Frank Mori Hess wrote:
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On Friday 23 February 2007 12:22 pm, Peter Dimov wrote:
I actually like the suggestion of just offering a way to add the tracked pointers manually. Either
sig.connect( boost::bind( myfunction, boost::ref(coord->x) ), coord );
or
sig.connect( boost::bind( myfunction, boost::ref(coord->x) ).track( coord );
Both look better on a syntactic level to me. In addition, I suspect that signalslib::track contains a race condition that is avoided by the other alternatives (but I haven't actually looked at it so I might be wrong; it's possible, if somewhat tedious, to implement it correctly).
Would you elaborate on the race you are thinking of? Putting track in the connection class instead of the slot class makes races possible, since the connection is established before the tracked objects are added. Admittedly, this is only a problem if you are holding the tracked objects as weak_ptrs before giving them to the signal.
This isn't very likely since you won't be able to use coord->x if you only have a weak_ptr. Typically you'll lock() and connect if that succeeds. The temporary shared_ptr will ensure that there is no race. This is easy to enforce if track() takes a shared_ptr instead of a weak_ptr. The singalslib::track race occurs if you have T* get_pointer( something_like_weak_ptr<T> p ) { return shared_ptr<T>( p ).get(); } There is a small window where it's possible for the weak_ptr to expire while the caller of get_pointer is holding a T*.