I think you might be taking this personally. Please don't. I'd
really like a productive dialog here. Perhaps we're talking past each
other. Perhaps we're not looking at the same version of libev. (I'm
looking at 2.01.) Perhaps I'm an idiot. However, even if I'm an
idiot, I'm not attacking you. A little politeness doesn't cost you
much.
On Mon, Jan 14, 2008 at 03:06:41AM +0100, Marc Lehmann wrote:
On Sun, Jan 13, 2008 at 06:05:18PM -0500, Chris Shoemaker [EMAIL PROTECTED]
wrote:
As I explained, if for whatever reason it is inconvinient to use it,
don't. Libev doesn't force the use of its child watcher.
Well, it doesn't force the use of ev_child, but it does force an
application to choose between either:
a) not having access to the exit status of children that exited before a
ev_child was started, OR
As I said earlier, this is untrue. Why do you kepe repeating it? libev
*explicitly* allows registering an ev_child handler after the child has
exited already, anythign else would be pointless indeed.
I will try to be more explicit about why I believe that this doesn't work.
This is actually used in practise, so if it doesn't work, I'd like to know
why.
I will also try to explain why it doesn't work.
b) not being able to use ev_signal
That is also untrue. Nothing precludes libev users form using ev_signal
but install their own sigchld handler, as was explained before.
I guess I've failed to effectively communicate the problem, so I will
try some different approaches.
I'd like to use ev_signal (for unrelated purposes, mostly) AND have access
to exit status of children that exited before I knew I would want their
exit status, (for which I know I need to use my old SIGCHLD handler, that
I used with libevent).
I will never understand how people can know factually wrong things.
You made this claim repeatedly, please back it up, or take it back. Thanks.
Okay. I guess the simplest proof is in the code:
ev.c has a childcb SIGCHLD handler containing:
if (0 = (pid = waitpid (-1, status, WNOHANG | WUNTRACED | WCONTINUED)))
if (!WCONTINUED
|| errno != EINVAL
|| 0 = (pid = waitpid (-1, status, WNOHANG | WUNTRACED)))
return;
...
child_reap (EV_A_ sw, pid, pid, status);
Notice that nothing prevents the waitpid from reaping any child at all.
child_reap() contains:
for (w = (ev_child *)childs [chain (EV_PID_HASHSIZE - 1)]; w; w = (ev_child
*)((WL)w)-next)
if (w-pid == pid || !w-pid)
{
... [ feed the event ]
}
Notice that if the conditional (w-pid == pid || !w-pid) is false for all
ev_childs, then
a) we have just reaped a child, and have its status.
b) we will not be generating any event, since no ev_child matches.
c) we will never again see the status for this child
All that is then required is for someone to start a ev_child for the
child we just reaped. That event will never trigger.
If you'd prefer a more empirical approach, you can run this program:
*
#include ev.h
#include stdio.h
#include unistd.h
#include signal.h
#include stdlib.h
#include sys/wait.h
struct ev_child child_watcher;
struct ev_signal signal_watcher;
static void signal_cb (EV_P_ struct ev_signal *w, int revents) {
printf (signal\n);
ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
}
static void cb (EV_P_ struct ev_child *w, int revents) {
printf (w-pid = %d; w-rstatus = %d\n, w-rpid, WEXITSTATUS(w-rstatus));
ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
}
int main (int args, char *argv[]) {
struct ev_loop *loop = ev_default_loop(0/*EV_FORK_ENABLE*/);
pid_t pid;
ev_signal_init (signal_watcher, signal_cb, SIGHUP);
ev_signal_start (loop, signal_watcher);
if ((pid = fork()) == 0) {
exit(99);
}
printf(spawned %d\n, pid);
if (fork() == 0) {
sleep(5);
kill(pid, SIGHUP);
exit(98);
}
ev_loop(loop, EVLOOP_NONBLOCK);
sleep(1);
printf(STARTING LOOP %d\n, pid);
ev_child_init (child_watcher, cb, pid);
ev_child_start (loop, child_watcher);
ev_loop(loop, 0);
printf(done\n);
return 0;
}
If I understand what you're claiming, then that program should print the
exit status 99, and then terminate. In fact, it does neither.
An strace of the process shows why, and it agrees with the source code:
...
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x2aac7770) = 21046
--- SIGCHLD (Child exited) @ 0 (0) ---
write(4, \21, 1) = 1
write(1, spawned 21046\n, 14) = 14
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x2aac7770) = 21047
epoll_ctl(5, EPOLL_CTL_ADD, 3, {EPOLLIN, {u32=3, u64=3}}) = 0
epoll_wait(5, {{EPOLLIN, {u32=3, u64=3}}}, 64, 0) = 1
read(3, \21, 1) = 1
wait4(-1, [{WIFEXITED(s) WEXITSTATUS(s) == 99}],
WNOHANG|WSTOPPED|WCONTINUED, NULL) = 21046
wait4(-1, 0x7fffd639771c,
