#include <sys/atomic.h>
#include <sys/wait.h>

#include <assert.h>
#include <err.h>
#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>

volatile unsigned lock = 0;
__thread unsigned locks = 0;
__thread sigset_t sigmask;
sigset_t sigset_all;

static void
clearSignalHandlers(void)
{
	unsigned i;

	for (i = 0; i < _NSIG; i++) {
		struct sigaction sa;
		memset(&sa, 0, sizeof(sa));
		sa.sa_flags = SA_SIGINFO|SA_ONSTACK|SA_RESTART;
		sa.sa_mask = sigset_all;
		sa.sa_sigaction = (void (*)(int, siginfo_t *, void *))SIG_DFL;
		sigaction(i, &sa, NULL); /* XXX _cgo_sigaction? */
	}
}

static void *
start(void *cookie)
{
	pid_t pid;

	for (;;) {
		locks++;
		sigprocmask(SIG_SETMASK, NULL, &sigmask); /* sigsave */
		sigprocmask(SIG_SETMASK, &sigset_all, NULL); /* sigblock */
		pid = fork();
		switch (pid) {
		case -1:	/* error */
			err(1, "fork");
		case 0:		/* child */
			clearSignalHandlers();
			sigprocmask(SIG_SETMASK, &sigmask, NULL); /* msigrestore */
			_exit(0);
		default:	/* parent */
			break;
		}
		sigprocmask(SIG_SETMASK, &sigmask, NULL); /* msigrestore */
		if (--locks)
			errx(1, "lock count");
		if (wait4(pid, NULL, 0, NULL) == -1)
			err(1, "wait4");
	}
}

int
main(void)
{
	pthread_t t;
	unsigned n = 100;
	int error;

	sigfillset(&sigset_all);

	while (n --> 0) {
		error = pthread_create(&t, NULL, &start, NULL);
		if (error)
			errc(1, error, "pthread_create");
	}

	(void)pthread_join(t, NULL);
	return 0;
}