clyde@ut-ngp.UUCP (Clyde W. Hoover) (02/03/84)
<Sacrifice to the wombat god>
Subject: Man leaves processes hanging around, tty modes left scrambled
Index: /usr/src/ucb/man.c 4.2BSD
Description:
Man does not always interact well with job control.
When displaying a manual page using "more" and interrupted,
processes can be left hanging.
Symptoms: there is a 'sh -c' in proc wait (on more)
'more' is in stopped mode.
NOTE: This only happens when using the Cshell.
Cause:
Man and more both trap SIGINT. Man removes temp file, and
more restores terminal modes before exiting.
If man exits before more, then Cshell resets the process
group of the controlling terminal, then when more finally
gets around to restoring tty modes, it is "in the background"
and so gets stopped with SIGTTOU. The shell that fired up
more is hung waiting for more to exit.
Man rolls its own system() so it can use vfork; however
it does NOT ignore SIGINT and SIGQUIT while waiting for
the shell it invoked to exit. If interrupted, man can
exit before its subprocesses do. No problem unless the
subprocesses do things with the terminal - then they will
get stopped with SIGTTOU.
Repeat-By:
Do 'man something' and interrupt at the "--More--" prompt a few
times until man dies and the tty is left in noecho cbreak mode.
Then do a 'ps -ax' to see the hung processes.
Fix:
system(s) (Last routine in man.c)
char *s;
{
int status, pid, w;
int (*saveintr)(), (*savequit)();
if ((pid = vfork()) == 0) {
execl("/bin/sh", "sh", "-c", s, 0);
_exit(127);
}
saveintr = signal (SIGINT, SIG_IGN); /* ***** FIX **** */
savequit = signal (SIGQUIT, SIG_IGN); /* ***** FIX **** */
while ((w = wait(&status)) != pid && w != -1)
;
if (w == -1)
status = -1;
return (status);
(void) signal (SIGQUIT, saveintr); /* ***** FIX **** */
(void) signal (SIGQUIT, savequit); /* ***** FIX **** */
}
--
Clyde W. Hoover @ Univ. of Texas Computation Center; Austin, Texas
(Shouter-To-Dead-Parrots)
clyde@ut-ngp.{UUCP,ARPA} clyde@ut-sally.{UUCP,ARPA} ihnp4!ut-ngp!clyde