Re: [Boost-users] [signals (thread safe)] Scope of slot_call_iterator (or how to implement deferred signals)

Subject: Re: [Boost-users] [signals (thread safe)] Scope of slot_call_iterator (or how to implement deferred signals)
From: Frank Mori Hess (fmhess_at_[hidden])
Date: 2009-02-03 20:26:14

On Tuesday 03 February 2009 18:15, Fabio Fracassi wrote:
> I am currently trying to implement deferred signals using boost signals
> (well thread safe signals). I had the (crazy?) idea that it might be
> possible to hijack the combiner interface to do this.
>
> The design rational said that during the signal call the state
> (including the arguments that were passed) are cached for the combiner.
> So, what I tried to do was to copy and store the first and last iterater
> out of the combiner, to iterate over them at a later time, to call the
> slots. What I don't know is whether the slot_call_iterator (and the data
> it uses ) stays in scope after the signal call (i.e.
> signal...::operator() ) returns.

It's definitely not safe to do that with the current implementation, it's 
not a usage I've considered before.  It does seem like it would be 
possible for the library to support what you want to do, adding a feature 
to the slot call iterators similar to what 
boost::shared_container_iterator provides.  My current priority is to 
actually get the library into a release over adding new features though.

My expectation was that someone doing what you are trying to do would 
bundle up the arguments on their own in their slot, to send them off to 
wherever.  It does seem like it could be a convenience to let them copy 
the slot call iterators out of the scope of the signal invocation, since 
the signal has already internally bundled the arguments.