Bug 720686, add some cycle collection optimizations to XPC, f=mrbkap,r=mccr8

--HG--
extra : rebase_source : 7e8f68a30048f613acc99201c3c1e12b6f74eaba

js/xpconnect/src/XPCJSRuntime.cpp

@@ -56,7 +56,7 @@
 #include "mozilla/Telemetry.h"
 
 #include "nsContentUtils.h"
-
+#include "nsCCUncollectableMarker.h"
 #include "jsfriendapi.h"
 #include "js/MemoryMetrics.h"
 
@@ -573,12 +573,30 @@ XPCJSRuntime::AddXPConnectRoots(JSContext* cx,
 
     XPCWrappedNativeScope::SuspectAllWrappers(this, cx, cb);
 
-    for (XPCRootSetElem *e = mVariantRoots; e ; e = e->GetNextRoot())
-        cb.NoteXPCOMRoot(static_cast<XPCTraceableVariant*>(e));
+    for (XPCRootSetElem *e = mVariantRoots; e ; e = e->GetNextRoot()) {
+        XPCTraceableVariant* v = static_cast<XPCTraceableVariant*>(e);
+        if (nsCCUncollectableMarker::InGeneration(cb,
+                                                  v->CCGeneration())) {
+           jsval val = v->GetJSValPreserveColor();
+           if (val.isObject() && !xpc_IsGrayGCThing(&val.toObject()))
+               continue;
+        }
+        cb.NoteXPCOMRoot(v);
+    }
 
     for (XPCRootSetElem *e = mWrappedJSRoots; e ; e = e->GetNextRoot()) {
         nsXPCWrappedJS *wrappedJS = static_cast<nsXPCWrappedJS*>(e);
         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.
+        if (nsCCUncollectableMarker::sGeneration &&
+            !cb.WantAllTraces() && (!obj || !xpc_IsGrayGCThing(obj)) &&
+            !wrappedJS->IsSubjectToFinalization() &&
+            wrappedJS->GetRootWrapper() == wrappedJS &&
+            !wrappedJS->IsAggregatedToNative()) {
+            continue;
+        }
 
         // Only suspect wrappedJSObjects that are in a compartment that
         // participates in cycle collection.

js/xpconnect/src/XPCVariant.cpp

@@ -60,7 +60,7 @@ NS_IMPL_CYCLE_COLLECTING_ADDREF(XPCVariant)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(XPCVariant)
 
 XPCVariant::XPCVariant(XPCCallContext& ccx, jsval aJSVal)
-    : mJSVal(aJSVal)
+    : mJSVal(aJSVal), mCCGeneration(0)
 {
     nsVariant::Initialize(&mData);
     if (!JSVAL_IS_PRIMITIVE(mJSVal)) {

js/xpconnect/src/nsXPConnect.cpp

@@ -823,6 +823,30 @@ NoteJSChild(JSTracer *trc, void *thing, JSGCTraceKind kind)
     }
 }
 
+void
+xpc_MarkInCCGeneration(nsISupports* aVariant, PRUint32 aGeneration)
+{
+    nsCOMPtr<XPCVariant> variant = do_QueryInterface(aVariant);
+    if (variant) {
+        variant->SetCCGeneration(aGeneration);
+        variant->GetJSVal(); // Unmarks gray JSObject.
+        XPCVariant* weak = variant.get();
+        variant = nsnull;
+        if (weak->IsPurple()) {
+          weak->RemovePurple();
+        }
+    }
+}
+
+void
+xpc_UnmarkGrayObject(nsIXPConnectWrappedJS* aWrappedJS)
+{
+    if (aWrappedJS) {
+        // Unmarks gray JSObject.
+        static_cast<nsXPCWrappedJS*>(aWrappedJS)->GetJSObject();
+    }
+}
+
 static JSBool
 WrapperIsNotMainThreadOnly(XPCWrappedNative *wrapper)
 {

js/xpconnect/src/xpcprivate.h

@@ -4279,6 +4279,22 @@ public:
                                   nsIVariant* variant,
                                   nsresult* pErr, jsval* pJSVal);
 
+    bool IsPurple()
+    {
+        return mRefCnt.IsPurple();
+    }
+
+    void RemovePurple()
+    {
+        mRefCnt.RemovePurple();
+    }
+
+    void SetCCGeneration(PRUint32 aGen)
+    {
+        mCCGeneration = aGen;
+    }
+
+    PRUint32 CCGeneration() { return mCCGeneration; }
 protected:
     virtual ~XPCVariant() { }
 
@@ -4287,7 +4303,8 @@ protected:
 protected:
     nsDiscriminatedUnion mData;
     jsval                mJSVal;
-    JSBool               mReturnRawObject;
+    bool                 mReturnRawObject : 1;
+    PRUint32             mCCGeneration : 31;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(XPCVariant, XPCVARIANT_IID)

js/xpconnect/src/xpcpublic.h

@@ -55,6 +55,7 @@
 #include "nsTArray.h"
 
 class nsIPrincipal;
+class nsIXPConnectWrappedJS;
 struct nsDOMClassInfoData;
 
 #ifndef BAD_TLS_INDEX
@@ -189,6 +190,15 @@ xpc_UnmarkGrayObject(JSObject *obj)
         xpc_UnmarkGrayObjectRecursive(obj);
 }
 
+// If aVariant is an XPCVariant, this marks the object to be in aGeneration.
+// This also unmarks the gray JSObject.
+extern void
+xpc_MarkInCCGeneration(nsISupports* aVariant, PRUint32 aGeneration);
+
+// Unmarks aWrappedJS's JSObject.
+extern void
+xpc_UnmarkGrayObject(nsIXPConnectWrappedJS* aWrappedJS);
+
 // No JS can be on the stack when this is called. Probably only useful from
 // xpcshell.
 NS_EXPORT_(void)