From eddc75fd8f35b90c616db3d074405353aa9a4a0d Mon Sep 17 00:00:00 2001
From: Jon Coppeard <jcoppeard@mozilla.com>
Date: Wed, 22 Jan 2014 11:28:06 +0000
Subject: [PATCH] Bug 961077 - Make PersistentRooted use private inheritance
 when deriving from LinkedListElement r=sfink

---
 js/public/RootingAPI.h    |  9 +++---
 js/src/gc/RootMarking.cpp | 61 ++++++++++++++++++++++++---------------
 2 files changed, 43 insertions(+), 27 deletions(-)

diff --git a/js/public/RootingAPI.h b/js/public/RootingAPI.h
index 9f448d3018c2..2df52442a5f2 100644
--- a/js/public/RootingAPI.h
+++ b/js/public/RootingAPI.h
@@ -138,6 +138,7 @@ struct NullPtr
 
 namespace gc {
 struct Cell;
+struct PersistentRootedMarker;
 } /* namespace gc */
 
 } /* namespace js */
@@ -1098,7 +1099,6 @@ MutableHandle<T>::MutableHandle(PersistentRooted<T> *root)
     ptr = root->address();
 }
 
-
 /*
  * A copyable, assignable global GC root type with arbitrary lifetime, an
  * infallible constructor, and automatic unrooting on destruction.
@@ -1132,9 +1132,10 @@ MutableHandle<T>::MutableHandle(PersistentRooted<T> *root)
  * marked when the object itself is marked.
  */
 template<typename T>
-class PersistentRooted : public mozilla::LinkedListElement<PersistentRooted<T> > {
-    typedef mozilla::LinkedList<PersistentRooted> List;
-    typedef mozilla::LinkedListElement<PersistentRooted> Element;
+class PersistentRooted : private mozilla::LinkedListElement<PersistentRooted<T> > {
+    friend class mozilla::LinkedList<PersistentRooted>;
+    friend class mozilla::LinkedListElement<PersistentRooted>;
+    friend class js::gc::PersistentRootedMarker;
 
     void registerWithRuntime(JSRuntime *rt) {
         JS::shadow::Runtime *srt = JS::shadow::Runtime::asShadowRuntime(rt);
diff --git a/js/src/gc/RootMarking.cpp b/js/src/gc/RootMarking.cpp
index cfb039c332a5..a8016d44ed7e 100644
--- a/js/src/gc/RootMarking.cpp
+++ b/js/src/gc/RootMarking.cpp
@@ -618,21 +618,35 @@ JSPropertyDescriptor::trace(JSTracer *trc)
     }
 }
 
-// Mark a chain of PersistentRooted pointers that might be null.
-template<typename Referent>
-static void
-MarkPersistentRootedChain(JSTracer *trc,
-                          mozilla::LinkedList<PersistentRooted<Referent *> > &list,
-                          void (*marker)(JSTracer *trc, Referent **ref, const char *name),
-                          const char *name)
+namespace js {
+namespace gc {
+struct PersistentRootedMarker
 {
-    for (PersistentRooted<Referent *> *r = list.getFirst();
-         r != nullptr;
-         r = r->getNext())
+    template<typename Referent>
+    static void
+    markChainIfNotNull(JSTracer *trc,
+                       mozilla::LinkedList<PersistentRooted<Referent *> > &list,
+                       void (*marker)(JSTracer *trc, Referent **ref, const char *name),
+                       const char *name)
     {
-        if (r->get())
+        for (PersistentRooted<Referent *> *r = list.getFirst(); r; r = r->getNext()) {
+            if (r->get())
+                marker(trc, r->address(), name);
+        }
+    }
+
+    template<typename Referent>
+    static void
+    markChain(JSTracer *trc,
+              mozilla::LinkedList<PersistentRooted<Referent> > &list,
+              void (*marker)(JSTracer *trc, Referent *ref, const char *name),
+              const char *name)
+    {
+        for (PersistentRooted<Referent> *r = list.getFirst(); r; r = r->getNext())
             marker(trc, r->address(), name);
     }
+};
+}
 }
 
 void
@@ -640,20 +654,21 @@ js::gc::MarkPersistentRootedChains(JSTracer *trc)
 {
     JSRuntime *rt = trc->runtime;
 
-    MarkPersistentRootedChain(trc, rt->functionPersistentRooteds, &MarkObjectRoot,
-                              "PersistentRooted<JSFunction *>");
-    MarkPersistentRootedChain(trc, rt->objectPersistentRooteds, &MarkObjectRoot,
-                              "PersistentRooted<JSObject *>");
-    MarkPersistentRootedChain(trc, rt->scriptPersistentRooteds, &MarkScriptRoot,
-                              "PersistentRooted<JSScript *>");
-    MarkPersistentRootedChain(trc, rt->stringPersistentRooteds, &MarkStringRoot, 
-                              "PersistentRooted<JSString *>");
+    // Mark the PersistentRooted chains of types that may be null.
+    PersistentRootedMarker::markChainIfNotNull(trc, rt->functionPersistentRooteds, &MarkObjectRoot,
+                                               "PersistentRooted<JSFunction *>");
+    PersistentRootedMarker::markChainIfNotNull(trc, rt->objectPersistentRooteds, &MarkObjectRoot,
+                                               "PersistentRooted<JSObject *>");
+    PersistentRootedMarker::markChainIfNotNull(trc, rt->scriptPersistentRooteds, &MarkScriptRoot,
+                                               "PersistentRooted<JSScript *>");
+    PersistentRootedMarker::markChainIfNotNull(trc, rt->stringPersistentRooteds, &MarkStringRoot,
+                                               "PersistentRooted<JSString *>");
 
     // Mark the PersistentRooted chains of types that are never null.
-    for (JS::PersistentRootedId *r = rt->idPersistentRooteds.getFirst(); r != nullptr; r = r->getNext())
-        MarkIdRoot(trc, r->address(), "PersistentRooted<jsid>");
-    for (JS::PersistentRootedValue *r = rt->valuePersistentRooteds.getFirst(); r != nullptr; r = r->getNext())
-        MarkValueRoot(trc, r->address(), "PersistentRooted<Value>");
+    PersistentRootedMarker::markChain(trc, rt->idPersistentRooteds, &MarkIdRoot,
+                                      "PersistentRooted<jsid>");
+    PersistentRootedMarker::markChain(trc, rt->valuePersistentRooteds, &MarkValueRoot,
+                                      "PersistentRooted<Value>");
 }
 
 void