pthread_getspecific in signal handler

#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <sys/time.h>

#define N 4

sig_atomic_t signal_count[N];
pthread_key_t token;

long gettime ()
{
    struct timeval tv;
    gettimeofday (&tv, 0);
    return tv.tv_sec;
}

void idle_time(int seconds)
{
    long start = gettime();
    while(1)
    {
        if(gettime() > start + seconds)
        {
            break;
        }
    }
}

static void sigprof_handler(int sig_nr, siginfo_t* info, void *context)
{
    sig_atomic_t *counter = pthread_getspecific (token);
    if (counter)  *counter = *counter + 1;
}

void* thread_work(void* data)
{
    pthread_setspecific (token, data);

    // Do work
    idle_time (10);
    return NULL;
}

int main ()
{
    int i;
    for (i = 0; i < N; i++) signal_count[i] = 0;

    struct sigaction sa;
    sa.sa_sigaction = sigprof_handler;
    sa.sa_flags = SA_RESTART | SA_SIGINFO;
    sigemptyset(&sa.sa_mask);
    sigaction(SIGPROF, &sa, NULL);

    pthread_key_create (&token, NULL);

    static struct itimerval timer;
    timer.it_interval.tv_sec = 0;
    timer.it_interval.tv_usec = 1000000 / 1000; /* 1000hz */
    timer.it_value = timer.it_interval;
    setitimer(ITIMER_PROF, &timer, NULL);

    pthread_t threads[N];
    for(i = 0; i < N; i++)
    {
        pthread_create(&threads[i], NULL, thread_work, &(signal_count[i]));
    }

    for(i = 0; i < N; i++)
    {
        pthread_join(threads[i], NULL);
    }

    for(i = 0; i < N; i++)
    {
        printf("Signals caught after %dx10 seconds by thread %d: %ld \n", N, i, signal_count[i]);
    }

    pthread_key_delete (token);
}