Looking at how refcounting is implemented in WebCore, I was surprised
to find that there are a lot of functions/methods that take
PassRefPtr<>s as parameters instead of regular pointers to those
objects. I can't see any benefit to this, and it adds the overhead of
a ref() and deref() at every call-site.
For example in HTMLNameCollection.h:
HTMLNameCollection(PassRefPtr<Document>, CollectionType, const
String& name);
Why shouldn't this be
HTMLNameCollection(Document*, CollectionType, const String& name);
?
The use of PassRefPtr instead of RefPtr here also seems prone to
trouble, since inside the implementation of the method it could end up
unexpectedly clearing the parameter:
HTMLNameCollection::HTMLNameCollection(Document* doc, .... {
Ref<Document> otherDoc = doc; // This sets doc to NULL!
doc->something(); // CRASH
}
I ran across this while trying to track down a reference leak of a
Document object. As one of my last resorts I set a watchpoint on the
object's m_refcount to see who refs/derefs it; but I had to give up
because so many method calls, including the one above, keep constantly
twiddling the refcount while passing the Document as a parameter.
—Jens
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