Re: glib main loop concept

[Christian Buennig <masala web de>]

Thanks a lot! This makes things a bit more clear.

One final question:

Is it possible to detect if the default context currently has an active
main loop?
I want to add IO watches to the default context in a library. Apps using
the library may decide to start a main loop themselves (in the default
context) or to let the library do this. Of course they could tell the
library somehow if there already is a running main loop in the default
context, but it would be nice if the library could detect this itself.

jcupitt gmail com wrote:
> On 10/2/07, Christian Buennig <masala web de> wrote:
>> * Do main loops exist per process or per thread?
>>   If I start a main loop in one thread (A) and add an IO watch in
>>   another thread (B), does this watch get added to the main loop of the
>>   thread A or B ?
> 
> Each process can have one or more GMainContext. A context holds a set
> of IO watches, timeouts, callbacks, etc.  There's a default context,
> which is generally the only context. If you use the convenience
> functions g_timeout_add() etc., they will automatically add to the
> default context. You'll need to roll up your own timeout_add() (or
> whatever) if you want to add to a different context.
> 
> Each context can have one or more main loops. These main loops are not
> active at the same time, instead they nest in a stack with only the
> top one active. GTK uses nested main loops to handle modal dialogs. I
> imagine the context and all the main loops for that context have to be
> created and run in a single thread, but I don't know. It would
> certainly reduce confusion if they were.
> 
> So to answer your question, if you have a main loop running in thread
> (A) and add an IO watch from thread (B), the callback on input
> arriving will be called by (A). Unless you go to a lot of trouble to
> add your watch to the non-default context.
> 
>> * If there is only one main loop (regardless of per thread or per
>>   process), why the function g_main_loop_new()?
> 
> This is for the nesting feature.
> 
>> * What's the purpose of the parameter 'is_running' in
>>   g_main_loop_new() ? When should I set it to TRUE and when to FALSE?
> 
> No idea :) I guess you should leave it FALSE and rely on
> g_main_loop_run() to turn this on for you.
> 
> John