libstdc++-v3/libsupc++/guard.cc

   1 // Copyright (C) 2002 Free Software Foundation, Inc.
   2 //
   3 // This file is part of GCC.
   4 //
   5 // GCC is free software; you can redistribute it and/or modify
   6 // it under the terms of the GNU General Public License as published by
   7 // the Free Software Foundation; either version 2, or (at your option)
   8 // any later version.
   9
  10 // GCC is distributed in the hope that it will be useful,
  11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 // GNU General Public License for more details.
  14
  15 // You should have received a copy of the GNU General Public License
  16 // along with GCC; see the file COPYING.  If not, write to
  17 // the Free Software Foundation, 59 Temple Place - Suite 330,
  18 // Boston, MA 02111-1307, USA.
  19
  20 // As a special exception, you may use this file as part of a free software
  21 // library without restriction.  Specifically, if other files instantiate
  22 // templates or use macros or inline functions from this file, or you compile
  23 // this file and link it with other files to produce an executable, this
  24 // file does not by itself cause the resulting executable to be covered by
  25 // the GNU General Public License.  This exception does not however
  26 // invalidate any other reasons why the executable file might be covered by
  27 // the GNU General Public License.
  28
  29 // Written by Mark Mitchell, CodeSourcery LLC, <mark@codesourcery.com>
  30 // Thread support written by Jason Merrill, Red Hat Inc. <jason@redhat.com>
  31
  32 #include <cxxabi.h>
  33 #include <exception>
  34 #include <bits/c++config.h>
  35 #include <bits/gthr.h>
  36 #include <bits/atomicity.h>
  37
  38 // The IA64/generic ABI uses the first byte of the guard variable.
  39 // The ARM EABI uses the least significant bit.
  40
  41 // Thread-safe static local initialization support.
  42 #ifdef __GTHREADS
  43 namespace
  44 {
  45   // static_mutex is a single mutex controlling all static initializations.
  46   // This is a static class--the need for a static initialization function
  47   // to pass to __gthread_once precludes creating multiple instances, though
  48   // I suppose you could achieve the same effect with a template.
  49   class static_mutex
  50   {
  51     static __gthread_recursive_mutex_t mutex;
  52
  53 #ifdef __GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION
  54     static void init();
  55 #endif
  56
  57   public:
  58     static void lock();
  59     static void unlock();
  60   };
  61
  62   __gthread_recursive_mutex_t static_mutex::mutex
  63 #ifdef __GTHREAD_RECURSIVE_MUTEX_INIT
  64   = __GTHREAD_RECURSIVE_MUTEX_INIT
  65 #endif
  66   ;
  67
  68 #ifdef __GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION
  69   void static_mutex::init()
  70   {
  71     __GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION (&mutex);
  72   }
  73 #endif
  74
  75   void static_mutex::lock()
  76   {
  77 #ifdef __GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION
  78     static __gthread_once_t once = __GTHREAD_ONCE_INIT;
  79     __gthread_once (&once, init);
  80 #endif
  81     __gthread_recursive_mutex_lock (&mutex);
  82   }
  83
  84   void static_mutex::unlock ()
  85   {
  86     __gthread_recursive_mutex_unlock (&mutex);
  87   }
  88 }
  89
  90 #ifndef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
  91 inline bool
  92 __test_and_acquire (__cxxabiv1::__guard *g)
  93 {
  94   bool b = _GLIBCXX_GUARD_TEST (g);
  95   _GLIBCXX_READ_MEM_BARRIER;
  96   return b;
  97 }
  98 #define _GLIBCXX_GUARD_TEST_AND_ACQUIRE(G) __test_and_acquire (G)
  99 #endif
 100
 101 #ifndef _GLIBCXX_GUARD_SET_AND_RELEASE
 102 inline void
 103 __set_and_release (__cxxabiv1::__guard *g)
 104 {
 105   _GLIBCXX_WRITE_MEM_BARRIER;
 106   _GLIBCXX_GUARD_SET (g);
 107 }
 108 #define _GLIBCXX_GUARD_SET_AND_RELEASE(G) __set_and_release (G)
 109 #endif
 110
 111 #else /* !__GTHREADS */
 112
 113 #undef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
 114 #undef _GLIBCXX_GUARD_SET_AND_RELEASE
 115 #define _GLIBCXX_GUARD_SET_AND_RELEASE(G) _GLIBCXX_GUARD_SET (G)
 116
 117 #endif /* __GTHREADS */
 118
 119 namespace __gnu_cxx
 120 {
 121   // 6.7[stmt.dcl]/4: If control re-enters the declaration (recursively)
 122   // while the object is being initialized, the behavior is undefined.
 123
 124   // Since we already have a library function to handle locking, we might
 125   // as well check for this situation and throw an exception.
 126   // We use the second byte of the guard variable to remember that we're
 127   // in the middle of an initialization.
 128   class recursive_init: public std::exception
 129   {
 130   public:
 131     recursive_init() throw() { }
 132     virtual ~recursive_init() throw ();
 133   };
 134
 135   recursive_init::~recursive_init() throw() { }
 136 }
 137
 138 namespace __cxxabiv1
 139 {
 140   static inline int
 141   recursion_push (__guard* g)
 142   {
 143     return ((char *)g)[1]++;
 144   }
 145
 146   static inline void
 147   recursion_pop (__guard* g)
 148   {
 149     --((char *)g)[1];
 150   }
 151
 152   static int
 153   acquire_1 (__guard *g)
 154   {
 155     if (_GLIBCXX_GUARD_TEST (g))
 156       return 0;
 157
 158     if (recursion_push (g))
 159       {
 160 #ifdef __EXCEPTIONS
 161         throw __gnu_cxx::recursive_init();
 162 #else
 163         // Use __builtin_trap so we don't require abort().
 164         __builtin_trap ();
 165 #endif
 166       }
 167     return 1;
 168   }
 169
 170   extern "C"
 171   int __cxa_guard_acquire (__guard *g)
 172   {
 173 #ifdef __GTHREADS
 174     // If the target can reorder loads, we need to insert a read memory
 175     // barrier so that accesses to the guarded variable happen after the
 176     // guard test.
 177     if (_GLIBCXX_GUARD_TEST_AND_ACQUIRE (g))
 178       return 0;
 179
 180     if (__gthread_active_p ())
 181       {
 182         // Simple wrapper for exception safety.
 183         struct mutex_wrapper
 184         {
 185           bool unlock;
 186           mutex_wrapper (): unlock(true)
 187           {
 188             static_mutex::lock ();
 189           }
 190           ~mutex_wrapper ()
 191           {
 192             if (unlock)
 193               static_mutex::unlock ();
 194           }
 195         } mw;
 196
 197         if (acquire_1 (g))
 198           {
 199             mw.unlock = false;
 200             return 1;
 201           }
 202
 203         return 0;
 204       }
 205 #endif
 206
 207     return acquire_1 (g);
 208   }
 209
 210   extern "C"
 211   void __cxa_guard_abort (__guard *g)
 212   {
 213     recursion_pop (g);
 214 #ifdef __GTHREADS
 215     if (__gthread_active_p ())
 216       static_mutex::unlock ();
 217 #endif
 218   }
 219
 220   extern "C"
 221   void __cxa_guard_release (__guard *g)
 222   {
 223     recursion_pop (g);
 224     _GLIBCXX_GUARD_SET_AND_RELEASE (g);
 225 #ifdef __GTHREADS
 226     if (__gthread_active_p ())
 227       static_mutex::unlock ();
 228 #endif
 229   }
 230 }