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Postings from January 2001
$ ./a.out
wait pend=1 status=0
$ uname -a
dgux t4 R4.11MU04 generic AViiON PentiumPro
nick@ing-simmons.net wrote:
> I am playing with safe signals again.
>
> With this scheme C code just sets a pending flag, and then perl level
> handler is called next time round the runops loop.
>
> I have a half remembered worry. I seem to recall some system where
> if the SIGCHLD signal handlder did not do a wait() of some kind
> then when it returned SIGCHLD was posted again, and again, and ...
>
> The attached program attempts to test for this case.
> Will those of you with various UNIXes try it please?
> (Linux+glibc is okay).
>
> If I have remembered correctly, then on such awkward systems we need
> to do a wait() in the handler and save status somewhere. Which is a
> pain as one does not know (in the general case) the pid in advance
> to pre-allocate storage.
>
> --
> Nick Ing-Simmons
>
> -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> #define PERLIO_NOT_STDIO 0
> #include "EXTERN.h"
> #include "perl.h"
>
> #if 0
>
> #include <stdio.h>
> #include <sys/time.h>
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <signal.h>
> #include <unistd.h>
> #include <errno.h>
>
> #endif
>
> int pending;
>
> #ifndef SIGCHLD
> #define SIGCHLD SIGCLD
> #endif
>
> void
> catch(int sig)
> {
> pending++;
> if (pending > 1)
> {
> signal(SIGCHLD,SIG_DFL);
> }
> }
>
> int
> main(int argc, char *argv[])
> {
> int code;
> int pid;
> signal(SIGCHLD,&catch);
> pid = fork();
> if (pid == 0)
> {
> sleep(1);
> exit(0);
> }
> else
> {
> int pid2;
> int status;
> while (!pending)
> {
> struct timeval t;
> t.tv_usec = 100000;
> t.tv_sec = 0;
> code = select(0,NULL,NULL,NULL,&t);
> if (code && errno != EINTR)
> {
> perror("select");
> }
> }
> pid2 = wait(&status);
> fprintf(stderr,"wait pend=%d status=%d\n",pending,status);
> }
> }
--
___cliff rayman___cliff@genwax.com___http://www.genwax.com/
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