Sending signals to threads with pthread_kill

signals.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <assert.h>
#include <signal.h>
#include <errno.h>

static pthread_t threads[2];
static int IDs[2] = { 1, 2 };
static int data, running, done;

static void signal_handler(int sig)
{
	data++;
}

static void *thread_func_2(void *args)
{
	int ID = *(int *)args;
	running = 1;

	while (!*(volatile int *)&done) {
		sleep(0);
	}

	printf("Thread %d: data = %d\n", ID, data);

	return NULL;
}

static void *thread_func_1(void *args)
{
	int i;

	// Make sure the other thread is up and running
	// pthread_kill may catch invalid thread IDs and return ESRCH,
	// but may just as well segfault
	// See http://udrepper.livejournal.com/16844.html
	while (!*(volatile int *)&running) ;

#define N 100

	// Send N signals
	for (i = 0; i < N; i++) {
		// Do something
		int fib = 0, f2 = 0, f1 = 1, j;
		for (j = 2; j <= 30; j++) {
			fib = f1 + f2; 
			f2 = f1;
			f1 = fib;
		}
		assert(pthread_kill(threads[1], SIGUSR1) == 0);
	}

	done = 1;
	
	return NULL;
}

int main(void)
{
	struct sigaction action;

	// Register signal handler
	action.sa_handler = signal_handler;
	action.sa_flags = SA_RESTART;
	sigaction(SIGUSR1, &action, NULL);

	pthread_create(&threads[0], NULL, thread_func_1, &IDs[0]);
	pthread_create(&threads[1], NULL, thread_func_2, &IDs[1]);

	pthread_join(threads[0], NULL);
	pthread_join(threads[1], NULL);

	return 0;
}