Bug 1393592 - manually de-virtualize nsIWeakReference::QueryReferent; r=ehsan

The virtual call to this method shows up in profiles, and therefore
would be nice to avoid if possible.  We can do that by making
nsIWeakReference hold the weak reference itself and therefore
implementing a non-virtual QueryReferent method.

Author: froydnj

dom/base/FragmentOrElement.cpp

@@ -693,18 +693,19 @@ NS_IMPL_ISUPPORTS(nsNodeWeakReference,
 
 nsNodeWeakReference::~nsNodeWeakReference()
 {
-  if (mNode) {
-    NS_ASSERTION(mNode->Slots()->mWeakReference == this,
+  nsINode* node = static_cast<nsINode*>(mObject);
+
+  if (node) {
+    NS_ASSERTION(node->Slots()->mWeakReference == this,
                  "Weak reference has wrong value");
-    mNode->Slots()->mWeakReference = nullptr;
+    node->Slots()->mWeakReference = nullptr;
   }
 }
 
 NS_IMETHODIMP
-nsNodeWeakReference::QueryReferent(const nsIID& aIID, void** aInstancePtr)
+nsNodeWeakReference::QueryReferentFromScript(const nsIID& aIID, void** aInstancePtr)
 {
-  return mNode ? mNode->QueryInterface(aIID, aInstancePtr) :
-                 NS_ERROR_NULL_POINTER;
+  return QueryReferent(aIID, aInstancePtr);
 }
 
 size_t

dom/base/FragmentOrElement.h

@@ -53,7 +53,7 @@ class nsNodeWeakReference final : public nsIWeakReference
 {
 public:
   explicit nsNodeWeakReference(nsINode* aNode)
-    : mNode(aNode)
+    : nsIWeakReference(aNode)
   {
   }
 
@@ -63,17 +63,14 @@ class nsNodeWeakReference final : public nsIWeakReference
   // nsIWeakReference
   NS_DECL_NSIWEAKREFERENCE
   virtual size_t SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const override;
-  virtual bool IsAlive() const override { return mNode != nullptr; }
 
   void NoticeNodeDestruction()
   {
-    mNode = nullptr;
+    mObject = nullptr;
   }
 
 private:
   ~nsNodeWeakReference();
-
-  nsINode* MOZ_NON_OWNING_REF mNode;
 };
 
 /**

xpcom/base/nsIWeakReference.idl

@@ -7,7 +7,28 @@
 #include "nsISupports.idl"
 
 %{C++
+#include "mozilla/Attributes.h"
 #include "mozilla/MemoryReporting.h"
+
+// For MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED.
+#include "nsDebug.h"
+
+#ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
+
+#define MOZ_WEAKREF_DECL_OWNINGTHREAD nsAutoOwningThread _mWeakRefOwningThread;
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD \
+  _mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) \
+  (that)->_mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")
+
+#else
+
+#define MOZ_WEAKREF_DECL_OWNINGTHREAD
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD do { } while (false)
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) do { } while (false)
+
+#endif
+
 %}
 
 /**
@@ -33,15 +54,36 @@ interface nsIWeakReference : nsISupports
      * like (a proxied) |QueryInterface|.  Don't hold on to the produced interface permanently;
      * that would defeat the purpose of using a non-owning |nsIWeakReference| in the first place.
      */
+    [binaryname(QueryReferentFromScript)]
     void QueryReferent( in nsIIDRef uuid, [iid_is(uuid), retval] out nsQIResult result );
 
 %{C++
-    virtual size_t SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const = 0;
+  virtual size_t SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const = 0;
 
-    /**
-     * Returns true if the referring object is alive.  Otherwise, false.
-     */
-    virtual bool IsAlive() const = 0;
+  /**
+   * Returns true if the referring object is alive.  Otherwise, false.
+   */
+  bool IsAlive() const
+  {
+    return !!mObject;
+  }
+
+  nsresult QueryReferent(const nsIID& aIID, void** aInstancePtr);
+
+protected:
+  friend class nsSupportsWeakReference;
+
+  nsIWeakReference(nsISupports* aObject)
+    : mObject(aObject)
+  {
+  }
+
+  nsIWeakReference() = delete;
+
+  MOZ_WEAKREF_DECL_OWNINGTHREAD
+
+  // The object we're holding a weak reference to.
+  nsISupports* MOZ_NON_OWNING_REF mObject;
 %}
   };
 

xpcom/base/nsWeakReference.cpp

@@ -12,22 +12,6 @@
 #include "nsCOMPtr.h"
 #include "nsDebug.h"
 
-#ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
-
-#define MOZ_WEAKREF_DECL_OWNINGTHREAD nsAutoOwningThread _mWeakRefOwningThread;
-#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD \
-  _mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")
-#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) \
-  (that)->_mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")
-
-#else
-
-#define MOZ_WEAKREF_DECL_OWNINGTHREAD
-#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD do { } while (false)
-#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) do { } while (false)
-
-#endif
-
 class nsWeakReference final : public nsIWeakReference
 {
 public:
@@ -37,15 +21,12 @@ class nsWeakReference final : public nsIWeakReference
   // nsIWeakReference...
   NS_DECL_NSIWEAKREFERENCE
   size_t SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const override;
-  bool IsAlive() const override { return mReferent != nullptr; }
 
 private:
-  MOZ_WEAKREF_DECL_OWNINGTHREAD
-
   friend class nsSupportsWeakReference;
 
   explicit nsWeakReference(nsSupportsWeakReference* aReferent)
-    : mReferent(aReferent)
+    : nsIWeakReference(aReferent)
     // ...I can only be constructed by an |nsSupportsWeakReference|
   {
   }
@@ -54,8 +35,8 @@ class nsWeakReference final : public nsIWeakReference
   // ...I will only be destroyed by calling |delete| myself.
   {
     MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
-    if (mReferent) {
-      mReferent->NoticeProxyDestruction();
+    if (mObject) {
+      static_cast<nsSupportsWeakReference*>(mObject)->NoticeProxyDestruction();
     }
   }
 
@@ -64,10 +45,8 @@ class nsWeakReference final : public nsIWeakReference
   // ...called (only) by an |nsSupportsWeakReference| from _its_ dtor.
   {
     MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
-    mReferent = nullptr;
+    mObject = nullptr;
   }
-
-  nsSupportsWeakReference* MOZ_NON_OWNING_REF mReferent;
 };
 
 nsresult
@@ -140,12 +119,21 @@ nsSupportsWeakReference::GetWeakReference(nsIWeakReference** aInstancePtr)
 NS_IMPL_ISUPPORTS(nsWeakReference, nsIWeakReference)
 
 NS_IMETHODIMP
-nsWeakReference::QueryReferent(const nsIID& aIID, void** aInstancePtr)
+nsWeakReference::QueryReferentFromScript(const nsIID& aIID, void** aInstancePtr)
+{
+  return QueryReferent(aIID, aInstancePtr);
+}
+
+nsresult
+nsIWeakReference::QueryReferent(const nsIID& aIID, void** aInstancePtr)
 {
   MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
 
-  return mReferent ? mReferent->QueryInterface(aIID, aInstancePtr) :
-                     NS_ERROR_NULL_POINTER;
+  if (!mObject) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
+  return mObject->QueryInterface(aIID, aInstancePtr);
 }
 
 size_t