gecko-dev/xpcom/glue/nsWeakReference.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * The contents of this file are subject to the Mozilla Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/MPL/
 * 
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 * 
 * The Original Code is the Mozilla browser.
 * 
 * The Initial Developer of the Original Code is Netscape
 * Communications, Inc.  Portions created by Netscape are
 * Copyright (C) 1999, Mozilla.  All Rights Reserved.
 * 
 * Contributor(s):
 *   Scott Collins <scc@netscape.com>
 */

#ifndef nsWeakReference_h__
#define nsWeakReference_h__

// nsWeakReference.h

#include "nsIWeakReference.h"

class nsWeakReference;

class NS_COM nsSupportsWeakReference : public nsISupportsWeakReference
  {
    public:
      nsSupportsWeakReference()
          : mProxy(0)
        {
          // nothing else to do here
        }

      inline virtual ~nsSupportsWeakReference();

      NS_DECL_NSISUPPORTSWEAKREFERENCE

    private:
      friend class nsWeakReference;

      void
      NoticeProxyDestruction()
          // ...called (only) by an |nsWeakReference| from _its_ dtor.
        {
          mProxy = 0;
        }

      nsWeakReference* mProxy;

		protected:

			inline void ClearWeakReferences();
			PRBool HasWeakReferences() const {return mProxy != 0;}
  };

class NS_COM nsWeakReference : public nsIWeakReference
  {
    public:
    // nsISupports...
      NS_IMETHOD_(nsrefcnt) AddRef();
      NS_IMETHOD_(nsrefcnt) Release();
      NS_IMETHOD QueryInterface( const nsIID&, void** );

    // nsIWeakReference...
      NS_DECL_NSIWEAKREFERENCE

    private:
      friend class nsSupportsWeakReference;

      nsWeakReference( nsSupportsWeakReference* referent )
          : mRefCount(0),
            mReferent(referent)
          // ...I can only be constructed by an |nsSupportsWeakReference|
        {
          // nothing else to do here
        }

    virtual ~nsWeakReference()
           // ...I will only be destroyed by calling |delete| myself.
        {
          if ( mReferent )
            mReferent->NoticeProxyDestruction();
        }

      void
      NoticeReferentDestruction()
          // ...called (only) by an |nsSupportsWeakReference| from _its_ dtor.
        {
          mReferent = 0;
        }

      nsrefcnt                  mRefCount;
      nsSupportsWeakReference*  mReferent;
  };

inline
void
nsSupportsWeakReference::ClearWeakReferences()
		/*
			Usually being called from |nsSupportsWeakReference::~nsSupportsWeakReference|
			will be good enough, but you may have a case where you need to call disconnect
			your weak references in an outer destructor (to prevent some client holding a
			weak reference from re-entering your destructor).
		*/
	{
		if ( mProxy )
			{
				mProxy->NoticeReferentDestruction();
				mProxy = 0;
			}
	}

inline
nsSupportsWeakReference::~nsSupportsWeakReference()
  {
  	ClearWeakReferences();
  }

#endif