[Xenomai-help] Re : rt_printf with daemonized task

[oliver.schlenker@domain.hid]

-------- Original Message --------
Subject: Re: Re-8:  rt_printf with daemonized task (07-Okt-2009 17:38)
From:    Jan Kiszka <jan.kiszka@siemens.com>
To:      oliver.schlenker@smmotioncontrol.de

> oliver.schlenker@smmotioncontrol.de wrote:
> > 
> > 
> > As you expected, changing the syslog call from
> >     syslog( LOG_ERR | LOG_LOCAL4, head->text ); 
> > to
> >     syslog( LOG_ERR | LOG_LOCAL4, "%s", head->text ); 
> > 
> > did not change anything.
> > 
> > To track down the problem further, I have made a small test application :
> > 
> > #include <stdlib.h>
> > #include <stdio.h>
> > 
> > #include <native/task.h>
> > #include <native/timer.h>
> > #include <rtdk.h>
> > 
> > 
> > int main( int arc, char *argv[] )
> > {
> > int i;
> > 
> > rt_print_auto_init(1);
> > 
> > rt_printf("--------------- TEST RT-PRINTF  1 ------------\n");
> > 
> > 	sleep(1);
> > 
> > daemon(0,0);
> > 
> > 	rt_print_auto_init(1);
> > 
> > 	rt_printf("--------------- TEST RT-PRINTF  2 ------------\n");
> > 
> > 	sleep(10);
> > 
> > return(0);
> > }
> > 
> > 
> > 
> > This application gives the following results :
> > - If the daemon() function is not called, all rt_printf() do work well
> >   and output is shown in syslog
> > - If daemon() function is called, and first call to sleep(1) is omitted,
> >   there is no output in the syslog whatsoever.
> > - If daemon() function is called, and first call to sleep(1) is executed,
> >   there is output of the first rt_printf in the syslog but not of the 
> > second
> >   one.
> > 
> > I do not have any idea why daemonizing of the process is not giving
> > any output to the syslog.
> 
> As you are already looking at rt_printf.c: __rt_print_init spawns a
> pthread that polls the internal queues and issues the output to stdout
> or whatever. On fork (or daemonize), this thread is not replicated. So
> the child process simply has no printing thread.

Ok, understood, at least for the scenario where the rt_print feature is initialised
befor the fork/daemon call.
What I don't understand is, why it does not work if the rt_print feature is initialised after the fork / daemon.

> 
> I think this should be fixable with a pthread_atfork hook, patches
> always welcome.

I would like to follow up this track. I have to have a look at pthread_atfork first,
because I'm not so familiar with the pthread functions.
Therefor any hint what should be done with pthread_atfork is very welcome.


> 
> Jan
> 
> -- 
> Siemens AG, Corporate Technology, CT SE 2
> Corporate Competence Center Embedded Linux



Oliver

To: jan.kiszka@siemens.com
Cc: gilles.chanteperdrix@xenomai.org
    xenomai-help@gna.org