Bug 514773. Don't trigger rulenode gc unless we have rulenodes to gc. r=dbaron

layout/style/nsRuleNode.cpp

@@ -876,7 +876,8 @@ nsRuleNode::nsRuleNode(nsPresContext* aContext, nsRuleNode* aParent,
     mRule(aRule),
     mDependentBits((PRUint32(aLevel) << NS_RULE_NODE_LEVEL_SHIFT) |
                    (aIsImportant ? NS_RULE_NODE_IS_IMPORTANT : 0)),
-    mNoneBits(0)
+    mNoneBits(0),
+    mRefCnt(0)
 {
   mChildren.asVoid = nsnull;
   MOZ_COUNT_CTOR(nsRuleNode);
@@ -884,6 +885,13 @@ nsRuleNode::nsRuleNode(nsPresContext* aContext, nsRuleNode* aParent,
 
   NS_ASSERTION(IsRoot() || GetLevel() == aLevel, "not enough bits");
   NS_ASSERTION(IsRoot() || IsImportantRule() == aIsImportant, "yikes");
+  /* If IsRoot(), then aContext->StyleSet() is typically null at this
+     point.  In any case, we don't want to treat the root rulenode as
+     unused.  */
+  if (!IsRoot()) {
+    mParent->AddRef();
+    aContext->StyleSet()->RuleNodeUnused();
+  }
 }
 
 nsRuleNode::~nsRuleNode()
@@ -6192,22 +6200,32 @@ nsRuleNode::Sweep()
   // Call sweep on the children, since some may not be marked, and
   // remove any deleted children from the child lists.
   if (HaveChildren()) {
+    PRUint32 childrenDestroyed;
     if (ChildrenAreHashed()) {
       PLDHashTable *children = ChildrenHash();
+      PRUint32 oldChildCount = children->entryCount;
       PL_DHashTableEnumerate(children, SweepRuleNodeChildren, nsnull);
+      childrenDestroyed = children->entryCount - oldChildCount;
     } else {
+      childrenDestroyed = 0;
       for (nsRuleNode **children = ChildrenListPtr(); *children; ) {
         nsRuleNode *next = (*children)->mNextSibling;
         if ((*children)->Sweep()) {
           // This rule node was destroyed, so implicitly advance by
           // making *children point to the next entry.
           *children = next;
+          ++childrenDestroyed;
         } else {
           // Advance.
           children = &(*children)->mNextSibling;
         }
       }
     }
+    mRefCnt -= childrenDestroyed;
+    NS_POSTCONDITION(IsRoot() || mRefCnt > 0,
+                     "We didn't get swept, so we'd better have style contexts "
+                     "pointing to us or to one of our descendants, which means "
+                     "we'd better have a nonzero mRefCnt here!");
   }
   return PR_FALSE;
 }

layout/style/nsRuleNode.h

@@ -451,6 +451,11 @@ private:
                       // Compute*Data functions don't initialize from
                       // inherited data.
 
+  // Reference count.  This just counts the style contexts that
+  // reference this rulenode.  When this goes to 0 or stops being 0,
+  // we notify the style set.
+  PRUint32 mRefCnt;
+
 public:
   // Overloaded new operator. Initializes the memory to 0 and relies on an arena
   // (which comes from the presShell) to perform the allocation.
@@ -458,6 +463,12 @@ public:
   NS_HIDDEN_(void) Destroy() { DestroyInternal(nsnull); }
   static NS_HIDDEN_(nsILanguageAtomService*) gLangService;
 
