[LAD] Inter thread Communication: Design Approach

[Florian Paul Schmidt]

On 09/02/2011 12:04 PM, Fons Adriaensen wrote:
> On Thu, Sep 01, 2011 at 03:54:03PM -0400, Paul Davis wrote:
>> On Thu, Sep 1, 2011 at 2:37 PM, Fons Adriaensen<fons at linuxaudio.org>  wrote:
>>
>>> That's assuming that the event's virtual execute() has access to
>>> all it needs. In all cases I've encountered that is not the case:
>>> the event triggers something in the context where it is received
>>> and processing it requires access to that context's data.
>>> It's a problem for which I don't know a clean C++ solution.
>> depending on the exact type of thing you're talking about, isn't this
>> is place for closures, functors, etc. etc. ?
> Yes, but
>
> 1. I find functor syntax extremely clumsy, involving the creation of
>     a specific derived functor class (from a template class) for each
>     one you need.
>
> 2. AFAIK (using the terminology of<http://www.newty.de/fpt/functor.html>,
>     you can't have a TSpecificFunctor member in the event class and
>     initialise it, it has to be a TSpecificFunctor*. Which in turn
>     means that at the sender side you either have instances of all
>     possibly required functor classes available and assign the
>     TSpecificFunctor* in the event from one of them, or you have to
>     use new() to allocate one. The former is extremely clumsy, and
>     the latter shouldn't be done in a RT context.
>
> What I'm missing in C++ is a built-in 'functor' type that can
> simply be assigned from any object::method, with the user being
> responsible for the existence of the object and for supplying the
> right arguments at the time the functor is called.
>
>

boost::function<void(void)> serves this purpose for me in jass. To 
create and pass a functor that assigns a new auditor generator to the 
one in the engine, and then tells it to play i do for example:

write_blocking_command(assign(engine_.auditor_gen, p));
write_blocking_command(boost::bind(&engine::play_auditor, 
boost::ref(engine_))); assign() is just a utility template to make 
creating functors that do assignments easier.. boost::bind is used to 
make all passed functors 0-ary (e.g for binding member functions to 
their instance or binding arguments to the functor.. and 
write_blocking_command is just a utility function that disables the GUI 
until the acknowledgement from the engine has come back to the GUI,, The 
command ringbuffer is just a ringbuffer holding 
boost::fucntion<void(void)> objects..

typedef ringbuffer<boost::function<void(void)> > command_ringbuffer;

Examples from here: 
https://github.com/fps/jass/blob/master/main_window.h 
https://github.com/fps/jass/blob/master/assign.h 
https://github.com/fps/jass/blob/master/engine.h Regards, Flo



> Ciao,
>