source: vbox/trunk/src/libs/xpcom18a4/xpcom/glue/nsWeakReference.h@ 31232

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
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 * 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
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 * 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 the Initial Developer are Copyright (C) 1999
 * the Initial Developer. All Rights Reserved.
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 * Contributor(s):
 *   Scott Collins <[email protected]>
 *
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#ifndef nsWeakReference_h__
#define nsWeakReference_h__

// nsWeakReference.h

#include "nsIWeakReference.h"

class nsWeakReference;

#undef  IMETHOD_VISIBILITY
#define IMETHOD_VISIBILITY NS_VISIBILITY_DEFAULT

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

      NS_DECL_NSISUPPORTSWEAKREFERENCE

    protected:
      inline ~nsSupportsWeakReference();

    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;}
  };

#undef  IMETHOD_VISIBILITY
#define IMETHOD_VISIBILITY NS_VISIBILITY_HIDDEN

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
        }

      ~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