This function essentially limits the life time of the
closure to the life time of the object.
That is, when the object is finalized, the
closure is invalidated by calling
invalidate on it, in order to prevent invocations of the closure with a
finalized (nonexisting) object. Also, @ref and
unref are added as marshal guards to the
closure, to ensure that
an extra reference count is held on this during invocation of the
closure. Usually, this function
will be called on closures that use this this as closure data.
Object restricting lifetime of
Closure to watch