Bug 27163
| Summary: | sh trap TSTP ( ) deadly hangs | ||
|---|---|---|---|
| Product: | Base System | Reporter: | Jin Guojun <jin> |
| Component: | bin | Assignee: | Martin Cracauer <cracauer> |
| Status: | Closed FIXED | ||
| Severity: | Affects Only Me | ||
| Priority: | Normal | ||
| Version: | 4.3-RELEASE | ||
| Hardware: | Any | ||
| OS: | Any | ||
Responsible Changed From-To: freebsd-bugs->cracauer Martin maintains /bin/sh State Changed
From-To: open->closed
Closing, correct behaviour.
In this script...
trap "echo do not try this; exit" TSTP
while [ 1 ] ; do
date
sleep 2
done
... the trap handler for the SIGTSTP is correctly never invoked. The
reason is that the sleep(1) or date(1) are stopped and hence never
return. Trap handlers are excuted after the child exits - which never
happens here.
If the program being called is catching SIGTSTP, and is hence not
stopped and then exits later, the handler is correctly excuted:
Compile this to ./obscure
#include <stdio.h>
#include <signal.h>
void onsig(int signo)
{
fprintf(stderr, "foobarn"); /* yes I know, not allowed */
exit(1);
}
int main(void)
{
signal(SIGTSTP, onsig);
for (;;)
;
return 0;
}
And run this:
trap "echo do not try this; exit" TSTP
while [ 1 ] ; do
./obscure
done
The above trap will be executed at the correct time.
I love this stuff, how could I live without it for no many moons :-)))
|
According to the signal manpage: Except for the SIGKILL and SIGSTOP signals, the signal() function allows for a signal to be caught, to be ignored, or to generate an interrupt. These signals are defined in the file <signal.h>: Name Default Action Description ... Would this imply that /bin/sh can trap (catch) the SIGTSTP ? However, it is not. Try the following script, it deadly hangs if "" pressed. How-To-Repeat: ---------- sh script ----- trap "echo do not try this; exit" TSTP while [ 1 ] ; do date sleep 2 done ---------- end of sh script ----- sh script Sun May 6 13:26:05 PDT 2001 Sun May 6 13:26:07 PDT 2001