Signal-based Scheduler

Makefile

CFLAGS = -g

all: sigsched
	./sigsched

clean:
	-rm -fr sigsched sigsched.dSYM

sigsched.c

#include <assert.h>
#include <signal.h>
#include <setjmp.h>
#include <stdlib.h>
#include <unistd.h>

static jmp_buf cont, stop;

static void handler(int sig)
{
	static int trigger;

	trigger = !trigger;
	alarm(3);

	if (trigger) {
		if (!setjmp(cont))
			longjmp(stop, 0);
	} else {
		if (!setjmp(stop))
			longjmp(cont, 0);
	}
}

void sigsched(void (*func)(void))
{
	signal(SIGALRM, handler);

	if (!setjmp(stop)) {
		assert(func);
		alarm(3);
		func();
		abort();
	}
}

static void foo(void)
{
	while (1) {
		static const char msg[] = "foo\n";

		write(1, msg, sizeof msg);
		sleep(1);
	}
}

static void bar(void)
{
	while (1) {
		static const char msg[] = "bar\n";

		write(1, msg, sizeof msg);
		sleep(1);
	}
}

int main(int argc, char *argv[])
{
	sigsched(foo);
	bar();
	abort();
	return 0;
}