex>* __once_functor_lock_ptr = 0;
  35     return __once_functor_lock_ptr;
  36   }
  37 }
  38 #endif
  39
  40 namespace std _GLIBCXX_VISIBILITY(default)
  41 {
  42 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  43
  44 #ifdef _GLIBCXX_HAVE_TLS
  45   __thread void* __once_callable;
  46   __thread void (*__once_call)();
  47 #else
  48   // Explicit instantiation due to -fno-implicit-instantiation.
  49   template class function<void()>;
  50   function<void()> __once_functor;
  51
  52   mutex&
  53   __get_once_mutex()
  54   {
  55     static mutex once_mutex;
  56     return once_mutex;
  57   }
  58
  59   // code linked against ABI 3.4.12 and later uses this
  60   void
  61   __set_once_functor_lock_ptr(unique_lock<mutex>* __ptr)
  62   {
  63     __get_once_functor_lock_ptr() = __ptr;
  64   }
  65
  66   // unsafe - retained for compatibility with ABI 3.4.11
  67   unique_lock<mutex>&
  68   __get_once_functor_lock()
  69   {
  70     static unique_lock<mutex> once_functor_lock(__get_once_mutex(), defer_lock);
  71     return once_functor_lock;
  72   }
  73 #endif
  74
  75   extern "C"
  76   {
  77     void __once_proxy()
  78     {
  79 #ifndef _GLIBCXX_HAVE_TLS
  80       function<void()> __once_call = std::move(__once_functor);
  81       if (unique_lock<mutex>* __lock = __get_once_functor_lock_ptr())
  82       {
  83         // caller is using new ABI and provided lock ptr
  84         __get_once_functor_lock_ptr() = 0;
  85         __lock->unlock();
  86       }
  87       else
  88         __get_once_functor_lock().unlock();  // global lock
  89 #endif
  90       __once_call();
  91     }
  92   }
  93
  94 _GLIBCXX_END_NAMESPACE_VERSION
  95 } // namespace std
  96
  97 #endif // _GLIBCXX_HAS_GTHREADS