xpcom/glue/nsWeakReference.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 // nsWeakReference.cpp
   8
   9 #include "mozilla/Attributes.h"
  10
  11 #include "nsWeakReference.h"
  12 #include "nsCOMPtr.h"
  13
  14 class nsWeakReference MOZ_FINAL : public nsIWeakReference
  15 {
  16 public:
  17   // nsISupports...
  18   NS_DECL_ISUPPORTS
  19
  20   // nsIWeakReference...
  21   NS_DECL_NSIWEAKREFERENCE
  22   virtual size_t SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const;
  23
  24 private:
  25   friend class nsSupportsWeakReference;
  26
  27   explicit nsWeakReference(nsSupportsWeakReference* aReferent)
  28     : mReferent(aReferent)
  29     // ...I can only be constructed by an |nsSupportsWeakReference|
  30   {
  31   }
  32
  33   ~nsWeakReference()
  34   // ...I will only be destroyed by calling |delete| myself.
  35   {
  36     if (mReferent) {
  37       mReferent->NoticeProxyDestruction();
  38     }
  39   }
  40
  41   void
  42   NoticeReferentDestruction()
  43   // ...called (only) by an |nsSupportsWeakReference| from _its_ dtor.
  44   {
  45     mReferent = 0;
  46   }
  47
  48   nsSupportsWeakReference*  mReferent;
  49 };
  50
  51 nsresult
  52 nsQueryReferent::operator()(const nsIID& aIID, void** aAnswer) const
  53 {
  54   nsresult status;
  55   if (mWeakPtr) {
  56     if (NS_FAILED(status = mWeakPtr->QueryReferent(aIID, aAnswer))) {
  57       *aAnswer = 0;
  58     }
  59   } else {
  60     status = NS_ERROR_NULL_POINTER;
  61   }
  62
  63   if (mErrorPtr) {
  64     *mErrorPtr = status;
  65   }
  66   return status;
  67 }
  68
  69 nsIWeakReference*  // or else |already_AddRefed<nsIWeakReference>|
  70 NS_GetWeakReference(nsISupports* aInstancePtr, nsresult* aErrorPtr)
  71 {
  72   nsresult status;
  73
  74   nsIWeakReference* result = nullptr;
  75
  76   if (aInstancePtr) {
  77     nsCOMPtr<nsISupportsWeakReference> factoryPtr =
  78       do_QueryInterface(aInstancePtr, &status);
  79     if (factoryPtr) {
  80       status = factoryPtr->GetWeakReference(&result);
  81     }
  82     // else, |status| has already been set by |do_QueryInterface|
  83   } else {
  84     status = NS_ERROR_NULL_POINTER;
  85   }
  86
  87   if (aErrorPtr) {
  88     *aErrorPtr = status;
  89   }
  90   return result;
  91 }
  92
  93 nsresult
  94 nsSupportsWeakReference::GetWeakReference(nsIWeakReference** aInstancePtr)
  95 {
  96   if (!aInstancePtr) {
  97     return NS_ERROR_NULL_POINTER;
  98   }
  99
 100   if (!mProxy) {
 101     mProxy = new nsWeakReference(this);
 102   }
 103   *aInstancePtr = mProxy;
 104
 105   nsresult status;
 106   if (!*aInstancePtr) {
 107     status = NS_ERROR_OUT_OF_MEMORY;
 108   } else {
 109     NS_ADDREF(*aInstancePtr);
 110     status = NS_OK;
 111   }
 112
 113   return status;
 114 }
 115
 116 NS_IMPL_ISUPPORTS(nsWeakReference, nsIWeakReference)
 117
 118 NS_IMETHODIMP
 119 nsWeakReference::QueryReferent(const nsIID& aIID, void** aInstancePtr)
 120 {
 121   return mReferent ? mReferent->QueryInterface(aIID, aInstancePtr) :
 122                      NS_ERROR_NULL_POINTER;
 123 }
 124
 125 size_t
 126 nsWeakReference::SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const
 127 {
 128   return aMallocSizeOf(this);
 129 }
 130
 131 void
 132 nsSupportsWeakReference::ClearWeakReferences()
 133 {
 134   if (mProxy) {
 135     mProxy->NoticeReferentDestruction();
 136     mProxy = 0;
 137   }
 138 }
 139