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

   1 // Support for pointer abstractions -*- C++ -*-
   2
   3 // Copyright (C) 2011-2021 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 #include <memory>
  26
  27 #include "mutex_pool.h"
  28
  29 namespace __gnu_internal _GLIBCXX_VISIBILITY(hidden)
  30 {
  31   /* Returns different instances of __mutex depending on the passed index
  32    * in order to limit contention.
  33    */
  34   __gnu_cxx::__mutex&
  35   get_mutex(unsigned char i)
  36   {
  37     // increase alignment to put each lock on a separate cache line
  38     struct alignas(64) M : __gnu_cxx::__mutex { };
  39     static M m[mask + 1];
  40     return m[i];
  41   }
  42 }
  43
  44 namespace std _GLIBCXX_VISIBILITY(default)
  45 {
  46 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  47
  48   bad_weak_ptr::~bad_weak_ptr() noexcept = default;
  49
  50   char const*
  51   bad_weak_ptr::what() const noexcept
  52   { return "bad_weak_ptr"; }
  53
  54 #ifdef __GTHREADS
  55   namespace
  56   {
  57     inline unsigned char key(const void* addr)
  58     { return _Hash_impl::hash(addr) & __gnu_internal::mask; }
  59   }
  60
  61   _Sp_locker::_Sp_locker(const void* p) noexcept
  62   {
  63     if (__gthread_active_p())
  64       {
  65         _M_key1 = _M_key2 = key(p);
  66         __gnu_internal::get_mutex(_M_key1).lock();
  67       }
  68     else
  69       _M_key1 = _M_key2 = __gnu_internal::invalid;
  70   }
  71
  72   _Sp_locker::_Sp_locker(const void* p1, const void* p2) noexcept
  73   {
  74     if (__gthread_active_p())
  75       {
  76         _M_key1 = key(p1);
  77         _M_key2 = key(p2);
  78         if (_M_key2 < _M_key1)
  79           __gnu_internal::get_mutex(_M_key2).lock();
  80         __gnu_internal::get_mutex(_M_key1).lock();
  81         if (_M_key2 > _M_key1)
  82           __gnu_internal::get_mutex(_M_key2).lock();
  83       }
  84     else
  85       _M_key1 = _M_key2 = __gnu_internal::invalid;
  86   }
  87
  88   _Sp_locker::~_Sp_locker()
  89   {
  90     if (_M_key1 != __gnu_internal::invalid)
  91       {
  92         __gnu_internal::get_mutex(_M_key1).unlock();
  93         if (_M_key2 != _M_key1)
  94           __gnu_internal::get_mutex(_M_key2).unlock();
  95       }
  96   }
  97 #endif
  98
  99   bool
 100   _Sp_make_shared_tag::_S_eq(const type_info& ti) noexcept
 101   {
 102 #if __cpp_rtti
 103     return ti == typeid(_Sp_make_shared_tag);
 104 #else
 105     // If libstdc++ itself is built with -fno-rtti then just assume that
 106     // make_shared and allocate_shared will never be used with -frtti.
 107     return false;
 108 #endif
 109   }
 110
 111 _GLIBCXX_END_NAMESPACE_VERSION
 112 } // namespace