Hello!
There is a problem in fork(), in combination with kill(pid, 0)
to check if the child is alive:
When a fork() returned the pid to the parent, and the parent
does a kill(pid, 0) to check if the child is alive, the kill
sometimes return -1 and errno=ESRCH (No such process).
First i thought that fork() just returns before the child
has finished the fork. In the sample this seems to be true
for child 4, 1, and possibly 10.
But then i recognized that the child was already working,
but the parent's kill() still returns ESRCH. When the parent
does the kill a bit later, then it's ok. In the sample
this is the case for child 8, 5, 2 and 0.
I tested this with currently 1.3.6, 1.3.5, 1.1.8 and also
the snapshot-dll from 2002/01/08, but it's always the same.
Test program:
>8>8
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
int main(void)
{
int nChildPid = 0;
int nKillRv, nKillCnt;
int nCnt = 10;
int nRv = 0;
do {
nChildPid = fork();
switch(nChildPid) {
case -1:
perror("can't fork");
break;
case 0:
fprintf(stderr, "child: %d is up\n", nCnt);
sleep(2);
break;
default:
usleep(nCnt * 10);
nKillCnt = 2;
do {
fprintf(stderr, "parent: child %d", nCnt);
nKillRv = kill(nChildPid, 0);
if (nKillRv < 0) {
fprintf(stderr, " not found, %s\n",
strerror(errno));
++ nRv;
usleep(500000);
} else {
fprintf(stderr, " found\n");
}
} while(nKillRv < 0 && --nKillCnt >= 0);
sleep(1);
break;
}
} while(--nCnt >= 0 && nChildPid > 0);
return nRv;
}
8<8<
Output sample (not always the same):
>8>8
parent: child 10child: 10 is up
not found, No such process
parent: child 10 found
child: 9 is up
parent: child 9 found
child: 8 is up
parent: child 8 not found, No such process
parent: child 8 found
child: 7 is up
parent: child 7 found
child: 6 is up
parent: child 6 found
child: 5 is up
parent: child 5 not found, No such process
parent: child 5 found
parent: child 4 not found, No such process
child: 4 is up
parent: child 4 found
child: 3 is up
parent: child 3 found
child: 2 is up
parent: child 2 not found, No such process
parent: child 2 found
parent: child 1 not found, No such process
child: 1 is up
parent: child 1 found
child: 0 is up
parent: child 0 not found, No such process
parent: child 0 found
8<8<
Regards
haubi
--
Michael Haubenwallner SALOMON Automation GmbH
Forschung & Entwicklung A-8114 Friesach bei Graz
mailto:[EMAIL PROTECTED] http://www.salomon.at
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