Re: [boost] [Signals] Named slot group usage?

From: Doug Gregor (dgregor_at_[hidden])
Date: 2005-02-11 11:34:18

On Feb 11, 2005, at 9:51 AM, Peter Dimov wrote:

> Douglas Gregor wrote:
>> Background: Signals performance is sub-par, and much of the problem
>> can be traced back to support for named slot groups. I'm trying to
>> determine the best way to proceed.
>
> Are you sure that this is the case?

There may be other issues, but going from a std::list to a std::map (as 
needed to efficiently support connection of named slots) hurts 
iteration performance and increases executable code size. To counter 
the latter problem, I've done some type erasure that slows it down 
further and causes some of the extra heap allocations :(

> 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.

It's not quite that bad in Signals; there's a boolean flag in each 
connection that checks whether the slot has been disconnected. If we're 
in the process of invoking slots (recursively), disconnection merely 
marks the slot as having been removed. Once the top-level signal 
invocation completes, it scans the slot list to remove any slots that 
were marked as disconnected. This does hurt iteration performance 
(because we have to skip over disconnected slots) and slots down the 
top-level invocation slightly (because the list is rescanned).

        Doug