Backed out changeset a9715a3b0e13 (bug 937818) for static rooting hazard analysis bustage on a CLOSED TREE

xpcom/base/nsCycleCollector.cpp

@@ -1178,8 +1178,7 @@ private:
 
     void BeginCollection(ccType aCCType, nsICycleCollectorListener *aManualListener);
     void MarkRoots(SliceBudget &aBudget);
-    void ScanRoots(bool aFullySynchGraphBuild);
-    void ScanIncrementalRoots();
+    void ScanRoots();
     void ScanWeakMaps();
 
     // returns whether anything was collected
@@ -2304,16 +2303,6 @@ nsCycleCollector::ForgetSkippable(bool aRemoveChildlessNodes,
                                   bool aAsyncSnowWhiteFreeing)
 {
     CheckThreadSafety();
-
-    // If we remove things from the purple buffer during graph building, we may
-    // lose track of an object that was mutated during graph building. This should
-    // only happen when somebody calls nsJSContext::CycleCollectNow explicitly
-    // requesting extra forget skippable calls, during an incremental collection.
-    // See bug 950949 for fixing this so we actually run the forgetSkippable calls.
-    if (mIncrementalPhase != IdlePhase) {
-        return;
-    }
-
     if (mJSRuntime) {
         mJSRuntime->PrepareForForgetSkippable();
     }
@@ -2485,138 +2474,28 @@ nsCycleCollector::ScanWeakMaps()
     }
 }
 
-// Flood black from any objects in the purple buffer that are in the CC graph.
-class PurpleScanBlackVisitor
-{
-public:
-    PurpleScanBlackVisitor(GCGraph &aGraph, uint32_t &aCount, bool &aFailed)
-        : mGraph(aGraph), mCount(aCount), mFailed(aFailed)
-    {
-    }
-
-    void
-    Visit(nsPurpleBuffer &aBuffer, nsPurpleBufferEntry *aEntry)
-    {
-        MOZ_ASSERT(aEntry->mObject, "Entries with null mObject shouldn't be in the purple buffer.");
-        MOZ_ASSERT(aEntry->mRefCnt->get() != 0, "Snow-white objects shouldn't be in the purple buffer.");
-
-        void *obj = aEntry->mObject;
-        if (!aEntry->mParticipant) {
-            obj = CanonicalizeXPCOMParticipant(static_cast<nsISupports*>(obj));
-            MOZ_ASSERT(obj, "Don't add objects that don't participate in collection!");
-        }
-
-        PtrInfo *pi = mGraph.FindNode(obj);
-        if (!pi) {
-            return;
-        }
-        MOZ_ASSERT(pi->mParticipant, "No dead objects should be in the purple buffer.");
-        if (pi->mColor == black) {
-            return;
-        }
-        GraphWalker<ScanBlackVisitor>(ScanBlackVisitor(mCount, mFailed)).Walk(pi);
-    }
-
-private:
-    GCGraph &mGraph;
-    uint32_t &mCount;
-    bool &mFailed;
-};
-
-// Objects that have been stored somewhere since the start of incremental graph building must
-// be treated as live for this cycle collection, because we may not have accurate information
-// about who holds references to them.
 void
-nsCycleCollector::ScanIncrementalRoots()
+nsCycleCollector::ScanRoots()
 {
     TimeLog timeLog;
-
-    // Reference counted objects:
-    // We cleared the purple buffer at the start of the current ICC, so if a
-    // refcounted object is purple, it may have been AddRef'd during the current
-    // ICC. (It may also have only been released.) If that is the case, we cannot
-    // be sure that the set of things pointing to the object in the CC graph
-    // is accurate. Therefore, for safety, we treat any purple objects as being
-    // live during the current CC. We don't remove anything from the purple
-    // buffer here, so these objects will be suspected and freed in the next CC
-    // if they are garbage.
-    bool failed = false;
-    PurpleScanBlackVisitor purpleScanBlackVisitor(mGraph, mWhiteNodeCount, failed);
-    mPurpleBuf.VisitEntries(purpleScanBlackVisitor);
-    timeLog.Checkpoint("ScanIncrementalRoots::fix purple");
-
-    // Garbage collected objects:
-    // If a GCed object was added to the graph with a refcount of zero, and is
-    // now marked black by the GC, it was probably gray before and was exposed
-    // to active JS, so it may have been stored somewhere, so it needs to be
-    // treated as live.
-    if (mJSRuntime) {
-        nsCycleCollectionParticipant *jsParticipant = mJSRuntime->GCThingParticipant();
-        nsCycleCollectionParticipant *zoneParticipant = mJSRuntime->ZoneParticipant();
-        NodePool::Enumerator etor(mGraph.mNodes);
-
-        while (!etor.IsDone()) {
-            PtrInfo *pi = etor.GetNext();
-
-            if (pi->mRefCount != 0 || pi->mColor == black) {
-                continue;
-            }
-
-            if (pi->mParticipant == jsParticipant) {
-                if (xpc_GCThingIsGrayCCThing(pi->mPointer)) {
-                    continue;
-                }
-            } else if (pi->mParticipant == zoneParticipant) {
-                JS::Zone *zone = static_cast<JS::Zone*>(pi->mPointer);
-                if (js::ZoneGlobalsAreAllGray(zone)) {
-                    continue;
-                }
-            } else {
-                MOZ_ASSERT(false, "Non-JS thing with 0 refcount? Treating as live.");
-            }
-
-            GraphWalker<ScanBlackVisitor>(ScanBlackVisitor(mWhiteNodeCount, failed)).Walk(pi);
-        }
-
-        timeLog.Checkpoint("ScanIncrementalRoots::fix JS");
-    }
-
-    if (failed) {
-        NS_ASSERTION(false, "Ran out of memory in ScanIncrementalRoots");
-        CC_TELEMETRY(_OOM, true);
-    }
-}
-
-void
-nsCycleCollector::ScanRoots(bool aFullySynchGraphBuild)
-{
     AutoRestore<bool> ar(mScanInProgress);
     MOZ_ASSERT(!mScanInProgress);
     mScanInProgress = true;
     mWhiteNodeCount = 0;
     MOZ_ASSERT(mIncrementalPhase == ScanAndCollectWhitePhase);
 
