process doesn't terminate when closing streams from another thread

process doesn't terminate when closing streams from another thread

[Nuno Gonçalves]

I'm having problems when closing streams from another thread.

The following code:

static void *func(void *arg)
{
   fclose(stdout);
   fprintf(stderr,"Thread about to exit\n");
   return 0;
}

int main(int argc, char **argv)
{
   int thread_id;
   pthread_create(&thread_id,NULL,&func,NULL);
   pthread_join(thread_id,NULL);
   fprintf(stderr,"Process about to terminate\n");
   return 0;
}

Prints:

root@OpenWrt:/tmp# ./myapp_withmusl
Thread about to exit
Process about to terminate

But never returns! I have to send it a SIGINT.

This happens on target-mips_34kc_musl-1.1.11.

Thanks,
Nuno

Re: process doesn't terminate when closing streams from another thread

[Szabolcs Nagy]

* Nuno Gon?alves <nunojpg@gmail.com> [2015-09-06 15:44:45 +0100]:
> I'm having problems when closing streams from another thread.
> 
> The following code:
> 
> static void *func(void *arg)
> {
>    fclose(stdout);
>    fprintf(stderr,"Thread about to exit\n");
>    return 0;
> }
> 
> int main(int argc, char **argv)
> {
>    int thread_id;

s/int/pthread_t/

>    pthread_create(&thread_id,NULL,&func,NULL);
>    pthread_join(thread_id,NULL);
>    fprintf(stderr,"Process about to terminate\n");
>    return 0;
> }
> 
> Prints:
> 
> root@OpenWrt:/tmp# ./myapp_withmusl
> Thread about to exit
> Process about to terminate
> 
> But never returns! I have to send it a SIGINT.
> 

yes, musl fflushes stdout on fflush(0) even if
it is closed. (fflush(0) is called at exit,
fflushing a closed stream is undefined behaviour).

this might be a musl bug.

Re: process doesn't terminate when closing streams from another thread

[Rich Felker]

On Sun, Sep 06, 2015 at 07:00:33PM +0200, Szabolcs Nagy wrote:
> * Nuno Gon?alves <nunojpg@gmail.com> [2015-09-06 15:44:45 +0100]:
> > I'm having problems when closing streams from another thread.
> > 
> > The following code:
> > 
> > static void *func(void *arg)
> > {
> >    fclose(stdout);
> >    fprintf(stderr,"Thread about to exit\n");
> >    return 0;
> > }
> > 
> > int main(int argc, char **argv)
> > {
> >    int thread_id;
> 
> s/int/pthread_t/
> 
> >    pthread_create(&thread_id,NULL,&func,NULL);
> >    pthread_join(thread_id,NULL);
> >    fprintf(stderr,"Process about to terminate\n");
> >    return 0;
> > }
> > 
> > Prints:
> > 
> > root@OpenWrt:/tmp# ./myapp_withmusl
> > Thread about to exit
> > Process about to terminate
> > 
> > But never returns! I have to send it a SIGINT.
> > 
> 
> yes, musl fflushes stdout on fflush(0) even if
> it is closed. (fflush(0) is called at exit,
> fflushing a closed stream is undefined behaviour).
> 
> this might be a musl bug.

Yes, this is indeed a musl bug. Getting the right fix is non-trivial
but I think it will involve having fclose unlock the FILE but ensure
that its contents are setup such that the exit-time code behaves as a
no-op.

Rich

Re: process doesn't terminate when closing streams from another thread

[Rich Felker]

On Sun, Sep 06, 2015 at 03:44:45PM +0100, Nuno Gonçalves wrote:
> I'm having problems when closing streams from another thread.
> 
> The following code:
> 
> static void *func(void *arg)
> {
>    fclose(stdout);
>    fprintf(stderr,"Thread about to exit\n");
>    return 0;
> }
> 
> int main(int argc, char **argv)
> {
>    int thread_id;
>    pthread_create(&thread_id,NULL,&func,NULL);
>    pthread_join(thread_id,NULL);
>    fprintf(stderr,"Process about to terminate\n");
>    return 0;
> }
> 
> Prints:
> 
> root@OpenWrt:/tmp# ./myapp_withmusl
> Thread about to exit
> Process about to terminate
> 
> But never returns! I have to send it a SIGINT.
> 
> This happens on target-mips_34kc_musl-1.1.11.
> 
> Thanks,

Thanks for the report. This should now be fixed (in git master). Let
me know if you still have problems.

Rich