From 3a1c8cd8d306c6c3c6f2a272060af95196e09ce1 Mon Sep 17 00:00:00 2001
From: Andrew McCreight <amccreight@mozilla.com>
Date: Tue, 30 Apr 2013 10:41:23 -0700
Subject: [PATCH] Bug 716716 - Add templated way to iterate over purple buffer
 entries. r=smaug

---
 xpcom/base/nsCycleCollector.cpp | 155 +++++++++++++++++++-------------
 1 file changed, 93 insertions(+), 62 deletions(-)

diff --git a/xpcom/base/nsCycleCollector.cpp b/xpcom/base/nsCycleCollector.cpp
index f192f60368c..c4fd459881f 100644
--- a/xpcom/base/nsCycleCollector.cpp
+++ b/xpcom/base/nsCycleCollector.cpp
@@ -689,9 +689,18 @@ private:
                 "ill-sized nsPurpleBuffer::Block"
             );
         }
-        void StaticAsserts();
+
+        template <class PurpleVisitor>
+        void VisitEntries(nsPurpleBuffer &aBuffer, PurpleVisitor &aVisitor)
+        {
+            nsPurpleBufferEntry *eEnd = ArrayEnd(mEntries);
+            for (nsPurpleBufferEntry *e = mEntries; e != eEnd; ++e) {
+                if (!(uintptr_t(e->mObject) & uintptr_t(1))) {
+                    aVisitor.Visit(aBuffer, e);
+                }
+            }
+        }
     };
-public:
     // This class wraps a linked list of the elements in the purple
     // buffer.
 
@@ -700,6 +709,7 @@ public:
     Block mFirstBlock;
     nsPurpleBufferEntry *mFreeList;
 
+public:
     nsPurpleBuffer(nsCycleCollectorParams &params)
         : mParams(params)
     {
@@ -711,6 +721,14 @@ public:
         FreeBlocks();
     }
 
+    template <class PurpleVisitor>
+    void VisitEntries(PurpleVisitor &aVisitor)
+    {
+        for (Block *b = &mFirstBlock; b; b = b->mNext) {
+            b->VisitEntries(*this, aVisitor);
+        }
+    }
+
     void InitBlocks()
     {
         mCount = 0;
@@ -748,25 +766,25 @@ public:
         mFirstBlock.mNext = nullptr;
     }
 
-    void UnmarkRemainingPurple(Block *b)
+    struct UnmarkRemainingPurpleVisitor
     {
-        for (nsPurpleBufferEntry *e = b->mEntries,
-                              *eEnd = ArrayEnd(b->mEntries);
-             e != eEnd; ++e) {
-            if (!(uintptr_t(e->mObject) & uintptr_t(1))) {
-                // This is a real entry (rather than something on the
-                // free list).
-                if (e->mObject) {
-                    void *obj = e->mObject;
-                    nsCycleCollectionParticipant *cp = e->mParticipant;
-                    CanonicalizeParticipant(&obj, &cp);
-                    cp->UnmarkIfPurple(obj);
-                }
-
-                if (--mCount == 0)
-                    break;
+        void
+        Visit(nsPurpleBuffer &aBuffer, nsPurpleBufferEntry *aEntry)
+        {
+            if (aEntry->mObject) {
+                void *obj = aEntry->mObject;
+                nsCycleCollectionParticipant *cp = aEntry->mParticipant;
+                CanonicalizeParticipant(&obj, &cp);
+                cp->UnmarkIfPurple(obj);
+                --aBuffer.mCount;
             }
         }
+    };
+
+    void UnmarkRemainingPurple(Block *b)
+    {
+        UnmarkRemainingPurpleVisitor visitor;
+        b->VisitEntries(*this, visitor);
     }
 
     void SelectPointers(GCGraphBuilder &builder);
@@ -859,32 +877,38 @@ public:
 static bool
 AddPurpleRoot(GCGraphBuilder &builder, void *root, nsCycleCollectionParticipant *cp);
 
