signalfd(2) alongside waitpid(2)

signalfd.c

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

#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static void	child(void);
static void	parent(void);
static void	fork_it(int);

static const int	nchilds = 3000;
static pid_t		childs[nchilds];

static void
child(void)
{
	ptrace(PTRACE_TRACEME, 0, 0, 0);
	raise(SIGSTOP);
	sleep(5);
}

static void
fork_it(int n)
{
	pid_t	pid;

	if (n == 0)
		return;

	switch ((pid = fork())) {
	case -1:
		err(1, "fork");
		break;
	case 0:
		child();
		_exit(0);
		break;
	default:
		childs[n - 1] = pid;
		fork_it(n - 1);
		break;
	}
}

static void
parent(void)
{
	sigset_t	mask;
	int		fd;

	sigemptyset(&mask);
	sigfillset(&mask);
	sigprocmask(SIG_SETMASK, &mask, NULL);

	if ((fd = signalfd(-1, &mask, 0)) == -1)
		err(1, "signalfd");

	while (1) {
		struct signalfd_siginfo	siginfo;
		ssize_t			n;

		n = read(fd, &siginfo, sizeof(siginfo));
		if (n != sizeof(siginfo))
			err(1, "read");

		printf("Got signal %d\n", siginfo.ssi_signo);
		switch (siginfo.ssi_signo) {
		case SIGINT:
		case SIGTERM:
			goto end;
			break;
		case SIGCHLD:
			{
				int	status;
				pid_t	pid;

				while (1) {
					pid = waitpid(-1, &status, WNOHANG);
					if (pid <= 0)
						break;

					if (WIFSTOPPED(status))
						ptrace(PTRACE_CONT, pid, 0, 0);
				}
			}
			break;
		}
	}

end:
	puts("Parent begins to shutdown");
	close(fd);
}

int
main(void)
{
	fork_it(nchilds);
	parent();

	/* Kill the children */
	{
		int	i;
		for (i = 0; i < nchilds; ++i)
			kill(childs[i], SIGKILL);
	}

	return (0);
}