Bug 944492, part 2 - Make XPCWrappedJS a proper skippable class. r=smaug

js/xpconnect/src/XPCJSRuntime.cpp

@@ -668,35 +668,6 @@ XPCJSRuntime::SuspectWrappedNative(XPCWrappedNative *wrapper,
         cb.NoteJSRoot(obj);
 }
 
-bool
-CanSkipWrappedJS(nsXPCWrappedJS *wrappedJS)
-{
-    JSObject *obj = wrappedJS->GetJSObjectPreserveColor();
-    // If traversing wrappedJS wouldn't release it, nor
-    // cause any other objects to be added to the graph, no
-    // need to add it to the graph at all.
-    bool isRootWrappedJS = wrappedJS->IsRootWrapper();
-    if (nsCCUncollectableMarker::sGeneration &&
-        (!obj || !xpc_IsGrayGCThing(obj)) &&
-        !wrappedJS->IsSubjectToFinalization() &&
-        (isRootWrappedJS || CanSkipWrappedJS(wrappedJS->GetRootWrapper()))) {
-        if (!wrappedJS->IsAggregatedToNative() || !isRootWrappedJS) {
-            return true;
-        } else {
-            nsISupports* agg = wrappedJS->GetAggregatedNativeObject();
-            nsXPCOMCycleCollectionParticipant* cp = nullptr;
-            CallQueryInterface(agg, &cp);
-            nsISupports* canonical = nullptr;
-            agg->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
-                                reinterpret_cast<void**>(&canonical));
-            if (cp && canonical && cp->CanSkipInCC(canonical)) {
-                return true;
-            }
-        }
-    }
-    return false;
-}
-
 void
 XPCJSRuntime::TraverseAdditionalNativeRoots(nsCycleCollectionNoteRootCallback &cb)
 {
@@ -714,13 +685,7 @@ XPCJSRuntime::TraverseAdditionalNativeRoots(nsCycleCollectionNoteRootCallback &c
     }
 
     for (XPCRootSetElem *e = mWrappedJSRoots; e ; e = e->GetNextRoot()) {
-        nsXPCWrappedJS *wrappedJS = static_cast<nsXPCWrappedJS*>(e);
-        if (!cb.WantAllTraces() &&
-            CanSkipWrappedJS(wrappedJS)) {
-            continue;
-        }
-
-        cb.NoteXPCOMRoot(static_cast<nsIXPConnectWrappedJS *>(wrappedJS));
+        cb.NoteXPCOMRoot(ToSupports(static_cast<nsXPCWrappedJS*>(e)));
     }
 }
 

js/xpconnect/src/XPCWrappedJS.cpp

@@ -8,6 +8,7 @@
 
 #include "xpcprivate.h"
 #include "jsprf.h"
+#include "nsCCUncollectableMarker.h"
 #include "nsCxPusher.h"
 #include "nsContentUtils.h"
 #include "nsThreadUtils.h"
@@ -50,6 +51,42 @@ using namespace mozilla;
 // result in a leak if a wrapper in the non-rooting state has an aggregated native that
 // keeps alive the wrapper's JS object.  See bug 947049.
 
+
+// If traversing wrappedJS wouldn't release it, nor cause any other objects to be
+// added to the graph, there is no need to add it to the graph at all.
+bool
+nsXPCWrappedJS::CanSkip()
+{
+    if (!nsCCUncollectableMarker::sGeneration)
+        return false;
+
+    if (IsSubjectToFinalization())
+        return true;
+
+    // If this wrapper holds a gray object, need to trace it.
+    JSObject *obj = GetJSObjectPreserveColor();
+    if (obj && xpc_IsGrayGCThing(obj))
+        return false;
+
+    // For non-root wrappers, check if the root wrapper will be
+    // added to the CC graph.
+    if (!IsRootWrapper())
+        return mRoot->CanSkip();
+
+    // For the root wrapper, check if there is an aggregated
+    // native object that will be added to the CC graph.
+    if (!IsAggregatedToNative())
+        return true;
+
+    nsISupports* agg = GetAggregatedNativeObject();
+    nsXPCOMCycleCollectionParticipant* cp = nullptr;
+    CallQueryInterface(agg, &cp);
+    nsISupports* canonical = nullptr;
+    agg->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
+                        reinterpret_cast<void**>(&canonical));
+    return cp && canonical && cp->CanSkipThis(canonical);
+}
+
 NS_IMETHODIMP
 NS_CYCLE_COLLECTION_CLASSNAME(nsXPCWrappedJS)::Traverse
    (void *p, nsCycleCollectionTraversalCallback &cb)
@@ -103,6 +140,20 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsXPCWrappedJS)
     tmp->Unlink();
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
+// XPCJSRuntime keeps a table of WJS, so we can remove them from
+// the purple buffer in between CCs.
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(nsXPCWrappedJS)
+    return true;
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(nsXPCWrappedJS)
+    return tmp->CanSkip();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(nsXPCWrappedJS)
+    return tmp->CanSkip();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END
+
 NS_IMETHODIMP
 nsXPCWrappedJS::AggregatedQueryInterface(REFNSIID aIID, void** aInstancePtr)
 {

js/xpconnect/src/xpcprivate.h

@@ -2470,7 +2470,7 @@ public:
     NS_DECL_NSISUPPORTSWEAKREFERENCE
     NS_DECL_NSIPROPERTYBAG
 
-    NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(nsXPCWrappedJS, nsIXPConnectWrappedJS)
+    NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS_AMBIGUOUS(nsXPCWrappedJS, nsIXPConnectWrappedJS)
 
     NS_IMETHOD CallMethod(uint16_t methodIndex,
                           const XPTMethodDescriptor *info,
@@ -2533,6 +2533,7 @@ protected:
                    nsXPCWrappedJS* root,
                    nsISupports* aOuter);
 
+    bool CanSkip();
     void Destroy();
     void Unlink();