From: Stefan Sperling <stsp@stsp.name>
Subject: Re: responsive watch wip
To: Ted Unangst <tedu@tedunangst.com>
Cc: tech@openbsd.org
Date: Wed, 11 Jun 2025 10:15:47 +0200

On Mon, Jun 09, 2025 at 11:28:35PM -0400, Ted Unangst wrote:
> We might lose track of which child exited? Not sure how much this
> matters. This is where I would use kevent, because I don't know how
> to get the exiting pid out of libevent.

It is possible to register signal handlers via libevent.
Such signals will appear as EV_SIGNAL events in the event loop. 

If you catch SIGCHLD this way then you can get the pid from waitpid().

For example, exiting children in gotd are caught like this:

void
gotd_sighdlr(int sig, short event, void *arg)
{
[...]
	switch (sig) {
[...]
	case SIGCHLD:
		for (;;) {
			pid = waitpid(WAIT_ANY, &status, WNOHANG);
[...]

int
main(int argc, char **argv)
{
	struct event evsigchld;
[...]
	signal_set(&evsigchld, SIGCHLD, gotd_sighdlr, NULL);
	signal_add(&evsigchld, NULL);