-    if (!aFullySynchGraphBuild) {
-        ScanIncrementalRoots();
-    }
-
-    TimeLog timeLog;
-
     // On the assumption that most nodes will be black, it's
     // probably faster to use a GraphWalker than a
     // NodePool::Enumerator.
     bool failed = false;
     GraphWalker<scanVisitor>(scanVisitor(mWhiteNodeCount, failed)).WalkFromRoots(mGraph);
-    timeLog.Checkpoint("ScanRoots::WalkFromRoots");
 
     if (failed) {
         NS_ASSERTION(false, "Ran out of memory in ScanRoots");
         CC_TELEMETRY(_OOM, true);
     }
 
-    // Scanning weak maps must be done last.
     ScanWeakMaps();
-    timeLog.Checkpoint("ScanRoots::ScanWeakMaps");
 
     if (mListener) {
         mListener->BeginResults();
@@ -2647,8 +2526,9 @@ nsCycleCollector::ScanRoots(bool aFullySynchGraphBuild)
 
         mListener->End();
         mListener = nullptr;
-        timeLog.Checkpoint("ScanRoots::listener");
     }
+
+    timeLog.Checkpoint("ScanRoots()");
 }
 
 
@@ -3011,7 +2891,7 @@ nsCycleCollector::Collect(ccType aCCType,
             // promoted to a strong reference after ScanRoots has finished.
             // See bug 926533.
             PrintPhase("ScanRoots");
-            ScanRoots(startedIdle);
+            ScanRoots();
             PrintPhase("CollectWhite");
             collectedAny = CollectWhite();
             break;