stl_threads.h

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00001 // Threading support -*- C++ -*-
00002 
00003 // Copyright (C) 2001, 2002 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 2, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // You should have received a copy of the GNU General Public License along
00017 // with this library; see the file COPYING.  If not, write to the Free
00018 // Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
00019 // USA.
00020 
00021 // As a special exception, you may use this file as part of a free software
00022 // library without restriction.  Specifically, if other files instantiate
00023 // templates or use macros or inline functions from this file, or you compile
00024 // this file and link it with other files to produce an executable, this
00025 // file does not by itself cause the resulting executable to be covered by
00026 // the GNU General Public License.  This exception does not however
00027 // invalidate any other reasons why the executable file might be covered by
00028 // the GNU General Public License.
00029 
00030 /*
00031  * Copyright (c) 1997-1999
00032  * Silicon Graphics Computer Systems, Inc.
00033  *
00034  * Permission to use, copy, modify, distribute and sell this software
00035  * and its documentation for any purpose is hereby granted without fee,
00036  * provided that the above copyright notice appear in all copies and
00037  * that both that copyright notice and this permission notice appear
00038  * in supporting documentation.  Silicon Graphics makes no
00039  * representations about the suitability of this software for any
00040  * purpose.  It is provided "as is" without express or implied warranty.
00041  */
00042 
00043 /** @file stl_threads.h
00044  *  This is an internal header file, included by other library headers.
00045  *  You should not attempt to use it directly.
00046  */
00047 
00048 #ifndef __SGI_STL_INTERNAL_THREADS_H
00049 #define __SGI_STL_INTERNAL_THREADS_H
00050 
00051 // The only supported threading model is GCC's own gthr.h abstraction layer.
00052 #include "bits/gthr.h"
00053 
00054 namespace std
00055 {
00056   // Class _Refcount_Base provides a type, _RC_t, a data member,
00057   // _M_ref_count, and member functions _M_incr and _M_decr, which perform
00058   // atomic preincrement/predecrement.  The constructor initializes 
00059   // _M_ref_count.
00060   struct _Refcount_Base
00061   {
00062     // The type _RC_t
00063     typedef size_t _RC_t;
00064     
00065     // The data member _M_ref_count
00066     volatile _RC_t _M_ref_count;
00067     
00068     // Constructor
00069     __gthread_mutex_t _M_ref_count_lock;
00070 
00071     _Refcount_Base(_RC_t __n) : _M_ref_count(__n)
00072     {
00073 #ifdef __GTHREAD_MUTEX_INIT
00074       __gthread_mutex_t __tmp = __GTHREAD_MUTEX_INIT;
00075       _M_ref_count_lock = __tmp;
00076 #elif defined(__GTHREAD_MUTEX_INIT_FUNCTION)
00077       __GTHREAD_MUTEX_INIT_FUNCTION (&_M_ref_count_lock);
00078 #else
00079 #error __GTHREAD_MUTEX_INIT or __GTHREAD_MUTEX_INIT_FUNCTION should be defined by gthr.h abstraction layer, report problem to libstdc++@gcc.gnu.org.
00080 #endif
00081     }
00082 
00083     void 
00084     _M_incr() 
00085     {
00086       __gthread_mutex_lock(&_M_ref_count_lock);
00087       ++_M_ref_count;
00088       __gthread_mutex_unlock(&_M_ref_count_lock);
00089     }
00090 
00091     _RC_t 
00092     _M_decr() 
00093     {
00094       __gthread_mutex_lock(&_M_ref_count_lock);
00095       volatile _RC_t __tmp = --_M_ref_count;
00096       __gthread_mutex_unlock(&_M_ref_count_lock);
00097       return __tmp;
00098     }
00099   };
00100 
00101   // Atomic swap on unsigned long
00102   // This is guaranteed to behave as though it were atomic only if all
00103   // possibly concurrent updates use _Atomic_swap.
00104   // In some cases the operation is emulated with a lock.
00105 #if defined (__GTHREAD_MUTEX_INIT)
00106   // This could be optimized to use the atomicity.h abstraction layer.
00107   // vyzo: simple _Atomic_swap implementation following the guidelines above
00108   // We use a template here only to get a unique initialized instance.
00109   template<int __dummy>
00110     struct _Swap_lock_struct 
00111     { static __gthread_mutex_t _S_swap_lock; };
00112 
00113   template<int __dummy>
00114     __gthread_mutex_t
00115     _Swap_lock_struct<__dummy>::_S_swap_lock = __GTHREAD_MUTEX_INIT;
00116 
00117   // This should be portable, but performance is expected to be quite
00118   // awful.  This really needs platform specific code.
