#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/wait.h>

#include <err.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>

static void
sighup(int sig __unused)
{
}

static void
sleep_forever(void)
{

	while (1)
		sleep(1);
}

static void *
thread(void *arg __unused)
{

	sleep_forever();
	return (NULL);
}

int
main(int argc, char **argv)
{
	struct sigaction act;
	sigset_t set;
	pthread_t t;
	pid_t pid, ret;
	int try, limit, status;

	pid = fork();
	if (pid < 0)
		err(1, "fork");
	if (pid == 0) {
		act.sa_handler = sighup;
		act.sa_flags = 0;
		sigemptyset(&act.sa_mask);
		if (sigaction(SIGHUP, &act, NULL) != 0)
			err(1, "sigaction");

		if (pthread_create(&t, NULL, thread, NULL) != 0)
			err(1, "pthread_create");

		/* Force SIGHUP to be delivered to the new thread. */
		sigemptyset(&set);
		sigaddset(&set, SIGHUP);
		if (pthread_sigmask(SIG_BLOCK, &set, NULL) != 0)
			err(1, "pthread_sigmask");

		sleep_forever();
	} else {
		sleep(1); /* give the child a chance to set itself up */

		limit = 100;
		for (try = 1; try <= limit; try++) {
			printf("attempt %d of %d\n", try, limit);
			if (kill(pid, SIGHUP) != 0)
				err(1, "kill(SIGHUP)");
			if (ptrace(PT_ATTACH, pid, NULL, 0) != 0)
				err(1, "ptrace(PT_ATTACH)");
			if (waitpid(pid, &status, WUNTRACED) != pid)
				err(1, "waitpid 1");
			if (!WIFSTOPPED(status))
				errx(1, "unexpected status %d after PT_ATTACH",
				    status);
			if (ptrace(PT_DETACH, pid, NULL, 0) != 0)
				err(1, "ptrace(PT_DETACH)");

			sleep(1);
			ret = waitpid(pid, &status, WUNTRACED | WNOHANG);
			if (ret < 0)
				err(1, "waitpid");
			if (ret == 0)
				continue;
			if (!WIFSTOPPED(status))
				errx(1, "unexpected status %d after PT_DETACH",
				    status);
			printf("stopped on signal %d after detach\n",
			    WSTOPSIG(status));
			sleep_forever();
		}
	}

	return (0);
}