通过eventfd在线程之间传输数据

我想通过eventfd在线程之间传输数据 . 所以我写下面的代码来满足我的需要 . 我的主机操作系统是openSUSE v12.3 64bit .

#include "stdio.h"
 #include "unistd.h"
 #include "pthread.h"
 #include "sys/eventfd.h"
 #include "sys/epoll.h"
 #define nil NULL

 int efd = -1;

 void* read_thread(void* arg)   {

        int ret = 0;
    uint64_t count = 0;
    int ep_fd = -1;
    struct epoll_event events[10];

    (void)(arg);
    if (efd < 0) {
        printf("efd not inited.\n");
        return nil;
    }

    ep_fd = epoll_create(1024);
    if (ep_fd < 0) {
        perror("epoll_create fail: ");
        return nil;
    }

    {
        struct epoll_event read_event;

        read_event.events = EPOLLIN;
        read_event.data.fd = efd;

        ret = epoll_ctl(ep_fd, EPOLL_CTL_ADD, efd, &read_event);
        if (ret < 0) {
            perror("epoll ctl failed:");
            return nil;
        }
    }

    while (1) {
        ret = epoll_wait(ep_fd, events, 10, 5000);
        if (ret > 0) {
            int i = 0;
            for (i = 0; i < ret; i++) {
                if (events[i].events & (EPOLLHUP | EPOLLERR)) {
                    printf("epoll eventfd has epoll hup.\n");
                    break;
                } else if (events[i].events & EPOLLIN) {
                    int event_fd = events[i].data.fd;
                    ret = eventfd_read(event_fd, &count);
                    if (ret < 0) {
                        perror("read fail:");
                        break;
                    } else {
                        printf("read %llu\n", count);
                    }
                }
            }
        } else if (ret == 0) {
            break;
        } else {
            perror("epoll wait error:");
            break;
        }
    }

    close(ep_fd);
    return nil;
}

int main(int argc, char *argv[]) {

    pthread_t pid = 0;
    uint64_t count = 0;
    int ret = 0;
    int i = 0;

    efd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
    if (efd < 0) {
        perror("eventfd failed.");
        return -1;
    }

    ret = pthread_create(&pid, NULL, read_thread, NULL);
    if (ret < 0) {
        perror("pthread create:");
        close(efd);
        return -2;
    }

    for (i = 0; i < 5; i++) {
        count = i + 1;
        ret = eventfd_write(efd, count);
        if (ret < 0) {
            perror("write event fd fail:");
            break;
        } else {
            printf("write %llu\n", count);
        }
    }

    sleep(3);

    pthread_join(pid, NULL);
    close(efd);
    efd = -1;

    return 0;
}

我认为eventfd的行为应该像管道一样 . 所以程序的输出结果可能如下：

写1读1写2读2写3读3写4读4写5读5

但是，它的实际结果是：

写1写2写3写4写5读15

要么

写1写2写3写4写5读1读14

有些好人可以告诉我为什么输出结果是输入结果的总和？

我无法通过线程之间的eventfd正确传输数据 . 我也不喜欢烟斗 . 如何在线程之间正确地传输数据？