00119   inline unsigned long 
00120   _Atomic_swap(unsigned long * __p, unsigned long __q) 
00121   {
00122     __gthread_mutex_lock(&_Swap_lock_struct<0>::_S_swap_lock);
00123     unsigned long __result = *__p;
00124     *__p = __q;
00125     __gthread_mutex_unlock(&_Swap_lock_struct<0>::_S_swap_lock);
00126     return __result;
00127   }
00128 #endif
00129 } //namespace std
00130 
00131   // Locking class.  Note that this class *does not have a
00132   // constructor*.  It must be initialized either statically, with
00133   // __STL_MUTEX_INITIALIZER, or dynamically, by explicitly calling
00134   // the _M_initialize member function.  (This is similar to the ways
00135   // that a pthreads mutex can be initialized.)  There are explicit
00136   // member functions for acquiring and releasing the lock.
00137 
00138   // There is no constructor because static initialization is
00139   // essential for some uses, and only a class aggregate (see section
00140   // 8.5.1 of the C++ standard) can be initialized that way.  That
00141   // means we must have no constructors, no base classes, no virtual
00142   // functions, and no private or protected members.
00143 
00144 #if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
00145 namespace __gnu_cxx
00146 {
00147   extern __gthread_mutex_t _GLIBCPP_mutex;
00148   extern __gthread_mutex_t *_GLIBCPP_mutex_address;
00149   extern __gthread_once_t _GLIBCPP_once;
00150   extern void _GLIBCPP_mutex_init (void);
00151   extern void _GLIBCPP_mutex_address_init (void);
00152 }
00153 #endif
00154 
00155 namespace std
00156 {
00157   struct _STL_mutex_lock
00158   {
00159     // The class must be statically initialized with __STL_MUTEX_INITIALIZER.
00160 #if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
00161     volatile int _M_init_flag;
00162     __gthread_once_t _M_once;
00163 #endif
00164     __gthread_mutex_t _M_lock;
00165 
00166     void 
00167     _M_initialize() 
00168     {
00169 #ifdef __GTHREAD_MUTEX_INIT
00170       // There should be no code in this path given the usage rules above.
00171 #elif defined(__GTHREAD_MUTEX_INIT_FUNCTION)
00172       if (_M_init_flag) return;
00173       if (__gthread_once (&__gnu_cxx::_GLIBCPP_once,
00174               __gnu_cxx::_GLIBCPP_mutex_init) != 0
00175       && __gthread_active_p ())
00176     abort ();
00177       __gthread_mutex_lock (&__gnu_cxx::_GLIBCPP_mutex);
00178       if (!_M_init_flag) 
00179     {
00180       // Even though we have a global lock, we use __gthread_once to be
00181       // absolutely certain the _M_lock mutex is only initialized once on
00182       // multiprocessor systems.
00183       __gnu_cxx::_GLIBCPP_mutex_address = &_M_lock;
00184       if (__gthread_once (&_M_once,
00185                   __gnu_cxx::_GLIBCPP_mutex_address_init) != 0
00186         && __gthread_active_p ())
00187         abort ();
00188       _M_init_flag = 1;
00189     }
00190       __gthread_mutex_unlock (&__gnu_cxx::_GLIBCPP_mutex);
00191 #endif
00192     }
00193 
00194     void 
00195     _M_acquire_lock() 
00196     {
00197 #if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
00198       if (!_M_init_flag) _M_initialize();
00199 #endif
00200       __gthread_mutex_lock(&_M_lock);
00201     }
00202 
00203     void 
00204     _M_release_lock() 
00205     {
00206 #if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
00207       if (!_M_init_flag) _M_initialize();
00208 #endif
00209       __gthread_mutex_unlock(&_M_lock);
00210     }
00211   };
00212   
00213 #ifdef __GTHREAD_MUTEX_INIT
00214 #define __STL_MUTEX_INITIALIZER = { __GTHREAD_MUTEX_INIT }
00215 #elif defined(__GTHREAD_MUTEX_INIT_FUNCTION)
00216 #ifdef __GTHREAD_MUTEX_INIT_DEFAULT
00217 #define __STL_MUTEX_INITIALIZER \
00218   = { 0, __GTHREAD_ONCE_INIT, __GTHREAD_MUTEX_INIT_DEFAULT }
00219 #else
00220 #define __STL_MUTEX_INITIALIZER = { 0, __GTHREAD_ONCE_INIT }
00221 #endif
00222 #endif
00223 
00224   // A locking class that uses _STL_mutex_lock.  The constructor takes a
00225   // reference to an _STL_mutex_lock, and acquires a lock.  The
00226   // destructor releases the lock.  It's not clear that this is exactly
00227   // the right functionality.  It will probably change in the future.
00228   struct _STL_auto_lock
00229   {
00230     _STL_mutex_lock& _M_lock;
00231     
00232     _STL_auto_lock(_STL_mutex_lock& __lock) : _M_lock(__lock)
00233     { _M_lock._M_acquire_lock(); }
00234 
00235     ~_STL_auto_lock() { _M_lock._M_release_lock(); }
00236 
00237   private:
00238     void operator=(const _STL_auto_lock&);
00239     _STL_auto_lock(const _STL_auto_lock&);
00240   };
00241   
00242 } // namespace std
00243 
00244 #endif 

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