Re: Gtkmm Threads question.

[Filipe Apostolo <f apostolo cbr gmail com>]

I'm getting confused here about the Dispatcher, who instantiates the
dispatcher?
The main window, or the system class running in the thread? My first
approach was instantiate a dispatcher in each system thread and when the
calculations where done I emit the signal which would be caught by the
window who owns the treeview.

But in the documentation says that the Dispatcher must be instantiate in
the Receiver thread. This means that I have to create a sigc::signal in
the system thread connect it to a Handler in the window thread and this
handler will emit the dispatcher signal to be caught by other window
handler??

By now I'm not using the dispatcher and I'm using a simple
sigc::signal<void,double> in the system thread, emit it in the
calculations loop, when the calculations are over(each system is
launching this signal each 500milliseconds);

The signal is connected to a handler doing a bind with the threadID, so
in the handler I have all info I need, and the value is passing to the
tree view however I see this is not efficient and there is a big delay
in the update of the "value" column.

I hope you help with my confusion? And suggest me a better solution.

Thanks,
Filipe



Chris Vine wrote:
> On Tue, 12 Jan 2010 16:49:34 +0000
> Filipe Apostolo <f apostolo cbr gmail com> wrote:
>   
>> Hello,
>> happy new year to everyone.
>>
>> I have created a GUI with a treeview, each row of the treeview
>> represents a system with its own calculations and results.
>> Each referred system must  do its calculation in simultaneously, so I
>> launch a thread (Glib::Thread ) to run each system.
>> This is working fine and I'm getting the desired result/behavior.
>>
>> However I want to display the calculated value of each system in the
>> treeview at already created column named "value".
>>
>>
>> I had read that only the main thread is allowed to change widget
>> values. So I must to send the calculated value to the main thread
>> which will identify the sender system and update the value field of
>> this system in the treeview.But I'm not reaching the solution for
>> this.
>>
>> I read about the Glib::Dispatcher and have implemented and I'm
>> connecting  the signal to the handler with success but I cant pass the
>> calculated value through it. And I cant also  make something like:
>> "system[sender_id]->GetValue () " inside the Handler,  because this
>> object is in a loop function (Run()) so the program will crash if the
>> try to access the GetValue.
>>
>> This is simple SingleConsummer (main thread) and multiple producers
>> (each system thread) configuration.
>>
>> I'm working in WindowsXP OS, so I think that I cant use Tunnel like
>> in Unix;
>>
>> What do you suggest me to do? Use Dispatcher, use simple
>> sigc::signal<void,double> to pass the parameters, what does your
>> experience tell you?
>>     
>
> Don't use libsigc++ for this as it is not thread safe (unless you know
> what you are doing).  For a multiple producers and single consumer
> arrangement the best choice is to put the values in an asynchronous
> queue for the consumer to pick up when Glib::Dispatcher emits.
>
> glibmm does not have an asynchronous queue, and if you don't have your
> own one to hand I can e-mail you one I use if you want (there are some
> design wrinkles involved if you want strong exception safety as well as
> thread safety). There was also a bug posted a couple of years ago by a
> user proposing an asynchronous queue for inclusion in glibmm and
> submitting a proposal. It wasn't included, but you can pick that up from
> gnome bugzilla if you want.  The final version of it looked reasonably
> workable.
>
> Chris
>
>
>
>