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SubjectRe: 2.6.14-rc1 wait()/SIG_CHILD bevahiour
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On Mon, 2005-09-19 at 14:01 -0400, Kyle Moffett wrote:
> On Sep 19, 2005, at 13:39:33, Badari Pulavarty wrote:
> > Hi,
> >
> > I am looking at a problem where the parent process doesn't seem to
> > cleanup the exited children (with a webserver). We narrowed it down
> > to a simple testcase. Seems more like a lost SIG_CHILD.
>
> You don't get one SIG_CHLD per child that quits. The kernel may and
> probably will merge SIG_CHLD signals together if it has several
> queued before it gets a chance to deliver them to your process. This
> is true of _all_ signals. If you "kill -STOP 1234", then "kill -QUIT
> 1234", "kill -QUIT 1234", "kill -QUIT 1234", "kill -CONT 1234", the
> PID 1234 will have 3 signals delivered: The original untrappable
> SIGSTOP, the SIGCONT that causes it to resume, and a single SIGQUIT

True.

> immediately following it. The correct and portable way to handle
> this is to put a loop in your SIGCHLD signal handler:
>
> #include <sys/types.h>
> #include <sys/wait.h>
>
> void sigchld_handler(int signal) {
> pid_t pid;
> int status;
>
> while( -1 != (child = waitpid(-1, &status, WNOHANG)) ) {
> /*
> * Now "status" is the exit status of the child and
> * "pid" is its pid. See the waitpid() manpage for
> * macros you can use to get information from the
> * status variable.
> */
> do_some_processing_of_exited_child(pid,status);
> }
> }


Thats what I already do, in my current testcase.

while(1) {
pid = wait4(-1, &status, WNOHANG, &ru);
if (pid <= 0) break;
// printf("SIGCHLD received for pid %d\n", pid);
pid_exited(pid);
}


Thanks,
Badari

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