Changeset 119341 in webkit for trunk/Source/JavaScriptCore/heap/Weak.h

Timestamp:

Jun 2, 2012, 3:49:05 PM (13 years ago)

Author:

[email protected]

Message:

DOM string cache should hash pointers, not characters
​https://bugs.webkit.org/show_bug.cgi?id=88175

Reviewed by Phil Pizlo and Sam Weinig.

../JavaScriptCore:

• heap/Weak.h:

(JSC::weakAdd):
(JSC::weakRemove): Made these function templates slightly more generic
to accommodate new client types.

../WebCore:

Dromaeo DOM Core reports no change.

​http://trac.webkit.org/changeset/84934 accidentally changed from hashing
pointers to hashing characters, due to template defaults. Let's change back.

Hashing characters is not so good because:

(1) It's not memory-safe with HashMap::set(). HashMap::set() replaces
the value but not the key. Since our values own our keys, we need to
ensure object identity between key and value, or the key can be freed
prematurely. (This is impossible to demonstrate with our current
eager sweep behavior, but it shows up as crashes in layout tests if you
change to lazy sweep.)

(2) It's slower.

• bindings/js/DOMWrapperWorld.h:

(WebCore): Override the default hash, which hashes based on characters.

File:

• trunk/Source/JavaScriptCore/heap/Weak.h (modified) (2 diffs)

trunk/Source/JavaScriptCore/heap/Weak.h

@@ -154 +154 @@
 // This function helps avoid modifying a weak table while holding an iterator into it. (Object allocation
 // can run a finalizer that modifies the table. We avoid that by requiring a pre-constructed object as our value.)
-template<typename T, typename U> inline void weakAdd(HashMap<T, Weak<U> >& map, const T& key, PassWeak<U> value)
+template<typename Map, typename Key, typename Value> inline void weakAdd(Map& map, const Key& key, Value value)
 {
     ASSERT(!map.get(key));
@@ -160 +160 @@
 }
 
-template<typename T, typename U> inline void weakRemove(HashMap<T, Weak<U> >& map, const T& key, typename Weak<U>::GetType value)
-{
-    typename HashMap<T, Weak<U> >::iterator it = map.find(key);
+template<typename Map, typename Key, typename Value> inline void weakRemove(Map& map, const Key& key, Value value)
+{
+    typename Map::iterator it = map.find(key);
     ASSERT_UNUSED(value, value);
     ASSERT(it != map.end());