xpcom/glue/nsWeakReference.cpp

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  23  * Contributor(s):
  24  *   Scott Collins <scc@netscape.com>
  25  *   Pierre Phaneuf <pp@ludusdesign.com>
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  40
  41 // nsWeakReference.cpp
  42
  43 #include "nsWeakReference.h"
  44 #include "nsCOMPtr.h"
  45
  46 class nsWeakReference : public nsIWeakReference
  47   {
  48     public:
  49     // nsISupports...
  50       NS_DECL_ISUPPORTS
  51
  52     // nsIWeakReference...
  53       NS_DECL_NSIWEAKREFERENCE
  54
  55     private:
  56       friend class nsSupportsWeakReference;
  57
  58       nsWeakReference( nsSupportsWeakReference* referent )
  59           : mReferent(referent)
  60           // ...I can only be constructed by an |nsSupportsWeakReference|
  61         {
  62           // nothing else to do here
  63         }
  64
  65       ~nsWeakReference()
  66            // ...I will only be destroyed by calling |delete| myself.
  67         {
  68           if ( mReferent )
  69             mReferent->NoticeProxyDestruction();
  70         }
  71
  72       void
  73       NoticeReferentDestruction()
  74           // ...called (only) by an |nsSupportsWeakReference| from _its_ dtor.
  75         {
  76           mReferent = 0;
  77         }
  78
  79       nsSupportsWeakReference*  mReferent;
  80   };
  81
  82 nsresult
  83 nsQueryReferent::operator()( const nsIID& aIID, void** answer ) const
  84   {
  85     nsresult status;
  86     if ( mWeakPtr )
  87       {
  88         if ( NS_FAILED(status = mWeakPtr->QueryReferent(aIID, answer)) )
  89           *answer = 0;
  90       }
  91     else
  92       status = NS_ERROR_NULL_POINTER;
  93
  94     if ( mErrorPtr )
  95       *mErrorPtr = status;
  96     return status;
  97   }
  98
  99 NS_COM_GLUE nsIWeakReference*  // or else |already_AddRefed<nsIWeakReference>|
 100 NS_GetWeakReference( nsISupports* aInstancePtr, nsresult* aErrorPtr )
 101   {
 102     nsresult status;
 103
 104     nsIWeakReference* result = nsnull;
 105
 106     if ( aInstancePtr )
 107       {
 108         nsCOMPtr<nsISupportsWeakReference> factoryPtr = do_QueryInterface(aInstancePtr, &status);
 109         NS_ASSERTION(factoryPtr, "Oops!  You're asking for a weak reference to an object that doesn't support that.");
 110         if ( factoryPtr )
 111           {
 112             status = factoryPtr->GetWeakReference(&result);
 113           }
 114         // else, |status| has already been set by |do_QueryInterface|
 115       }
 116     else
 117       status = NS_ERROR_NULL_POINTER;
 118
 119     if ( aErrorPtr )
 120       *aErrorPtr = status;
 121     return result;
 122   }
 123
 124 NS_COM_GLUE nsresult
 125 nsSupportsWeakReference::GetWeakReference( nsIWeakReference** aInstancePtr )
 126   {
 127     if ( !aInstancePtr )
 128       return NS_ERROR_NULL_POINTER;
 129
 130     if ( !mProxy )
 131       mProxy = new nsWeakReference(this);
 132     *aInstancePtr = mProxy;
 133
 134     nsresult status;
 135     if ( !*aInstancePtr )
 136       status = NS_ERROR_OUT_OF_MEMORY;
 137     else
 138       {
 139         NS_ADDREF(*aInstancePtr);
 140         status = NS_OK;
 141       }
 142
 143     return status;
 144   }
 145
 146 NS_IMPL_ISUPPORTS1(nsWeakReference, nsIWeakReference)
 147
 148 NS_IMETHODIMP
 149 nsWeakReference::QueryReferent( const nsIID& aIID, void** aInstancePtr )
 150   {
 151     return mReferent ? mReferent->QueryInterface(aIID, aInstancePtr) : NS_ERROR_NULL_POINTER;
 152   }
 153
 154 void
 155 nsSupportsWeakReference::ClearWeakReferences()
 156         {
 157                 if ( mProxy )
 158                         {
 159                                 mProxy->NoticeReferentDestruction();
 160                                 mProxy = 0;
 161                         }
 162         }
 163