Re: [Boost-users] [dataflow.signals][thread_safe_signals] How to alter the Calling of chained signals

From: Manuel Jung (gzahl_at_[hidden])
Date: 2008-08-28 16:19:24

Stjepan Rajko wrote:
Hi,

Here are some of my thoughts. Still not ver much time, more around the
weekend.

> On Mon, Aug 25, 2008 at 11:40 AM, Stjepan Rajko <stipe_at_[hidden]> wrote:
>> On Sun, Aug 24, 2008 at 11:51 AM, Manuel Jung <gzahl_at_[hidden]> wrote:
>>>
>>> An example would be really great! Do you know the proposed threadpool
>>> library?
>>>
>>
>> I just downloaded it and need to study it a bit.  When I figure out
>> how to use it, I'll work on the example.
>>
> 
> OK, I have a working example.  You can find it in the boost sandbox:
> 
>
http://svn.boost.org/svn/boost/sandbox/SOC/2007/signals/libs/dataflow/example/threadpool/threadpool_example.cpp

I checked out the whole dataflow from sandbox. Example compiles and runs
fine.

> 
> The user code looks like this:
> 
> typedef
>     tp::pool<
>         tp::fixed,
>         tp::unbounded_channel< tp::fifo >
>     > threadpool_type;
> 
> threadpool_type pool(tp::max_poolsize(5));
> 
> typedef boost::signals::storage<void(int)> source_type;
> typedef boost::signals::function<void(int), int(int)> filter_type;
> 
> // our components
> source_type source(1);
> filter_type increase(inc_fn);
> filter_type increase2(inc_fn);
> filter_type increase3(inc_fn);
> filter_type increase4(inc_fn);
> 
> // our network
> //  increase >>= increase2 will be in its own thread
> //  increase3 will be in its own thread
> //  increase4 will be in its own thread
> source
>     | (make_delay(pool, increase) >>= increase2)
>     | (make_delay(pool, increase3) >>= make_delay(pool, increase4));
> 
> // submit the first task
> submit(pool, source);
> 

This seems very usable. I also like that you are able to add filters to
different pools.

> 
> Like you said, delay might not be the best name, but works for now.  A
> couple of comments:
> 
> * The example is hard-wired to a void(int) signature.  It wouldn't be
> hard to generalize, if there is interest.

I need to have it generalize. Would be great if you could do it, otherwise,
i'll try at the weekend.

> 
> * The example above uses Boost.Signals (not thread_safe_signals).
> This is unsafe, but in my experience as long as the signals get
> connected before the threading starts, it works ok.  A couple of minor
> things need to be addressed with thread_safe_signals before it will
> work as a drop-in replacement with Dataflow.Signals - I'll see if I
> can get them integrated.

Hmm. thread_safe_signals are needed too. There will be new signal
connections after the threading.

> 
> * I don't use chained_submit - instead, the delay object will do a
> regular submit when it gets its input.  This was more in line with the
> push-oriented design of Boost.Signals.  To use chained_submits and
> futures would require either using a pull-based network (each
> component taking in the input as the argument and returning the
> result), or propagating the final result back through return values.
> 

That is ok with me. I would prefer all the tasks to be added at the
beginning (because of an easier priority handling of the queue), but i can
this way too, i think.

> Thoughts?

Seems very great so far. This way you can do late evaluated dataflow
networks :-). Just create a pool and make a dataflow network (even a
cyclic! :-)) and you could evaluate it step for step, depending by the
threadpools queueing pollicy.

Thanks for what you did so far :-). I like the dataflow lib. Can i help
writing some code, the generalization for all data types or something else?
I just don't know the inside of the dataflow library that good, it would
take much longer, if i try to do it... but im of course willing to help.
Maybe an other example?

> 
> Stjepan

Kind Regards
Manuel