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SubjectRe: ptrace(), fork(), sleep(), exit(), SIGCHLD
Have you receive off-line answers?
I guess that it's certainly more a strace issue and that it's perhaps
'trivial' for most people here. But I would be interesting in knowing the
why behind this.

Christophe

Le lun, 13 aoû 2001 10:29:32, Bruce Janson a écrit :
> Hi,
> The following program behaves incorrectly when traced:
>
> $ uname -a
> Linux dependo 2.4.2-2 #1 Sun Apr 8 19:37:14 EDT 2001 i686 unknown
> $ cc -v
> Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.96/specs
> gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-81)
> $ strace -V
> strace -- version 4.2
> $ cat t.c
> main()
> {
> switch (fork())
> {
> case -1:
> write(2, "fork\n", 5);
> break;
>
> case 0:
> usleep(1000000);
> break;
>
> default:
> if (usleep(5000000) == -1)
> write(2, "wrong\n", 6);
> break;
> }
>
> exit(0);
> }
> $ cc t.c
> $ time ./a.out
>
> real 0m5.011s
> user 0m0.000s
> sys 0m0.000s
> $ time strace -o /dev/null ./a.out
> wrong
>
> real 0m1.025s
> user 0m0.010s
> sys 0m0.010s
> $
>
> The problem appears to be that, when traced, the child process' exit()
> interrupts the parent's usleep() with a SIGCHLD, the latter returning
> EINTR.
> It also fails in the same way under Linux 2.2.16 and 2.2.19.
>
> What am I missing?
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--
Christophe Barbé
Software Engineer - christophe.barbe@lineo.fr
Lineo France - Lineo High Availability Group
42-46, rue Médéric - 92110 Clichy - France
phone (33).1.41.40.02.12 - fax (33).1.41.40.02.01
http://www.lineo.com
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