Bug 681104 - Add JSTracer flag to disable visiting WeakMap mappings. r=billm

js/src/jsapi.h

@@ -1659,6 +1659,10 @@ JSVAL_TRACE_KIND(jsval v)
  * internal implementation-specific traversal kind. In the latter case the only
  * operations on thing that the callback can do is to call JS_TraceChildren or
  * DEBUG-only JS_PrintTraceThingInfo.
+ *
+ * If eagerlyTraceWeakMaps is true, when we trace a WeakMap visit all
+ * of its mappings.  This should be used in cases where the tracer
+ * wants to use the existing liveness of entries.
  */
 typedef void
 (* JSTraceCallback)(JSTracer *trc, void *thing, JSGCTraceKind kind);
@@ -1669,6 +1673,7 @@ struct JSTracer {
     JSTraceNamePrinter  debugPrinter;
     const void          *debugPrintArg;
     size_t              debugPrintIndex;
+    JSBool              eagerlyTraceWeakMaps;
 };
 
 /*
@@ -1768,6 +1773,7 @@ JS_CallTracer(JSTracer *trc, void *thing, JSGCTraceKind kind);
         (trc)->debugPrinter = NULL;                                           \
         (trc)->debugPrintArg = NULL;                                          \
         (trc)->debugPrintIndex = (size_t)-1;                                  \
+        (trc)->eagerlyTraceWeakMaps = JS_TRUE;                                \
     JS_END_MACRO
 
 extern JS_PUBLIC_API(void)

js/src/jsgc.cpp

@@ -1555,6 +1555,12 @@ GCMarker::GCMarker(JSContext *cx)
     conservativeDumpFileName = getenv("JS_DUMP_CONSERVATIVE_GC_ROOTS");
     memset(&conservativeStats, 0, sizeof(conservativeStats));
 #endif
+
+    /*
+     * The GC is recomputing the liveness of WeakMap entries, so we
+     * delay visting entries.
+     */
+    eagerlyTraceWeakMaps = JS_FALSE;
 }
 
 GCMarker::~GCMarker()
@@ -1579,7 +1585,7 @@ GCMarker::delayMarkingChildren(const void *thing)
 }
 
 static void
-MarkDelayedChildren(JSTracer *trc, Arena *a)
+MarkDelayedChildren(GCMarker *trc, Arena *a)
 {
     AllocKind allocKind = a->aheader.getAllocKind();
     JSGCTraceKind traceKind = MapAllocToTraceKind(allocKind);

js/src/jsweakmap.h

@@ -144,6 +144,7 @@ class WeakMapBase {
             // many keys as possible have been marked, and add ourselves to the list of
             // known-live WeakMaps to be scanned in the iterative marking phase, by
             // markAllIteratively.
+            JS_ASSERT(!tracer->eagerlyTraceWeakMaps);
             JSRuntime *rt = tracer->context->runtime;
             next = rt->gcWeakMapList;
             rt->gcWeakMapList = this;
@@ -152,7 +153,8 @@ class WeakMapBase {
             // nicely as needed by the true ephemeral marking algorithm --- custom tracers
             // must use their own means for cycle detection. So here we do a conservative
             // approximation: pretend all keys are live.
-            nonMarkingTrace(tracer);
+            if (tracer->eagerlyTraceWeakMaps)
+                nonMarkingTrace(tracer);
         }
     }
 

js/src/xpconnect/src/nsXPConnect.cpp

@@ -880,6 +880,10 @@ nsXPConnect::Traverse(void *p, nsCycleCollectionTraversalCallback &cb)
     TraversalTracer trc(cb);
 
     JS_TRACER_INIT(&trc, cx, NoteJSChild);
+    // When WeakMaps are properly integrated with the cycle
+    // collector in Bug 668855, don't eagerly trace weak maps when
+    // building the cycle collector graph.
+    // trc.eagerlyTraceWeakMaps = JS_FALSE;
     JS_TraceChildren(&trc, p, traceKind);
 
     if(traceKind != JSTRACE_OBJECT || dontTraverse)