epoll behaviour test on multriple threads environment

epoll-mt.c

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 
 * This program explains the following behaviour of epoll:
 * When multriple threads are waiting on same epoll instance simultaneously,
 * I/O event raised from a file registered on the epoll instance with edge
 * trigger mode cause exactly one thread to wake up; while with level trigger
 * mode cause at least one thread to wake up, depends on the event-consuming
 * time and the schedule of threads.
 *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 
 * Compile this file with -DUSE_EDGE_TRIGGER to see the behaviour of edge
 * trigger mode
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

#include <sys/epoll.h>
#include <sys/eventfd.h>
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

int epfd;
int evfd;

void *routine(void *param)
{
    printf ("thread %p ready\n", param);
    struct epoll_event epev;

    epoll_wait(epfd, &epev, 1, -1);
    eventfd_t result;
    usleep(1); // simulating some operation before we actually cosuming the event
    eventfd_read(evfd, &result);

    printf ("thread %p notified\n", param);

    return NULL;
}


int main()
{
    struct epoll_event epev;
    int i;
    epfd = epoll_create1(0);
    evfd = eventfd(0, EFD_NONBLOCK);

    epev.events = EPOLLIN;
#ifdef USE_EDGE_TRIGGER
    epev.events |= EPOLLET;
#endif
    epoll_ctl(epfd, EPOLL_CTL_ADD, evfd, &epev);

    pthread_t tid[100];

    for (i = 0; i < 100; ++i)
        pthread_create(tid + i, NULL, routine, tid + i);


    printf ("notifying\n");
    usleep(100);
    eventfd_write(evfd, 1);

    for (i = 0; i < 100; ++i)
        pthread_join(tid[i], NULL);

}