epoll_wait

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	 max-
       events 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.

       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_ctl(2), epoll_create(2), epoll(4)




Linux			       23 October 2002			EPOLL_WAIT(2)