waitpid == -1 and errno == ECHILD
alexandrug
Suppose I have this code :
{
pid = fork();
int exitcode = 0;
if (pid == 0) { do_some_actions(); }
if ( waitpid(pid, &exitcode,0) == -1)
{
switch(errno) {
case ECHILD: do_something();
break;
case EINTR: break;
default : break;
}
}
In what conditions we can have waitpid == -1 and errno == ECHILD,
supposing that the signal handler for SIGCHLD is NOT SIG_IGN ?
Thank you,
Alexandru.
Eric Sosman
In what you've shown, the waitpid() call executes in both
the parent and the child processes. In the child, it tries to
wait for pid zero -- that is, for any of the child's own children.
If the child has no children of its own, ECHILD is correct.
If that's not the problem with your actual code -- well,
I'm not a mind reader, and I can't debug what I can't see.
--
Eric Sosman
eso...@ieee-dot-org.invalid
alexandrug
More precisely, the code is like this :
{
pid = fork();
int exitcode = 0;
if (pid == 0) while(1) { do_some_actions(); }
// only in parent process
Alan Curry
alexandrug <weba...@gmail.com> wrote:
>> > In what conditions we can have waitpid == -1 and errno == ECHILD,
>> > supposing that the signal handler for SIGCHLD is NOT SIG_IGN ?
>
>
>{
>pid = fork();
>int exitcode = 0;
>
>if (pid == 0) while(1) { do_some_actions(); }
>
>// only in parent process
>
>if ( waitpid(pid, &exitcode,0) == -1)
>{
>switch(errno) {
>case ECHILD: do_something();
> break;
>case EINTR: break;
>default : break;
>
>}
>}
It could happen if pid==(pid_t)-1 i.e. fork failed, which you didn't check
for.
--
Alan Curry
Jiří Paleček
> Greetings,
Hello,
waitpid() exeuted in the parent can fail with ECHILD eg. if there is a
handler for SIGCHLD and it calls wait*() function, or if another thread
calls wait() simultaneously. IMHO the best way to inspect this is run the
program under strace.
Regards
Jiri Palecek
alexandrug
> In article <e22036c1-e514-430d-b372-93681ff25...@m3g2000yqf.googlegroups.com>,
>
>
>
> alexandrug <webaig...@gmail.com> wrote:
> >> > In what conditions we can have waitpid == -1 and errno == ECHILD,
> >> > supposing that the signal handler for SIGCHLD is NOT SIG_IGN ?
>
> >More precisely, the code is like this :
>
> >{
> >pid = fork();
> >int exitcode = 0;
>
> >if (pid == 0) while(1) { do_some_actions(); }
>
> >// only in parent process
>
> >if ( waitpid(pid, &exitcode,0) == -1)
> >{
> >switch(errno) {
> >case ECHILD: do_something();
> > break;
> >case EINTR: break;
> >default : break;
>
> >}
> >}
>
> It could happen if pid==(pid_t)-1 i.e. fork failed, which you didn't check
> for.
>
> --
> Alan Curry
Suppose that
1) pid = fork() > 0, in parent process (ie, fork() was successful)
2) there is NOT any handler for SIGCHLD, that colls wait*()
3) there is NOT any thread which calls wait*()
4) the signal handler for SIGCHLD is set, but NOT to SIG_IGN
5) at runtime, we have waitpid(pid, &exitcode, 0) == -1
In what conditions we could have errno == ECHILD ? (*)
I noticed that if I kill -9 (manually) the child process, then
the child process (defunct) will still exist in the process table,
and a waitpid() on it would return a code of success.
Please help me with my question : (*).
Thanks,
Alexandru.
Alan Curry
alexandrug <weba...@gmail.com> wrote:
>On Nov 28, 12:59�am, pac...@kosh.dhis.org (Alan Curry) wrote:
>
>Suppose that
>
>1) pid = fork() > 0, in parent process (ie, fork() was successful)
>2) there is NOT any handler for SIGCHLD, that colls wait*()
>3) there is NOT any thread which calls wait*()
>4) the signal handler for SIGCHLD is set, but NOT to SIG_IGN
>
>5) at runtime, we have waitpid(pid, &exitcode, 0) == -1
>
>In what conditions we could have errno == ECHILD ? (*)
Let's just say it's a kernel bug. If it's reproducable, write a minimal test
program that demonstrates it, put a system("ps axj") after the errno==ECHILD
test, and follow your vendor's bug reporting procedure.
--
Alan Curry