-void
-nsPurpleBuffer::SelectPointers(GCGraphBuilder &aBuilder)
+struct SelectPointersVisitor
 {
-    // Walk through all the blocks.
-    for (Block *b = &mFirstBlock; b; b = b->mNext) {
-        for (nsPurpleBufferEntry *e = b->mEntries,
-                              *eEnd = ArrayEnd(b->mEntries);
-            e != eEnd; ++e) {
-            if (!(uintptr_t(e->mObject) & uintptr_t(1))) {
-                // This is a real entry (rather than something on the
-                // free list).
-                if (e->mObject && e->mNotPurple) {
-                    void* o = e->mObject;
-                    nsCycleCollectionParticipant* cp = e->mParticipant;
-                    CanonicalizeParticipant(&o, &cp);
-                    cp->UnmarkIfPurple(o);
-                    Remove(e);
-                } else if (!e->mObject || AddPurpleRoot(aBuilder, e->mObject,
-                                                        e->mParticipant)) {
-                    Remove(e);
-                }
-            }
+    SelectPointersVisitor(GCGraphBuilder &aBuilder)
+        : mBuilder(aBuilder)
+    {}
+
+    void
+    Visit(nsPurpleBuffer &aBuffer, nsPurpleBufferEntry *aEntry)
+    {
+        if (aEntry->mObject && aEntry->mNotPurple) {
+            void* o = aEntry->mObject;
+            nsCycleCollectionParticipant* cp = aEntry->mParticipant;
+            CanonicalizeParticipant(&o, &cp);
+            cp->UnmarkIfPurple(o);
+            aBuffer.Remove(aEntry);
+        } else if (!aEntry->mObject ||
+                   AddPurpleRoot(mBuilder, aEntry->mObject, aEntry->mParticipant)) {
+            aBuffer.Remove(aEntry);
         }
     }
 
-    NS_WARN_IF_FALSE(mCount == 0, "AddPurpleRoot failed");
+private:
+    GCGraphBuilder &mBuilder;
+};
+
+void
+nsPurpleBuffer::SelectPointers(GCGraphBuilder &aBuilder)
+{
+    SelectPointersVisitor visitor(aBuilder);
+    VisitEntries(visitor);
+
+    MOZ_ASSERT(mCount == 0, "AddPurpleRoot failed");
     if (mCount == 0) {
         FreeBlocks();
         InitBlocks();
@@ -2120,31 +2144,38 @@ MayHaveChild(void *o, nsCycleCollectionParticipant* cp)
     return cf.MayHaveChild();
 }
 
+class RemoveSkippableVisitor
+{
+public:
+    RemoveSkippableVisitor(bool aRemoveChildlessNodes)
+        : mRemoveChildlessNodes(aRemoveChildlessNodes)
+    {}
+
+    void
+    Visit(nsPurpleBuffer &aBuffer, nsPurpleBufferEntry *aEntry)
+    {
+        if (aEntry->mObject) {
+            void *o = aEntry->mObject;
+            nsCycleCollectionParticipant *cp = aEntry->mParticipant;
+            CanonicalizeParticipant(&o, &cp);
+            if (!aEntry->mNotPurple && !cp->CanSkip(o, false) &&
+                (!mRemoveChildlessNodes || MayHaveChild(o, cp))) {
+                return;
+            }
+            cp->UnmarkIfPurple(o);
+        }
+        aBuffer.Remove(aEntry);
+    }
+
+private:
+    bool mRemoveChildlessNodes;
+};
+
 void
 nsPurpleBuffer::RemoveSkippable(bool removeChildlessNodes)
 {
-    // Walk through all the blocks.
-    for (Block *b = &mFirstBlock; b; b = b->mNext) {
-        for (nsPurpleBufferEntry *e = b->mEntries,
-                              *eEnd = ArrayEnd(b->mEntries);
-            e != eEnd; ++e) {
-            if (!(uintptr_t(e->mObject) & uintptr_t(1))) {
-                // This is a real entry (rather than something on the
-                // free list).
-                if (e->mObject) {
-                    void *o = e->mObject;
-                    nsCycleCollectionParticipant *cp = e->mParticipant;
-                    CanonicalizeParticipant(&o, &cp);
-                    if (!e->mNotPurple && !cp->CanSkip(o, false) &&
-                        (!removeChildlessNodes || MayHaveChild(o, cp))) {
-                        continue;
-                    }
-                    cp->UnmarkIfPurple(o);
-                }
-                Remove(e);
-            }
-        }
-    }
+    RemoveSkippableVisitor visitor(removeChildlessNodes);
+    VisitEntries(visitor);
 }
 
 void