bug 1397297, make SnowWhite freeing more incremental, r=smaug

--HG--
extra : rebase_source : 0772adabddb6cee33d83184d32c981d3920ea6e6

js/xpconnect/src/XPCJSRuntime.cpp

@@ -129,7 +129,10 @@ public:
       AUTO_PROFILER_LABEL("AsyncFreeSnowWhite::Run", GCCC);
 
       TimeStamp start = TimeStamp::Now();
-      bool hadSnowWhiteObjects = nsCycleCollector_doDeferredDeletion();
+      // 2 ms budget, given that kICCSliceBudget is only 3 ms
+      js::SliceBudget budget = js::SliceBudget(js::TimeBudget(2));
+      bool hadSnowWhiteObjects =
+        nsCycleCollector_doDeferredDeletionWithBudget(budget);
       Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR_ASYNC_SNOW_WHITE_FREEING,
                             uint32_t((TimeStamp::Now() - start).ToMilliseconds()));
       if (hadSnowWhiteObjects && !mContinuation) {
@@ -146,7 +149,7 @@ public:
   nsresult Dispatch()
   {
       nsCOMPtr<nsIRunnable> self(this);
-      return NS_IdleDispatchToCurrentThread(self.forget(), 2500);
+      return NS_IdleDispatchToCurrentThread(self.forget(), 500);
   }
 
   void Start(bool aContinuation = false, bool aPurge = false)

xpcom/base/nsCycleCollector.cpp

@@ -1353,6 +1353,7 @@ public:
   void ForgetSkippable(js::SliceBudget& aBudget, bool aRemoveChildlessNodes,
                        bool aAsyncSnowWhiteFreeing);
   bool FreeSnowWhite(bool aUntilNoSWInPurpleBuffer);
+  bool FreeSnowWhiteWithBudget(js::SliceBudget& aBudget);
 
   // This method assumes its argument is already canonicalized.
   void RemoveObjectFromGraph(void* aPtr);
@@ -2715,40 +2716,66 @@ class SnowWhiteKiller : public TraceCallbacks
     ObjectsVector;
 
 public:
-  explicit SnowWhiteKiller(nsCycleCollector* aCollector)
+  SnowWhiteKiller(nsCycleCollector* aCollector, js::SliceBudget* aBudget)
     : mCollector(aCollector)
     , mObjects(kSegmentSize)
+    , mBudget(aBudget)
+    , mSawSnowWhiteObjects(false)
   {
     MOZ_ASSERT(mCollector, "Calling SnowWhiteKiller after nsCC went away");
   }
 
+  explicit SnowWhiteKiller(nsCycleCollector* aCollector)
+    : SnowWhiteKiller(aCollector, nullptr)
+  {
+  }
+
   ~SnowWhiteKiller()
   {
     for (auto iter = mObjects.Iter(); !iter.Done(); iter.Next()) {
       SnowWhiteObject& o = iter.Get();
-      if (!o.mRefCnt->get() && !o.mRefCnt->IsInPurpleBuffer()) {
-        mCollector->RemoveObjectFromGraph(o.mPointer);
-        o.mRefCnt->stabilizeForDeletion();
-        {
-          JS::AutoEnterCycleCollection autocc(mCollector->Runtime()->Runtime());
-          o.mParticipant->Trace(o.mPointer, *this, nullptr);
-        }
-        o.mParticipant->DeleteCycleCollectable(o.mPointer);
+      MaybeKillObject(o);
+    }
+  }
+
+  void
+  MaybeKillObject(SnowWhiteObject& aObject)
+  {
+    if (!aObject.mRefCnt->get() && !aObject.mRefCnt->IsInPurpleBuffer()) {
+      mCollector->RemoveObjectFromGraph(aObject.mPointer);
+      aObject.mRefCnt->stabilizeForDeletion();
+      {
+        JS::AutoEnterCycleCollection autocc(mCollector->Runtime()->Runtime());
+        aObject.mParticipant->Trace(aObject.mPointer, *this, nullptr);
       }
+      aObject.mParticipant->DeleteCycleCollectable(aObject.mPointer);
     }
   }
 
   bool
   Visit(nsPurpleBuffer& aBuffer, nsPurpleBufferEntry* aEntry)
   {
+    if (mBudget) {
+      if (mBudget->isOverBudget()) {
+        return false;
+      }
+      mBudget->step();
+    }
+
     MOZ_ASSERT(aEntry->mObject, "Null object in purple buffer");
     if (!aEntry->mRefCnt->get()) {
+      mSawSnowWhiteObjects = true;
       void* o = aEntry->mObject;
       nsCycleCollectionParticipant* cp = aEntry->mParticipant;
       ToParticipant(o, &cp);
       SnowWhiteObject swo = { o, cp, aEntry->mRefCnt };
-      mObjects.InfallibleAppend(swo);
+      if (!mBudget) {
+        mObjects.InfallibleAppend(swo);
+      }
       aBuffer.Remove(aEntry);
+      if (mBudget) {
+        MaybeKillObject(swo);
+      }
     }
     return true;
   }
@@ -2758,6 +2785,11 @@ public:
     return !mObjects.IsEmpty();
   }
 
+  bool SawSnowWhiteObjects() const
+  {
+    return mSawSnowWhiteObjects;
+  }
+
   virtual void Trace(JS::Heap<JS::Value>* aValue, const char* aName,
                      void* aClosure) const override
   {
@@ -2817,6 +2849,8 @@ public:
 private:
   RefPtr<nsCycleCollector> mCollector;
   ObjectsVector mObjects;
+  js::SliceBudget* mBudget;
+  bool mSawSnowWhiteObjects;
 };
 
 class RemoveSkippableVisitor : public SnowWhiteKiller
@@ -2925,6 +2959,23 @@ nsCycleCollector::FreeSnowWhite(bool aUntilNoSWInPurpleBuffer)
   return hadSnowWhiteObjects;
 }
 
+bool
+nsCycleCollector::FreeSnowWhiteWithBudget(js::SliceBudget& aBudget)
+{
+  CheckThreadSafety();
+
+  if (mFreeingSnowWhite) {
+    return false;
+  }
+
+  AutoRestore<bool> ar(mFreeingSnowWhite);
+  mFreeingSnowWhite = true;
+
+  SnowWhiteKiller visitor(this, &aBudget);
+  mPurpleBuf.VisitEntries(visitor);
+  return visitor.SawSnowWhiteObjects();;
+}
+
 void
 nsCycleCollector::ForgetSkippable(js::SliceBudget& aBudget,
                                   bool aRemoveChildlessNodes,
@@ -4320,6 +4371,19 @@ nsCycleCollector_doDeferredDeletion()
   return data->mCollector->FreeSnowWhite(false);
 }
 
+bool
+nsCycleCollector_doDeferredDeletionWithBudget(js::SliceBudget& aBudget)
+{
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+  MOZ_ASSERT(data->mContext);
+
+  return data->mCollector->FreeSnowWhiteWithBudget(aBudget);
+}
+
 already_AddRefed<nsICycleCollectorLogSink>
 nsCycleCollector_createLogSink()
 {

xpcom/base/nsCycleCollector.h

@@ -43,6 +43,7 @@ void nsCycleCollector_finishAnyCurrentCollection();
 void nsCycleCollector_dispatchDeferredDeletion(bool aContinuation = false,
                                                bool aPurge = false);
 bool nsCycleCollector_doDeferredDeletion();
+bool nsCycleCollector_doDeferredDeletionWithBudget(js::SliceBudget& aBudget);
 
 already_AddRefed<nsICycleCollectorLogSink> nsCycleCollector_createLogSink();