[PATCH 8/8] staging: tidspbridge - make sync_wait_on_event interruptible

[Guzman Lugo, Fernando]

> -----Original Message-----
> From: Felipe Contreras [mailto:felipe.contreras at nokia.com] 
> Sent: Tuesday, October 26, 2010 12:03 PM
> To: Guzman Lugo, Fernando; felipe.contreras at gmail.com
> Cc: gregkh at suse.de; hiroshi.doyu at nokia.com; 
> linux-kernel at vger.kernel.org; andy.shevchenko at gmail.com; 
> linux-omap at vger.kernel.org; linux-arm-kernel at lists.infradead.org
> Subject: RE: [PATCH 8/8] staging: tidspbridge - make 
> sync_wait_on_event interruptible
> 
> fernando.lugo at ti.com wrote:
> > > On Tue, Oct 26, 2010 at 3:51 AM, Fernando Guzman Lugo 
> > > <x0095840 at ti.com> wrote:
> > > > So that avoid non-killable process.
> > > 
> > > It would be useful to interrupt these tasks from user-space. 
> > > A separate ioctl to do that would be needed.
> > 
> > I don't see use case where that could be needed. It is only 
> To avoid a 
> > nonkillable task in the case the user pass an infinite Timeout.
> > 
> > If you have some test case where that ioctl would be needed Please 
> > share it in order to find the best solution.
> 
> Well, imagine the application is using a library to access 
> the DSP, and the library has a dedicated thread listening for 
> DSP events in a loop.
> This happens to be how libomxil-ti and gst-dsp work.
> 
> Now, the thread received the last message, but has set a 
> timeout of 10s, or even worst, no timeout at all.
> 
> After realizing that was the last message, the main thread 
> decides to shut down, but it has to wait for the DSP thread 
> to join. Unfortunately the DSP thread is stuck waiting for 
> events, and there's nothing that can be done.
> 
> However, if we have a separate ioctl to interrupt that task, 
> then the main thread can issue that ioctl, and unlock the DSP 
> thread without having to wait 10s, or forever.
> 
> Does that make sense?

Maybe sending a signal to yourselft and having a dummy signal
Handle should work, it that would not like good. I am thinking
On having a ioctl to create and set an event the you could
Something like this:

struct dsp_notification events[3];

proc_register_notify(proc, event_type, &events[0]);
...
proc_register_notify(proc, event_type, &events[1]);
...
Sync_open_event(&events[2]);


second thread:

	mgr_wait_for_bridge_events(proc, events, 3, index);

	if (index == 2) 
		/* main thread force exit */


Main thread:

	/* if some execption happened then finish the second thread */
	sync_set_event(events[2]);

	pthread_join(...);


However it is in progess a task for change replacing dspbridge sync.c
Module with event_fd to signal events to userspace. Where now simple
File descriptor will be used as event elements. So the mgr_wait_for_bridge_events
Will be implemented using "select" system call inside to wait for multiple events.
So you will be able to do something like this:

int events[3];

proc_register_notify(proc, event_type, &events[0]);
...
proc_register_notify(proc, event_type, &events[1]);
...
events[2] = eventfd(0, 0);


second thread:

	mgr_wait_for_bridge_events(proc, events, 3, index);

	if (index == 2) 
		/* main thread force exit */

Main thread:

	/* if some execption happened then finish the second thread */
	write(events[2], "s", 1);

	pthread_join(...);

You won't need any aditional ioctl in order to do what you want to do.

So, I think it is not worth to make much changes to some module that will
Dissapear (my patch is just a fix it is not implementing something new),
It is just a matter of time to that task is finished and tested properly
And then send to LO.

Regards,
Fernando.

> 
> --
> Felipe Contreras
>