kiely@lownlab.UUCP (03/11/87)
Subject: rn hangs when stopped and run in the background
Index: local/usenet/rn/final.c
Description:
When "rn" is stopped with "^Z" and then run in the background
with "bg", it hangs (and the terminal hangs) when restarted
in the foreground with "fg".
Repeat-By:
Warning: this hangs your terminal so be sure to have another
terminal available before trying this.
===================================================
[EDITED] Script started on Wed Mar 11 01:03:06 1987
%
% rn -D
No unread news in subscribed-to newsgroups. To subscribe to a new
newsgroup use the g<newsgroup> command.
******** End of newsgroups--what next? [qnp] ^Zstop_catcher
Stopped
% bg
[1] rn -D &
% cont_catcher
jobs
[1] + Stopped (tty output) rn -D
% bg
[1] rn -D &
/* note that "cont_catcher" is not outputted this time */
% jobs
[1] Running rn -D
% ps
PID TT STAT TIME COMMAND
5744 h3 S 0:00 script
5745 h3 S 0:00 script
5746 p0 S 0:02 -h -i (csh)
5747 p0 T 0:02 rn -D
% jobs
[1] + Running rn -D
% fg
rn -D
/* the terminal hangs at this point */
script done on Wed Mar 11 01:04:50 1987
=======================================
Fix:
Under 4.2 BSD, SIGCONT *is* blocked for the duration of the
SIGCONT handler. For this application, SIGCONT must be
unblocked immediately on entering the handler or any signal
that causes the process to stop will cause the process to hang
since it cannot be restarted while SIGCONT is blocked.
This may or may not be an kernel bug. The way I read the
documentation in section 2 of the manual SIGCONT cannot be blocked.
The interpretation that SIGCONT cannot be blocked by the
user but is blocked for the duration of the SIGCONT handler
must be the correct interpretation because that is the way that
it works. This has been tested with an Integrated Solutions
Optimum 5/10 running 4.2BSD (ISI release 3.05), a VAX 8200
running Ultrix 1.2, and a MicroVaxII running 4.3BSD.
Context diff's follow.
RCS file: RCS/final.c,v
retrieving revision 4.3.1.1
diff -c -r4.3.1.1 final.c
*** /tmp/,RCSt1005819 Wed Mar 11 01:24:31 1987
--- final.c Wed Mar 11 01:22:36 1987
***************
*** 205,210
cont_catcher()
{
sigset(SIGCONT,cont_catcher);
savetty();
# ifdef MAILCALL;
mailcount = 0; /* force recheck */
--- 211,219 -----
cont_catcher()
{
sigset(SIGCONT,cont_catcher);
+ # ifdef BSD42
+ sigsetmask(sigblock(0) & ~(1 << (SIGCONT-1)));
+ # endif /*BSD42*/
savetty();
# ifdef MAILCALL;
mailcount = 0; /* force recheck */
============================================================================
NAME: James P. Kiely USPS: Kiely Laboratories
USENET: ...!harvard!lownlab!kiely P.O. Box 624
DOMAIN: kiely@lownlab.harvard.edu Allston, MA 02134-0624
PHONE: +1 617 782 4136 USA