Very Computer

by **gar..** » Fri, 10 Mar 2000 04:00:00

Hi,

Here is the code I use to handle signal SIGCHLD. Can anyone tell me why
there's still some zombie processes? I wonder the problem is caused by another
SIGCHLD signal occurs when the program is inside the signal handler. How to
prevent this or why there's zombie processes?(on FreeBSD3.3R)

void chldhdlr(int signo)
{
int status;
pid_t pid;

pid = waitpid(-1, &status, WNOHANG);
}

main()
{
signal(SIGCHLD, &chldhdlr);
/*daemon code here*/
}

--Gareth

by **Rainer Temm** » Fri, 10 Mar 2000 04:00:00

> Here is the code I use to handle signal SIGCHLD. Can anyone tell me why
> there's still some zombie processes? I wonder the problem is caused by
another
> SIGCHLD signal occurs when the program is inside the signal handler. How
to
> prevent this or why there's zombie processes?(on FreeBSD3.3R)

> void chldhdlr(int signo)
> {
> int status;
> pid_t pid;

> pid = waitpid(-1, &status, WNOHANG);
> }

> main()
> {
> signal(SIGCHLD, &chldhdlr);
> /*daemon code here*/
> }

Hi Gareth,

you have to reinstall the signal-handler (call signal(SIGCHLD,chldhdlr);)
after you called waitpid() within your signal-handler.

Regards Rainer

by **Hicna** » Fri, 10 Mar 2000 04:00:00

Quote:>you have to reinstall the signal-handler (call signal(SIGCHLD,chldhdlr);)
>after you called waitpid() within your signal-handler.

or use "sigset", or "sigaction" instead of signal ;)

Regards
Hicnar

by **Andrew Gabri** » Fri, 10 Mar 2000 04:00:00

Quote:
>Hi,

> Here is the code I use to handle signal SIGCHLD. Can anyone tell me why
>there's still some zombie processes? I wonder the problem is caused by another
>SIGCHLD signal occurs when the program is inside the signal handler. How to
>prevent this or why there's zombie processes?(on FreeBSD3.3R)

You don't necessarily see as may SIGCHLD's as you have dead children
waiting to be reaped, as SIGCHLD's are not queued up. Thus in your handler,
you need to reap all those which are currently outstanding, not just one.

Quote:> void chldhdlr(int signo)
> {
> int status;
> pid_t pid;

> pid = waitpid(-1, &status, WNOHANG);
> }

void chldhdlr(int signo)
{
int status;
pid_t pid;

do
{
pid = waitpid(-1, &status, WNOHANG);
}
while (pid > 0);
}

Quote:> main()
> {
> signal(SIGCHLD, &chldhdlr);
> /*daemon code here*/
> }

Whilst I think signal() is safe on BSD (sorry, I can't remember for sure),
it would make your code clearer and more portable if you used sigaction()
instead. sigaction() is consistent across all unixs whereas signal() isn't.

--
Andrew Gabriel
Consultant Software Engineer

by **Andrew Giert** » Fri, 10 Mar 2000 04:00:00

gareth> Hi,

gareth> Here is the code I use to handle signal SIGCHLD. Can anyone
gareth> tell me why there's still some zombie processes? I wonder the
gareth> problem is caused by another SIGCHLD signal occurs when the
gareth> program is inside the signal handler. How to prevent this or
gareth> why there's zombie processes?(on FreeBSD3.3R)

Firstly, always use sigaction() to install signal handlers, not signal().

Secondly, you need to loop in the signal handler:

void chldhdlr(int signo)
{
int status;
pid_t pid;
int saveerrno = errno;

while ((pid = waitpid(-1, &status, WNOHANG)) > 0)
/* do whatever you want to do with PID and STATUS */;

errno = saveerrno;

Quote:}

If you still see zombie processes that persist, then make sure you're
not blocking SIGCHLD inappropriately. (If you do anything in your
signal handler that accesses global data, then you need to block
SIGCHLD when you access that data in your main code, but make sure
that you're unblocking it correctly.)

--
Andrew.

comp.unix.programmer FAQ: see <URL: http://www.erlenstar.demon.co.uk/unix/>
or <URL: http://www.whitefang.com/unix/>

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zombie process?

zombie process?

zombie process?

zombie process?

zombie process?

zombie process?