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NAME

       epoll_wait - wait for an I/O event on an epoll file descriptor

SYNOPSIS

       #include <sys/epoll.h>

       int  epoll_wait(int  epfd,  struct epoll_event * events, int maxevents,
       int timeout)

DESCRIPTION

       Wait for events on the epoll file descriptor epfd for a maximum time of
       timeout milliseconds. The memory area pointed to by events will contain
       the events that will be available for the caller.  Up to maxevents  are
       returned  by  epoll_wait(2).   The  maxevents parameter must be greater
       than  zero.  Specifying  a  timeout  of  -1  makes  epoll_wait(2)  wait
       indefinitely,   while   specifying   a  timeout  equal  to  zero  makes
       epoll_wait(2) to return immediately even if no events are  available  (
       return code equal to zero ).  The struct epoll_event is defined as :

            typedef union epoll_data {
                 void *ptr;
                 int fd;
                 __uint32_t u32;
                 __uint64_t u64;
            } epoll_data_t;

            struct epoll_event {
                 __uint32_t events;  /* Epoll events */
                 epoll_data_t data;  /* User data variable */
            };

       The data of each returned structure will contain the same data the user
       set with a epoll_ctl(2) (EPOLL_CTL_ADD,EPOLL_CTL_MOD) while the  events
       member will contain the returned event bit field.

RETURN VALUE

       When  successful,  epoll_wait(2) returns the number of file descriptors
       ready for the requested I/O, or zero if no file descriptor became ready
       during  the  requested  timeout  milliseconds.   When  an error occurs,
       epoll_wait(2) returns -1 and errno is set appropriately.

ERRORS

       EBADF  epfd is not a valid file descriptor.

       EFAULT The memory area pointed to by  events  is  not  accessible  with
              write permissions.

       EINTR  The  call  was interrupted by a signal handler before any of the
              requested events occurred or the timeout expired.

       EINVAL epfd is not an epoll file descriptor, or maxevents is less  than
              or equal to zero.

CONFORMING TO

       epoll_wait(2)  is  a  new  API  introduced in Linux kernel 2.5.44.  The
       interface should be finalized by Linux kernel 2.5.66.

SEE ALSO

       epoll_create(2), epoll_ctl(2), epoll(4)