Backed out changeset 300f5b7d72e1 (bug 897433) for intermittent Linux dromaeo crashes.

dom/base/nsJSEnvironment.cpp

@@ -135,8 +135,6 @@ static PRLogModuleInfo* gJSDiagnostics;
 // Large value used to specify that a script should run essentially forever
 #define NS_UNLIMITED_SCRIPT_RUNTIME (0x40000000LL << 32)
 
-#define NS_MAJOR_FORGET_SKIPPABLE_CALLS 2
-
 // if you add statics here, add them to the list in nsJSRuntime::Startup
 
 static nsITimer *sGCTimer;
@@ -2504,9 +2502,7 @@ FireForgetSkippable(uint32_t aSuspected, bool aRemoveChildless)
 {
   PRTime startTime = PR_Now();
   FinishAnyIncrementalGC();
-  bool earlyForgetSkippable =
-    sCleanupsSinceLastGC < NS_MAJOR_FORGET_SKIPPABLE_CALLS;
-  nsCycleCollector_forgetSkippable(aRemoveChildless, earlyForgetSkippable);
+  nsCycleCollector_forgetSkippable(aRemoveChildless);
   sPreviousSuspectedCount = nsCycleCollector_suspectedCount();
   ++sCleanupsSinceLastGC;
   PRTime delta = PR_Now() - startTime;
@@ -2556,9 +2552,8 @@ nsJSContext::CycleCollectNow(nsICycleCollectorListener *aListener,
 
   // Run forgetSkippable synchronously to reduce the size of the CC graph. This
   // is particularly useful if we recently finished a GC.
-  if (sCleanupsSinceLastGC < NS_MAJOR_FORGET_SKIPPABLE_CALLS &&
-      aExtraForgetSkippableCalls >= 0) {
-    while (sCleanupsSinceLastGC < NS_MAJOR_FORGET_SKIPPABLE_CALLS) {
+  if (sCleanupsSinceLastGC < 2 && aExtraForgetSkippableCalls >= 0) {
+    while (sCleanupsSinceLastGC < 2) {
       FireForgetSkippable(nsCycleCollector_suspectedCount(), false);
       ranSyncForgetSkippable = true;
     }

toolkit/components/telemetry/Histograms.json

@@ -86,12 +86,6 @@
     "kind": "flag",
     "description": "Set if the cycle collector ran out of memory at some point"
   },
-  "CYCLE_COLLECTOR_ASYNC_SNOW_WHITE_FREEING": {
-    "kind": "exponential",
-    "high": "10000",
-    "n_buckets": 50,
-    "description": "Time spent on one asynchronous SnowWhite freeing (ms)"
-  },
   "FORGET_SKIPPABLE_MAX": {
     "kind": "exponential",
     "high": "10000",

xpcom/base/nsCycleCollector.cpp

@@ -775,15 +775,14 @@ public:
 
     void SelectPointers(GCGraphBuilder &builder);
 
-    // RemoveSkippable removes entries from the purple buffer synchronously
-    // (1) if aAsyncSnowWhiteFreeing is false and nsPurpleBufferEntry::mRefCnt is 0 or
-    // (2) if the object's nsXPCOMCycleCollectionParticipant::CanSkip() returns true or
-    // (3) if nsPurpleBufferEntry::mRefCnt->IsPurple() is false.
-    // (4) If removeChildlessNodes is true, then any nodes in the purple buffer
-    //     that will have no children in the cycle collector graph will also be
-    //     removed. CanSkip() may be run on these children.
+    // RemoveSkippable removes entries from the purple buffer if
+    // nsPurpleBufferEntry::mRefCnt is 0 or if the object's
+    // nsXPCOMCycleCollectionParticipant::CanSkip() returns true or
+    // if nsPurpleBufferEntry::mRefCnt->IsPurple() is false.
+    // If removeChildlessNodes is true, then any nodes in the purple buffer
+    // that will have no children in the cycle collector graph will also be
+    // removed. CanSkip() may be run on these children.
     void RemoveSkippable(bool removeChildlessNodes,
-                         bool aAsyncSnowWhiteFreeing,
                          CC_ForgetSkippableCallback aCb);
 
     nsPurpleBufferEntry* NewEntry()
@@ -1038,7 +1037,7 @@ public:
     void ScanRoots();
     void ScanWeakMaps();
 
-    void ForgetSkippable(bool aRemoveChildlessNodes, bool aAsyncSnowWhiteFreeing);
+    void ForgetSkippable(bool removeChildlessNodes);
 
