[9fans] handling notes

[9fans] handling notes

[Joel “chesky” Salomon]

I'm doing an exercise for my Operating Systems class here at Cooper, and I'm supposed to be catching signals.  The professor was nice enough to let me catch notes on Plan 9 if I could make that work.

The code is at <http://www.tip9ug/who/chesky/src/katp.c> and <http://www.tip9ug/who/chesky/src/wdp.c>.  Basically, katp installs a note handler with atnotify then spawns a pager to catenate its command-line aguments to.  Wdp, the World’s Dumbest Pager, reads a single ½KB chunk from stdin then closes it and exits.

Eventually, katp is supposed to recognize that the pipe is closed and respawn wdp; I’m not there yet.  Right now, I can’t get the note handler to print anything on pipe close.  If I add a sleep(long time) somewhere and interrupt it, the handler reports it; just not for the closed pipe.

What am I missing or doing wrong?

Thanks,
--Joel

Re: [9fans] handling notes

[Russ Cox]

Try a bigger file, like /dev/zero.
Or insert a sleep(500) after the write in cat.

Why either of those would fix the problem is
an exercise to the reader.  ;-)

Russ

Re: [9fans] handling notes

[Joel “chesky” Salomon]

> Try a bigger file, like /dev/zero.
> Or insert a sleep(500) after the write in cat.
> 
> Why either of those would fix the problem is
> an exercise to the reader.  ;-)

I tried /lib/keyboard as input, and saw the breadcrumb from program end before the end of output; the parent process dies before the pipe breaks!

I’m putting the sleep(500), properly commented, (what manual section is sleep(500) in? ☺) into cat to get the same effect.  Thanks, Russ!

Now for the detection and respawning...  I’ll hold off on asking for hints for a little while and try to figure it out myself.

Good nigh— ye flipplin’ gods, it’s already morning! — folks,
--Joel