+  // Implemented in nsStyleSet.h, since it needs to know about nsStyleSet.
+  inline NS_HIDDEN_(void) AddRef();
+
+  // Implemented in nsStyleSet.h, since it needs to know about nsStyleSet.
+  inline NS_HIDDEN_(void) Release();
+
 protected:
   NS_HIDDEN_(void) DestroyInternal(nsRuleNode ***aDestroyQueueTail);
   NS_HIDDEN_(void) PropagateDependentBit(PRUint32 aBit,

layout/style/nsStyleContext.cpp

@@ -91,6 +91,8 @@ nsStyleContext::nsStyleContext(nsStyleContext* aParent,
   NS_ASSERTION(NS_STYLE_INHERIT_MASK & NS_STYLE_INHERIT_BIT(LastItem),
                "NS_STYLE_INHERIT_MASK must be bigger, and other bits shifted");
   #undef eStyleStruct_LastItem
+
+  mRuleNode->AddRef();
 }
 
 nsStyleContext::~nsStyleContext()
@@ -99,6 +101,8 @@ nsStyleContext::~nsStyleContext()
 
   nsPresContext *presContext = mRuleNode->GetPresContext();
 
+  mRuleNode->Release();
+
   presContext->PresShell()->StyleSet()->
     NotifyStyleContextDestroyed(presContext, this);
 

layout/style/nsStyleSet.cpp

@@ -85,7 +85,7 @@ static const nsStyleSet::sheetType gCSSSheetTypes[] = {
 nsStyleSet::nsStyleSet()
   : mRuleTree(nsnull),
     mRuleWalker(nsnull),
-    mDestroyedCount(0),
+    mUnusedRuleNodeCount(0),
     mBatching(0),
     mInShutdown(PR_FALSE),
     mAuthorStyleDisabled(PR_FALSE),
@@ -905,7 +905,7 @@ nsStyleSet::Shutdown(nsPresContext* aPresContext)
   mDefaultStyleData.Destroy(0, aPresContext);
 }
 
-static const PRInt32 kGCInterval = 1000;
+static const PRInt32 kGCInterval = 300;
 
 void
 nsStyleSet::NotifyStyleContextDestroyed(nsPresContext* aPresContext,
@@ -925,7 +925,7 @@ nsStyleSet::NotifyStyleContextDestroyed(nsPresContext* aPresContext,
   if (mInReconstruct)
     return;
 
-  if (++mDestroyedCount == kGCInterval) {
+  if (mUnusedRuleNodeCount == kGCInterval) {
     GCRuleTrees();
   }
 }
@@ -933,7 +933,7 @@ nsStyleSet::NotifyStyleContextDestroyed(nsPresContext* aPresContext,
 void
 nsStyleSet::GCRuleTrees()
 {
-  mDestroyedCount = 0;
+  mUnusedRuleNodeCount = 0;
 
   // Mark the style context tree by marking all style contexts which
   // have no parent, which will mark all descendants.  This will reach

layout/style/nsStyleSet.h

@@ -248,6 +248,17 @@ class nsStyleSet
   PRBool HasCachedStyleData() const {
     return (mRuleTree && mRuleTree->TreeHasCachedData()) || !mRoots.IsEmpty();
   }
+
+  // Notify the style set that a rulenode is no longer in use, or was
+  // just created and is not in use yet.
+  void RuleNodeUnused() {
+    ++mUnusedRuleNodeCount;
+  }
+
+  // Notify the style set that a rulenode that wasn't in use now is
+  void RuleNodeInUse() {
+    --mUnusedRuleNodeCount;
+  }
   
  private:
   // Not to be implemented
@@ -322,7 +333,7 @@ class nsStyleSet
   nsRuleWalker* mRuleWalker; // This is an instance of a rule walker that can
                              // be used to navigate through our tree.
 
-  PRInt32 mDestroyedCount; // used to batch style context GC
+  PRUint32 mUnusedRuleNodeCount; // used to batch rule node GC
   nsTArray<nsStyleContext*> mRoots; // style contexts with no parent
 
   // Empty style rules to force things that restrict which properties
@@ -343,4 +354,19 @@ class nsStyleSet
 
 };
 
+inline
+NS_HIDDEN_(void) nsRuleNode::AddRef()
+{
+  if (mRefCnt++ == 0 && !IsRoot()) {
+    mPresContext->StyleSet()->RuleNodeInUse();
+  }
+}
+
+inline
+NS_HIDDEN_(void) nsRuleNode::Release()
+{
+  if (--mRefCnt == 0 && !IsRoot()) {
+    mPresContext->StyleSet()->RuleNodeUnused();
+  }
+}
 #endif