     // returns whether anything was collected
     bool CollectWhite(nsICycleCollectorListener *aListener);
@@ -1073,12 +1072,11 @@ public:
     bool BeginCollection(ccType aCCType, nsICycleCollectorListener *aListener);
     bool FinishCollection(nsICycleCollectorListener *aListener);
 
-    bool FreeSnowWhite(bool aUntilNoSWInPurpleBuffer);
+    void FreeSnowWhite(bool aUntilNoSWInPurpleBuffer);
 
     // If there is a cycle collector available in the current thread,
-    // this calls FreeSnowWhite(false). Returns true if some
-    // snow-white objects were found.
-    static bool TryToFreeSnowWhite();
+    // this calls FreeSnowWhite(false).
+    static void TryToFreeSnowWhite();
 
     uint32_t SuspectedCount();
     void Shutdown();
@@ -2150,33 +2148,6 @@ MayHaveChild(void *o, nsCycleCollectionParticipant* cp)
     return cf.MayHaveChild();
 }
 
-class AsyncFreeSnowWhite : public nsRunnable
-{
-public:
-  NS_IMETHOD Run()
-  {
-      PRTime start = PR_Now();
-      bool hadSnowWhiteObjects = nsCycleCollector::TryToFreeSnowWhite();
-      Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR_ASYNC_SNOW_WHITE_FREEING,
-                            uint32_t(PR_Now() - start) / PR_USEC_PER_MSEC);
-      if (hadSnowWhiteObjects && !mContinuation) {
-          mContinuation = true;
-          NS_DispatchToCurrentThread(this);
-      }
-      return NS_OK;
-  }
-
-  static void Dispatch(bool aContinuation = false)
-  {
-      nsRefPtr<AsyncFreeSnowWhite> ev = new AsyncFreeSnowWhite(aContinuation);
-      NS_DispatchToCurrentThread(ev);
-  }
-private:
-  AsyncFreeSnowWhite(bool aContinuation) : mContinuation(aContinuation) {}
-
-  bool mContinuation;
-};
-
 struct SnowWhiteObject
 {
   void* mPointer;
@@ -2238,12 +2209,9 @@ class RemoveSkippableVisitor : public SnowWhiteKiller
 {
 public:
     RemoveSkippableVisitor(uint32_t aMaxCount, bool aRemoveChildlessNodes,
-                           bool aAsyncSnowWhiteFreeing,
                            CC_ForgetSkippableCallback aCb)
-        : SnowWhiteKiller(aAsyncSnowWhiteFreeing ? 0 : aMaxCount),
+        : SnowWhiteKiller(aMaxCount),
           mRemoveChildlessNodes(aRemoveChildlessNodes),
-          mAsyncSnowWhiteFreeing(aAsyncSnowWhiteFreeing),
-          mDispatchedDeferredDeletion(false),
           mCallback(aCb)
     {}
 
@@ -2254,10 +2222,6 @@ public:
         if (mCallback) {
             mCallback();
         }
-        if (HasSnowWhiteObjects()) {
-            // Effectively a continuation.
-            AsyncFreeSnowWhite::Dispatch(true);
-        }
     }
 
     void
@@ -2265,12 +2229,7 @@ public:
     {
         MOZ_ASSERT(aEntry->mObject, "null mObject in purple buffer");
         if (!aEntry->mRefCnt->get()) {
-            if (!mAsyncSnowWhiteFreeing) {
-                SnowWhiteKiller::Visit(aBuffer, aEntry);
-            } else if (!mDispatchedDeferredDeletion) {
-                mDispatchedDeferredDeletion = true;
-                nsCycleCollector_dispatchDeferredDeletion();
-            }
+            SnowWhiteKiller::Visit(aBuffer, aEntry);
             return;
         }
         void *o = aEntry->mObject;
@@ -2285,44 +2244,57 @@ public:
 
 private:
     bool mRemoveChildlessNodes;
-    bool mAsyncSnowWhiteFreeing;
-    bool mDispatchedDeferredDeletion;
     CC_ForgetSkippableCallback mCallback;
 };
 
 void
-nsPurpleBuffer::RemoveSkippable(bool aRemoveChildlessNodes,
-                                bool aAsyncSnowWhiteFreeing,
+nsPurpleBuffer::RemoveSkippable(bool removeChildlessNodes,
                                 CC_ForgetSkippableCallback aCb)
 {
-    RemoveSkippableVisitor visitor(Count(), aRemoveChildlessNodes,
-                                   aAsyncSnowWhiteFreeing, aCb);
+    RemoveSkippableVisitor visitor(Count(), removeChildlessNodes, aCb);
     VisitEntries(visitor);
+    // If we're about to delete some objects when visitor goes out of scope,
+    // try to delete some more soon.
+    if (visitor.HasSnowWhiteObjects()) {
+        nsCycleCollector_dispatchDeferredDeletion();
+    }
 }
 
