EPOLL_WAIT(2)              Linux Programmer's Manual             EPOLL_WAIT(2)



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  indefi-
       nitely, 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.

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

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

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(4) epoll_create(2) epoll_ctl(2)




Linux                           23 October 2002                  EPOLL_WAIT(2)