io_uring_eventfd_not_work.c

#include <sys/eventfd.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <liburing.h>
#include <fcntl.h>
#include <poll.h>
#include <sys/time.h>

struct io_uring ring;

void error_exit(char *message) {
    perror(message);
    exit(EXIT_FAILURE);
}

void *listener_thread(void *data) {
    struct io_uring_cqe *cqe;
    printf("%s: Waiting for completion event...\n", __FUNCTION__);

    for(;;) {
        int ret = io_uring_wait_cqe(&ring, &cqe);
        if (ret < 0) {
            fprintf(stderr, "Error waiting for completion: %s\n",
                strerror(-ret));
            return NULL;
        }
        if (cqe->res < 0) {
            fprintf(stderr, "Error in async operation: %s\n", strerror(-cqe->res));
        }
        printf("Result of the operation: %d\n", cqe->res);
        printf("Result: data: %lld \n", cqe->user_data);
        io_uring_cqe_seen(&ring, cqe);
        
    }
    return NULL;
}

void *wakeup_io_uring(void *data) {
    int efd = (int) data;
    printf("efd: %d\n", efd);
 
    int res = eventfd_write(efd, (eventfd_t) 1L);
    printf("Write eventfd res: %d \n", res);

    return NULL;
}

int setup_io_uring(int efd) {
    int ret = io_uring_queue_init(8, &ring, 0);
    if (ret) {
        fprintf(stderr, "Unable to setup io_uring: %s\n", strerror(-ret));
        return 1;
    }
    return 0;
}

int main() {
    pthread_t t1;
    pthread_t t2;
    int efd;
    struct io_uring_sqe *sqe;

    efd = eventfd(0, 0);
    if (efd < 0) {
        error_exit("eventfd");
    }
    printf("Efd: %d \n", efd);

    setup_io_uring(efd);

    pthread_create(&t1, NULL, listener_thread, NULL);

    sqe = io_uring_get_sqe(&ring);
    io_uring_prep_poll_add(sqe, efd, POLLIN);
    sqe->user_data = 2;
    int ret = io_uring_submit(&ring);
    printf("Submit Result: %d\n", ret);

    sleep(1);

    //io_uring_enter will get a polling event if you move eventfd_write(efd, (eventfd_t) 1L) to the main thread or the other way around
    pthread_create(&t2, NULL, wakeup_io_uring, (void *)efd);
    
    pthread_join(t1, NULL);

    io_uring_queue_exit(&ring);
    return EXIT_SUCCESS;
}