hulsebos@ehvie0.tq.ine.philips.nl (rob hulsebos) (12/15/89)
When I run this program on my System V.2 or V.3 box, and then
send it a SIGTERM signal, the loop in "die()" is executed until
the "sleep" terminates. From that moment on, the loop in "main()"
is executed.
This is not the behaviour I expect: the routine "die()" should
*not* exit but continue to execute. Apparently, when the SIGALRM
goes off inside "sleep", the kernel executes the signal-handler
internal to "sleep", but forgets to return to the original
signal-handling routine "die()" it was executing.
From this I conclude that signal-handling routines can not be stacked
on a V.2 or V.3 system (it works as expected on BSD), probably because
of a setjmp/longjmp construction in "sleep". Am I correct, or is there
something wrong in V.2/V.3, or is this a bug in my system?
#include "signal.h"
int die();
int flag = 1;
main()
{
int i;
signal(SIGTERM, die );
while(1 )
{
sleep(1 );
if (!flag )
write(1, "!flag\n", 6 ); /* should not be printed */
}
}
die()
{
flag = 0;
while(1 )
write(1, "signal\n", 7 );
}
When you've compiled this program, run it in the background and then
send it a SIGTERM. A few lines of "signal" will be printed followed
be lines with "!flag".
From this I conclude that signal-handling routines can not be stacked
on a V.2 or V.3 system (it works as expected on BSD), probably because
of a setjmp/longjmp construction in "sleep". Am I correct, or is there
something wrong in V.2/V.3, or is this a bug in my system?
-------------------------------------------------------------------------------
Rob Hulsebos == hulsebos@tq.ine.philips.nl Tel +31-40-785723, Fax +31-40-786114
Philips I&E - Where the future is being made today!gcardwel@orion.oac.uci.edu (Guy Cardwell) (12/16/89)
In article <608@ehvie0.tq.ine.philips.nl> hulsebos@ehvie0.tq.ine.philips.nl (rob hulsebos) writes: >From this I conclude that signal-handling routines can not be stacked >on a V.2 or V.3 system (it works as expected on BSD), probably because >of a setjmp/longjmp construction in "sleep". Am I correct, or is there >something wrong in V.2/V.3, or is this a bug in my system? One of the major "innovations" in BSD over Sys V was the fact that signals are stacked. Some implementations may support it. (AIX, for example) Guy -- look.... even a test signature.....