thread start/stop

#define _GNU_SOURCE

#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <pthread.h>

pthread_t tid[2];
pthread_mutex_t startlock;
pthread_cond_t startcond;

#define START   1
#define STOP    2

static void usr2 (int signum, siginfo_t *siginfo, void *context)
{
    sigset_t intmask;

    printf("T [%lu]: got signal%d\n", pthread_self(), signum);
    sigemptyset(&intmask);
    sigaddset(&intmask, signum);
    sigprocmask(SIG_UNBLOCK, &intmask, NULL);

    if(siginfo->si_value.sival_int == STOP) {
        pthread_mutex_init(&startlock, NULL);
        pthread_cond_init(&startcond, NULL);
        pthread_mutex_lock(&startlock);
        pthread_cond_wait(&startcond, &startlock);
        pthread_mutex_unlock(&startlock);
    } else if(siginfo->si_value.sival_int == START) {
        pthread_cond_signal(&startcond);
    } else
        printf("unknown action: %d\n", siginfo->si_value.sival_int);
}

static void * t1(void *arg)
{
    for(int i = 0; ; i++) {
        printf("T1[%lu]: %d\n", pthread_self(), i);
        sleep(1);
    }

    return NULL;
}

static void * t2(void *arg)
{
    for(int i = 0; ; i++) {
        printf("T2[%lu]: %d\n", pthread_self(), i);
        sleep(1);
        if(i == 1) {
            printf("T2[%lu]: sending signal STOP\n", pthread_self());
            pthread_sigqueue(tid[0], SIGUSR2, (union sigval)STOP);
        } else if(i == 5) {
            printf("T2[%lu]: sending signal START\n", pthread_self());
            pthread_sigqueue(tid[0], SIGUSR2, (union sigval)START);
        } else if(i == 8) {
            printf("T2[%lu]: sending signal RANDOM\n", pthread_self());
            pthread_sigqueue(tid[0], SIGUSR2, (union sigval)(int)(tid[0] * tid[1] >> 16 & 0xffff));
        }
    }

    return NULL;
}

struct sigaction act = {
    .sa_sigaction = usr2,
    .sa_flags = SA_SIGINFO,
};

int main(int argc, char *argv[])
{
    sigaction(SIGUSR2, &act, NULL);

    pthread_create(tid + 0, NULL, t1, 0);
    pthread_create(tid + 1, NULL, t2, 0);

    while(1)
        sleep(10);
    return 0;
}