On Fri, 11 Feb 2005 16:51:48 +0200 "Peter Dimov" <pdimov@mmltd.net> wrote:
Last time I looked, alternatives beat Boost.Signals because they don't
handle the corner cases of slot disconnection during signal invocation.
Example:
R operator()(void) const { typename list::iterator i = list_.begin(); while (i != list_.end()) { if (i->function_) { (i++)->function_(); } else { i = list_.erase(i); } } }
(from Jody Hagins's implementation)
AFAICS this doesn't work if (i++)->function_() disconnects *(i+1).
To handle disconnection correctly, one needs to invoke a temporary list<>. I haven't looked at what boost::signal does, but this may account for the dynamic allocations that have been reported.
That implementation was a very first try at something for comparison purposes. Because of the performance differences, I modified that code a bit and added a few pieces of functionality, one of which is the ability to replace a slot and/or disconnect a slot while it is being handled. The performance difference was measurable, but very small. A copy of the list is not necessary to implement this feature.