Bug 1356556, use of weak references in nsHTMLDNSPrefetch is malloc heavy, so instead use raw pointers and a flag to tell that Link's destructor needs to clear the raw pointer, r=bz

--HG--
extra : rebase_source : f5a60230bfd5c19c82a70069ae59baae69c1f302

dom/base/Link.cpp

@@ -34,6 +34,7 @@ Link::Link(Element *aElement)
   , mNeedsRegistration(false)
   , mRegistered(false)
   , mHasPendingLinkUpdate(false)
+  , mInDNSPrefetch(false)
 {
   MOZ_ASSERT(mElement, "Must have an element");
 }
@@ -45,11 +46,17 @@ Link::Link()
   , mNeedsRegistration(false)
   , mRegistered(false)
   , mHasPendingLinkUpdate(false)
+  , mInDNSPrefetch(false)
 {
 }
 
 Link::~Link()
 {
+  // !mElement is for mock_Link.
+  MOZ_ASSERT(!mElement || !mElement->IsInComposedDoc());
+  if (IsInDNSPrefetch()) {
+    nsHTMLDNSPrefetch::LinkDestroyed(this);
+  }
   UnregisterFromHistory();
 }
 

dom/base/Link.h

@@ -136,6 +136,10 @@ public:
   // If you change this, change also the method in Element.
   virtual void NodeInfoChanged(nsIDocument* aOldDoc) = 0;
 
+  bool IsInDNSPrefetch() { return mInDNSPrefetch; }
+  void SetIsInDNSPrefetch() { mInDNSPrefetch = true; }
+  void ClearIsInDNSPrefetch() { mInDNSPrefetch = false; }
+
 protected:
   virtual ~Link();
 
@@ -179,6 +183,8 @@ private:
   bool mRegistered : 1;
 
   bool mHasPendingLinkUpdate : 1;
+
+  bool mInDNSPrefetch : 1;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(Link, MOZILLA_DOM_LINK_IMPLEMENTATION_IID)

dom/html/nsHTMLDNSPrefetch.cpp

@@ -247,6 +247,15 @@ nsHTMLDNSPrefetch::CancelPrefetchLow(const nsAString &hostname,
                         aReason);
 }
 
+void
+nsHTMLDNSPrefetch::LinkDestroyed(Link* aLink)
+{
+  MOZ_ASSERT(aLink->IsInDNSPrefetch());
+  if (sPrefetches) {
+    // Clean up all the possible links at once.
+    sPrefetches->RemoveUnboundLinks();
+  }
+}
 
 /////////////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -291,6 +300,9 @@ void
 nsHTMLDNSPrefetch::nsDeferrals::Flush()
 {
   while (mHead != mTail) {
+    if (mEntries[mTail].mElement) {
+      mEntries[mTail].mElement->ClearIsInDNSPrefetch();
+    }
     mEntries[mTail].mElement = nullptr;
     mTail = (mTail + 1) & sMaxDeferredMask;
   }
@@ -306,9 +318,10 @@ nsHTMLDNSPrefetch::nsDeferrals::Add(uint16_t flags, Link *aElement)
 
   if (((mHead + 1) & sMaxDeferredMask) == mTail)
     return NS_ERROR_DNS_LOOKUP_QUEUE_FULL;
-    
+
+  aElement->SetIsInDNSPrefetch();
   mEntries[mHead].mFlags = flags;
-  mEntries[mHead].mElement = do_GetWeakReference(aElement);
+  mEntries[mHead].mElement = aElement;
   mHead = (mHead + 1) & sMaxDeferredMask;
 
   if (!mActiveLoaderCount && !mTimerArmed && mTimer) {
@@ -328,9 +341,9 @@ nsHTMLDNSPrefetch::nsDeferrals::SubmitQueue()
   if (!sDNSService) return;
 
   while (mHead != mTail) {
-    nsCOMPtr<nsIContent> content = do_QueryReferent(mEntries[mTail].mElement);
-    if (content) {
-      nsCOMPtr<Link> link = do_QueryInterface(content);
+    nsCOMPtr<Link> link = mEntries[mTail].mElement;
+    if (link) {
+      link->ClearIsInDNSPrefetch();
       // Only prefetch here if request was deferred and deferral not cancelled
       if (link && link->HasDeferredDNSPrefetchRequest()) {
         nsCOMPtr<nsIURI> hrefURI(link ? link->GetURI() : nullptr);
@@ -400,6 +413,20 @@ nsHTMLDNSPrefetch::nsDeferrals::Activate()
     observerService->AddObserver(this, "xpcom-shutdown", true);
 }
 
+void
+nsHTMLDNSPrefetch::nsDeferrals::RemoveUnboundLinks()
+{
+  uint16_t tail = mTail;
+  while (mHead != tail) {
+    if (mEntries[tail].mElement &&
+        !mEntries[tail].mElement->GetElement()->IsInComposedDoc()) {
+      mEntries[tail].mElement->ClearIsInDNSPrefetch();
+      mEntries[tail].mElement = nullptr;
+    }
+    tail = (tail + 1) & sMaxDeferredMask;
+  }
+}
+
 // nsITimer related method
 
 void 

dom/html/nsHTMLDNSPrefetch.h

@@ -63,6 +63,8 @@ public:
   static nsresult CancelPrefetchLow(mozilla::dom::Link *aElement,
                                     nsresult aReason);
 
+  static void LinkDestroyed(mozilla::dom::Link* aLink);
+
 private:
   static nsresult Prefetch(const nsAString &host,
                            const mozilla::OriginAttributes &aOriginAttributes,
@@ -103,6 +105,8 @@ public:
     void Activate();
     nsresult Add(uint16_t flags, mozilla::dom::Link *aElement);
     
+    void RemoveUnboundLinks();
+
   private:
     ~nsDeferrals();
     void Flush();
@@ -123,7 +127,8 @@ public:
     struct deferred_entry
     {
       uint16_t                         mFlags;
-      nsWeakPtr                        mElement;
+      // Link implementation clears this raw pointer in its destructor.
+      mozilla::dom::Link*              mElement;
     } mEntries[sMaxDeferred];
   };