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


> -----Original Message-----
> From: Felipe Contreras [mailto:felipe.contreras@nokia.com]
> Sent: Tuesday, October 26, 2010 12:03 PM
> To: Guzman Lugo, Fernando; felipe.contreras@gmail.com
> Cc: gregkh@suse.de; hiroshi.doyu@nokia.com;
> linux-kernel@vger.kernel.org; andy.shevchenko@gmail.com;
> linux-omap@vger.kernel.org; linux-arm-kernel@lists.infradead.org
> Subject: RE: [PATCH 8/8] staging: tidspbridge - make
> sync_wait_on_event interruptible
>
> fernando.lugo@ti.com wrote:
> > > On Tue, Oct 26, 2010 at 3:51 AM, Fernando Guzman Lugo
> > > <x0095840@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
>

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