-bool
+class AsyncFreeSnowWhite : public nsRunnable
+{
+public:
+  NS_IMETHOD Run()
+  {
+      nsCycleCollector::TryToFreeSnowWhite();
+      return NS_OK;
+  }
+
+  static void Dispatch()
+  {
+      nsRefPtr<AsyncFreeSnowWhite> ev = new AsyncFreeSnowWhite();
+      NS_DispatchToCurrentThread(ev);
+  }
+};
+
+void
 nsCycleCollector::FreeSnowWhite(bool aUntilNoSWInPurpleBuffer)
 {
-    bool hadSnowWhiteObjects = false;
     do {
         SnowWhiteKiller visitor(mPurpleBuf.Count());
         mPurpleBuf.VisitEntries(visitor);
-        hadSnowWhiteObjects = hadSnowWhiteObjects ||
-                              visitor.HasSnowWhiteObjects();
         if (!visitor.HasSnowWhiteObjects()) {
             break;
         }
     } while (aUntilNoSWInPurpleBuffer);
-    return hadSnowWhiteObjects;
 }
 
-/* static */ bool
+/* static */ void
 nsCycleCollector::TryToFreeSnowWhite()
 {
   CollectorData* data = sCollectorData.get();
-  return data->mCollector ?
-      data->mCollector->FreeSnowWhite(false) :
-      false;
+  if (data->mCollector) {
+      data->mCollector->FreeSnowWhite(false);
+  }
 }
 
 void
@@ -2332,14 +2304,12 @@ nsCycleCollector::SelectPurple(GCGraphBuilder &builder)
 }
 
 void
-nsCycleCollector::ForgetSkippable(bool aRemoveChildlessNodes,
-                                  bool aAsyncSnowWhiteFreeing)
+nsCycleCollector::ForgetSkippable(bool removeChildlessNodes)
 {
     if (mJSRuntime) {
         mJSRuntime->PrepareForForgetSkippable();
     }
-    mPurpleBuf.RemoveSkippable(aRemoveChildlessNodes, aAsyncSnowWhiteFreeing,
-                               mForgetSkippableCB);
+    mPurpleBuf.RemoveSkippable(removeChildlessNodes, mForgetSkippableCB);
 }
 
 MOZ_NEVER_INLINE void
@@ -3287,8 +3257,7 @@ nsCycleCollector_setForgetSkippableCallback(CC_ForgetSkippableCallback aCB)
 }
 
 void
-nsCycleCollector_forgetSkippable(bool aRemoveChildlessNodes,
-                                 bool aAsyncSnowWhiteFreeing)
+nsCycleCollector_forgetSkippable(bool aRemoveChildlessNodes)
 {
     CollectorData *data = sCollectorData.get();
 
@@ -3298,8 +3267,7 @@ nsCycleCollector_forgetSkippable(bool aRemoveChildlessNodes,
 
     PROFILER_LABEL("CC", "nsCycleCollector_forgetSkippable");
     TimeLog timeLog;
-    data->mCollector->ForgetSkippable(aRemoveChildlessNodes,
-                                      aAsyncSnowWhiteFreeing);
+    data->mCollector->ForgetSkippable(aRemoveChildlessNodes);
     timeLog.Checkpoint("ForgetSkippable()");
 }
 

xpcom/base/nsCycleCollector.h

@@ -54,8 +54,7 @@ void nsCycleCollector_setBeforeUnlinkCallback(CC_BeforeUnlinkCallback aCB);
 typedef void (*CC_ForgetSkippableCallback)(void);
 void nsCycleCollector_setForgetSkippableCallback(CC_ForgetSkippableCallback aCB);
 
-void nsCycleCollector_forgetSkippable(bool aRemoveChildlessNodes = false,
-                                      bool aAsyncSnowWhiteFreeing = false);
+void nsCycleCollector_forgetSkippable(bool aRemoveChildlessNodes = false);
 
 void nsCycleCollector_dispatchDeferredDeletion();