11-06-2008
Signals...
(posted this in the scripting forum as well, but figured it should go here) So, what's going on is this:
For our program, we had to create our own shell, and if the user pressed ctrl-c just at the cmdline, then this signal would be ignored, but if there is a foreground process running, let's say, "sleep 10", and ctrl-c was pressed, then this process would be terminated... however, my problem lies within background processes... when I press ctrl-c after running something like "sleep 10 &", where the '&' indicates it's a background process, it uses the correct if branch of my SIGINT_handler, but it terminates the process.... so it's definitely something wrong with either the handler, or the installation of the signal.
What I don't get is... if the ctrl-c at the command line doesn't quit the program, why would it terminate my background process? Is it because the parent process just puts the ctrl-c onto the child processes? If so, is there a way to add something to my SIGINT_handler to make it ignore this signal?
****Let me just say that I have successfully been able to ignore the signal for a background process, but this way doesn't use my SIGINT_handler, which I do want it to use so some text gets printed. The way I'm talking of is just using "signal(SIGINT, SIG_IGN)", but like I said, doesn't use my SIGINT_handler...
This is my SIGINT_handler:
void SIGINT_handler(int sig)
{
if (foreground_pid == 0)
{
fprintf(stderr, "\nSIGINT ignored\n");
}
else
{
kill(foreground_pid, SIGINT);
foreground_pid = 0;
}
}
And then when I install the handler/signal, I use signal(SIGINT, SIGINT_handler) and also set foreground_pid in its respective spot... so if anyone can help, that'd be awesome, and if you need to see more code or some things are unclear, ask. Thanks.
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LEARN ABOUT NETBSD
_lwp_kill
_LWP_KILL(2) BSD System Calls Manual _LWP_KILL(2)
NAME
_lwp_kill -- send a signal to a light-weight process
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <lwp.h>
int
_lwp_kill(lwpid_t lwp, int sig);
DESCRIPTION
_lwp_kill() sends the signal specified by sig to the light-weight process specified by lwp. If the sig argument is given as 0 (zero),
_lwp_kill will test for the existence of the target LWP, but will take no further action.
Job control signals and uncatchable signals can not be directed to a specific LWP: if posted with _lwp_kill, they will affect all LWPs in the
process.
Signals will be posted successfully to suspended LWPs, but will not be handled further until the LWP has been continued.
RETURN VALUES
A 0 value indicates that the call succeeded. A -1 return value indicates an error occurred and errno is set to indicate the reason.
ERRORS
[EINVAL] sig is not a valid signal number.
[ESRCH] No LWP can be found in the current process corresponding to that specified by lwp.
SEE ALSO
_lwp_continue(2), _lwp_suspend(2), kill(2), sigaction(2), signal(7)
HISTORY
The _lwp_kill() system call first appeared in NetBSD 5.0.
BSD
January 20, 2007 BSD