locked_object.h

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#ifndef LOCKED_OBJECT_CLASS
#define LOCKED_OBJECT_CLASS

/*****************************************************************************\
*                                                                             *
*  Name   : locked_object                                                     *
*  Author : Chris Koeritz                                                     *
*                                                                             *
*******************************************************************************
* Copyright (c) 2002-$now By Author.  This program 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 of   *
* the License or (at your option) any later version.  This is online at:      *
*     http://www.fsf.org/copyleft/gpl.html                                    *
* Please send any updates to: fred@gruntose.com                               *
\*****************************************************************************/


#include <basis/function.h>
#ifdef CATCH_ERRORS
  #include <basis/guards.h>
#endif
#include <basis/mutex.h>

template <class contents>
class locked_object
{
public:
  locked_object(contents *object_held = NIL) { _the_object = object_held; }



  ~locked_object() {
    contents *to_zap = swap(NIL);
    WHACK(to_zap);
  }

  contents *lock_object() { _locking.lock(); return _the_object; }

  void unlock_object(contents *to_unlock) {

    if (to_unlock != _the_object) {
#ifdef CATCH_ERRORS
      continuable_error("locked_object", "unlock_object",
          "erroneous pointer has been passed in");
#endif
#ifdef ERRORS_ARE_FATAL
      deadly_error("locked_object", "unlock_object",
          "erroneous pointer has been passed in");
#endif
    }
    if (to_unlock != _the_object) return;
    _locking.unlock();
  }

  contents *swap(contents *new_object) {

    _locking.lock();
    contents *to_return = _the_object;
    _the_object = new_object;
    _locking.unlock();
    return to_return;
  }

private:
  contents *_the_object;  
  mutex _locking;  

  // not permitted.
  locked_object(const locked_object &);
  locked_object &operator =(const locked_object &);
};

#endif

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