xpcom/base/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 #include "nsDebug.h"
  14
  15 class nsWeakReference final : public nsIWeakReference {
  16  public:
  17   // nsISupports...
  18   NS_DECL_ISUPPORTS
  19
  20   // nsIWeakReference...
  21   NS_DECL_NSIWEAKREFERENCE
  22   size_t SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const override;
  23
  24  private:
  25   friend class nsSupportsWeakReference;
  26
  27   explicit nsWeakReference(nsSupportsWeakReference* aReferent)
  28       : nsIWeakReference(aReferent)
  29   // ...I can only be constructed by an |nsSupportsWeakReference|
  30   {}
  31
  32   ~nsWeakReference()
  33   // ...I will only be destroyed by calling |delete| myself.
  34   {
  35     MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
  36     if (mObject) {
  37       static_cast<nsSupportsWeakReference*>(mObject)->NoticeProxyDestruction();
  38     }
  39   }
  40
  41   void NoticeReferentDestruction()
  42   // ...called (only) by an |nsSupportsWeakReference| from _its_ dtor.
  43   {
  44     MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
  45     mObject = nullptr;
  46   }
  47 };
  48
  49 nsresult nsQueryReferent::operator()(const nsIID& aIID, void** aAnswer) const {
  50   nsresult status;
  51   if (mWeakPtr) {
  52     if (NS_FAILED(status = mWeakPtr->QueryReferent(aIID, aAnswer))) {
  53       *aAnswer = 0;
  54     }
  55   } else {
  56     status = NS_ERROR_NULL_POINTER;
  57   }
  58
  59   if (mErrorPtr) {
  60     *mErrorPtr = status;
  61   }
  62   return status;
  63 }
  64
  65 nsIWeakReference* NS_GetWeakReference(nsISupportsWeakReference* aInstancePtr,
  66                                       nsresult* aErrorPtr) {
  67   nsresult status;
  68
  69   nsIWeakReference* result = nullptr;
  70
  71   if (aInstancePtr) {
  72     status = aInstancePtr->GetWeakReference(&result);
  73   } else {
  74     status = NS_ERROR_NULL_POINTER;
  75   }
  76
  77   if (aErrorPtr) {
  78     *aErrorPtr = status;
  79   }
  80
  81   return result;
  82 }
  83
  84 nsIWeakReference*  // or else |already_AddRefed<nsIWeakReference>|
  85 NS_GetWeakReference(nsISupports* aInstancePtr, nsresult* aErrorPtr) {
  86   nsresult status;
  87
  88   nsIWeakReference* result = nullptr;
  89
  90   if (aInstancePtr) {
  91     nsCOMPtr<nsISupportsWeakReference> factoryPtr =
  92         do_QueryInterface(aInstancePtr, &status);
  93     if (factoryPtr) {
  94       status = factoryPtr->GetWeakReference(&result);
  95     }
  96     // else, |status| has already been set by |do_QueryInterface|
  97   } else {
  98     status = NS_ERROR_NULL_POINTER;
  99   }
 100
 101   if (aErrorPtr) {
 102     *aErrorPtr = status;
 103   }
 104   return result;
 105 }
 106
 107 nsresult nsSupportsWeakReference::GetWeakReference(
 108     nsIWeakReference** aInstancePtr) {
 109   if (!aInstancePtr) {
 110     return NS_ERROR_NULL_POINTER;
 111   }
 112
 113   if (!mProxy) {
 114     mProxy = new nsWeakReference(this);
 115   } else {
 116     MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(mProxy);
 117   }
 118   *aInstancePtr = mProxy;
 119
 120   nsresult status;
 121   if (!*aInstancePtr) {
 122     status = NS_ERROR_OUT_OF_MEMORY;
 123   } else {
 124     NS_ADDREF(*aInstancePtr);
 125     status = NS_OK;
 126   }
 127
 128   return status;
 129 }
 130
 131 NS_IMPL_ISUPPORTS(nsWeakReference, nsIWeakReference)
 132
 133 NS_IMETHODIMP
 134 nsWeakReference::QueryReferentFromScript(const nsIID& aIID,
 135                                          void** aInstancePtr) {
 136   return QueryReferent(aIID, aInstancePtr);
 137 }
 138
 139 nsresult nsIWeakReference::QueryReferent(const nsIID& aIID,
 140                                          void** aInstancePtr) {
 141   MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
 142
 143   if (!mObject) {
 144     return NS_ERROR_NULL_POINTER;
 145   }
 146
 147   return mObject->QueryInterface(aIID, aInstancePtr);
 148 }
 149
 150 size_t nsWeakReference::SizeOfOnlyThis(
 151     mozilla::MallocSizeOf aMallocSizeOf) const {
 152   return aMallocSizeOf(this);
 153 }
 154
 155 void nsSupportsWeakReference::ClearWeakReferences() {
 156   if (mProxy) {
 157     mProxy->NoticeReferentDestruction();
 158     mProxy = nullptr;
 159   }
 160 }