Bug 943839 - Simplify Anchor and get rid of JS_AnchorPtr. r=terrence

--HG--
extra : rebase_source : f2d9e039f758b6078c57f601537effe8c7c39f82

js/public/Anchor.h

@@ -93,14 +93,31 @@ class Anchor : AnchorPermitted<T>
     Anchor() { }
     explicit Anchor(T t) { hold = t; }
     inline ~Anchor();
-    T &get() { return hold; }
-    const T &get() const { return hold; }
-    void set(const T &t) { hold = t; }
-    void operator=(const T &t) { hold = t; }
-    void clear() { hold = 0; }
 
   private:
     T hold;
+
+    /*
+     * Rooting analysis considers use of operator= to be a use of an anchor.
+     * For simplicity, Anchor is treated as if it contained a GC thing, from
+     * construction. Thus if we had
+     *
+     *   void operator=(const T &t) { hold = t; }
+     *
+     * and this code
+     *
+     *   JS::Anchor<JSString*> anchor;
+     *   stuff that could GC, producing |str|;
+     *   anchor = str;
+     *
+     * the last line would be seen as a hazard, because the final = would "use"
+     * |anchor| that is a GC thing -- which could have been moved around by the
+     * GC. The workaround is to structure your code so that JS::Anchor is
+     * always constructed, living for however long the corresponding value must
+     * live.
+     */
+    void operator=(const T &t) MOZ_DELETE;
+
     Anchor(const Anchor &other) MOZ_DELETE;
     void operator=(const Anchor &other) MOZ_DELETE;
 };

js/public/Value.h

@@ -954,10 +954,6 @@ class Value
         data = STRING_TO_JSVAL_IMPL(str);
     }
 
-    void setString(const JS::Anchor<JSString *> &str) {
-        setString(str.get());
-    }
-
     void setObject(JSObject &obj) {
         MOZ_ASSERT(!IsPoisonedPtr(&obj));
         data = OBJECT_TO_JSVAL_IMPL(&obj);
@@ -1592,7 +1588,6 @@ class MutableValueOperations : public ValueOperations<Outer>
     bool setNumber(uint32_t ui) { return value()->setNumber(ui); }
     bool setNumber(double d) { return value()->setNumber(d); }
     void setString(JSString *str) { this->value()->setString(str); }
-    void setString(const JS::Anchor<JSString *> &str) { this->value()->setString(str); }
     void setObject(JSObject &obj) { this->value()->setObject(obj); }
     void setObjectOrNull(JSObject *arg) { this->value()->setObjectOrNull(arg); }
 };
@@ -1623,7 +1618,6 @@ class HeapBase<JS::Value> : public ValueOperations<JS::Heap<JS::Value> >
     void setBoolean(bool b) { setBarriered(JS::BooleanValue(b)); }
     void setMagic(JSWhyMagic why) { setBarriered(JS::MagicValue(why)); }
     void setString(JSString *str) { setBarriered(JS::StringValue(str)); }
-    void setString(const JS::Anchor<JSString *> &str) { setBarriered(JS::StringValue(str.get())); }
     void setObject(JSObject &obj) { setBarriered(JS::ObjectValue(obj)); }
 
     bool setNumber(uint32_t ui) {

js/src/jsapi.cpp

@@ -1669,11 +1669,6 @@ JS_RemoveScriptRootRT(JSRuntime *rt, JSScript **rp)
     RemoveRoot(rt, (void *)rp);
 }
 
-JS_NEVER_INLINE JS_PUBLIC_API(void)
-JS_AnchorPtr(void *p)
-{
-}
-
 JS_PUBLIC_API(bool)
 JS_AddExtraGCRootsTracer(JSRuntime *rt, JSTraceDataOp traceOp, void *data)
 {

js/src/jsapi.h

@@ -1987,13 +1987,6 @@ JS_RemoveObjectRootRT(JSRuntime *rt, JSObject **rp);
 extern JS_PUBLIC_API(void)
 JS_RemoveScriptRootRT(JSRuntime *rt, JSScript **rp);
 
-/*
- * C-compatible version of the Anchor class. It should be called after the last
- * use of the variable it protects.
- */
-extern JS_NEVER_INLINE JS_PUBLIC_API(void)
-JS_AnchorPtr(void *p);
-
 /*
  * Register externally maintained GC roots.
  *

js/src/jsarray.cpp

@@ -1095,11 +1095,14 @@ ArrayJoin(JSContext *cx, CallArgs &args)
             return false;
         seplen = sepstr->length();
     } else {
-        static const jschar comma = ',';
-        sepchars = ,
-        seplen = 1;
+        HandlePropertyName comma = cx->names().comma;
+        sepstr = comma;
+        sepchars = comma->chars();
+        seplen = comma->length();
     }
 
+    JS::Anchor<JSString*> anchor(sepstr);
+
     // Step 6 is implicit in the loops below
 
     StringBuffer sb(cx);
@@ -1124,9 +1127,6 @@ ArrayJoin(JSContext *cx, CallArgs &args)
             return false;
     }
 
-    // Ensure that sepstr stays alive longer than sepchars.
-    JS_AnchorPtr(sepstr);
-
     // Step 11
     JSString *str = sb.finishString();
     if (!str)

js/src/vm/CommonPropertyNames.h

@@ -33,6 +33,7 @@
     macro(Collator, Collator, "Collator") \
     macro(CollatorCompareGet, CollatorCompareGet, "Intl_Collator_compare_get") \
     macro(columnNumber, columnNumber, "columnNumber") \
+    macro(comma, comma, ",") \
     macro(compare, compare, "compare") \
     macro(configurable, configurable, "configurable") \
     macro(construct, construct, "construct") \