libstdc++-v3/include/bits/stl_threads.h

// Threading support -*- C++ -*-

// Copyright (C) 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

/*
 * Copyright (c) 1997-1999
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file stl_threads.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef _STL_THREADS_H
#define _STL_THREADS_H 1

#include <cstddef>

// The only supported threading model is GCC's own gthr.h abstraction
// layer.
#include "bits/gthr.h"

namespace __gnu_internal
{
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
  extern __gthread_mutex_t _GLIBCXX_mutex;
  extern __gthread_mutex_t *_GLIBCXX_mutex_address;
  extern __gthread_once_t _GLIBCXX_once;
  extern void _GLIBCXX_mutex_init(void);
  extern void _GLIBCXX_mutex_address_init(void);
#endif
} // namespace __gnu_internal

namespace __gnu_cxx
{
  // Locking class.  Note that this class *does not have a
  // constructor*.  It must be initialized either statically, with
  // __STL_MUTEX_INITIALIZER, or dynamically, by explicitly calling
  // the _M_initialize member function.  (This is similar to the ways
  // that a pthreads mutex can be initialized.)  There are explicit
  // member functions for acquiring and releasing the lock.

  // There is no constructor because static initialization is
  // essential for some uses, and only a class aggregate (see section
  // 8.5.1 of the C++ standard) can be initialized that way.  That
  // means we must have no constructors, no base classes, no virtual
  // functions, and no private or protected members.
  struct _STL_mutex_lock
  {
    // The class must be statically initialized with __STL_MUTEX_INITIALIZER.
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
    volatile int _M_init_flag;
    __gthread_once_t _M_once;
#endif
    __gthread_mutex_t _M_lock;

    void
    _M_initialize()
    {
#ifdef __GTHREAD_MUTEX_INIT
      // There should be no code in this path given the usage rules above.
#elif defined(__GTHREAD_MUTEX_INIT_FUNCTION)
      if (_M_init_flag) return;
      if (__gthread_once(&__gnu_internal::_GLIBCXX_once,
			 __gnu_internal::_GLIBCXX_mutex_init) != 0
	  && __gthread_active_p())
	abort ();
      __gthread_mutex_lock(&__gnu_internal::_GLIBCXX_mutex);
      if (!_M_init_flag)
	{
	  // Even though we have a global lock, we use __gthread_once to be
	  // absolutely certain the _M_lock mutex is only initialized once on
	  // multiprocessor systems.
	  __gnu_internal::_GLIBCXX_mutex_address = &_M_lock;
	  if (__gthread_once(&_M_once,
			     __gnu_internal::_GLIBCXX_mutex_address_init) != 0
	    && __gthread_active_p())
	    abort();
	  _M_init_flag = 1;
	}
      __gthread_mutex_unlock(&__gnu_internal::_GLIBCXX_mutex);
#endif
    }

    void
    _M_acquire_lock()
    {
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
      if (!_M_init_flag) _M_initialize();
#endif
      __gthread_mutex_lock(&_M_lock);
    }

    void
    _M_release_lock()
    {
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
      if (!_M_init_flag) _M_initialize();
#endif
      __gthread_mutex_unlock(&_M_lock);
    }
  };

#ifdef __GTHREAD_MUTEX_INIT
#define __STL_MUTEX_INITIALIZER = { __GTHREAD_MUTEX_INIT }
#elif defined(__GTHREAD_MUTEX_INIT_FUNCTION)
#ifdef __GTHREAD_MUTEX_INIT_DEFAULT
#define __STL_MUTEX_INITIALIZER \
  = { 0, __GTHREAD_ONCE_INIT, __GTHREAD_MUTEX_INIT_DEFAULT }
#else
#define __STL_MUTEX_INITIALIZER = { 0, __GTHREAD_ONCE_INIT }
#endif
#endif
} // namespace __gnu_cxx

#endif