EPOLL_WAIT(2)		   Linux Programmers Manual		EPOLL_WAIT(2)



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

SYNOPSIS
       #include 

       int epoll_wait(int epfd, struct epoll_event *events,
		      int maxevents, int timeout);
       int epoll_pwait(int epfd, struct epoll_event *events,
		      int maxevents, int timeout,
		      const sigset_t *sigmask);

DESCRIPTION
       The epoll_wait() system	call  waits  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	avail
       able  for  the  caller.	 Up to maxevents are returned by epoll_wait().
       The maxevents argument must be greater than zero.  Specifying a timeout
       of  -1 makes epoll_wait() wait indefinitely, while specifying a timeout
       equal to zero makes epoll_wait()  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 an epoll_ctl(2) (EPOLL_CTL_ADD,EPOLL_CTL_MOD) while the events
       member will contain the returned event bit field.

   epoll_pwait()
       The relationship between epoll_wait() and epoll_pwait() is analogous to
       the  relationship  between  select(2)  and pselect(2): like pselect(2),
       epoll_pwait() allows an application to safely wait until either a  file
       descriptor becomes ready or until a signal is caught.

       The following epoll_pwait() call:

	   ready = epoll_pwait(epfd, &events, maxevents, timeout, &sigmask);

       is equivalent to atomically executing the following calls:

	   sigset_t origmask;

	   sigprocmask(SIG_SETMASK, &sigmask, &origmask);
	   ready = epoll_wait(epfd, &events, maxevents, timeout);
	   sigprocmask(SIG_SETMASK, &origmask, NULL);

       The   sigmask  argument	may  be  specified  as	NULL,  in  which  case
       epoll_pwait() is equivalent to epoll_wait().

RETURN VALUE
       When successful, epoll_wait() 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() 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; see signal(7).

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

VERSIONS
       epoll_pwait() was added to Linux in kernel 2.6.19.

       Glibc  support for epoll_pwait() is provided starting with version 2.6.

CONFORMING TO
       epoll_wait() is Linux-specific, and was introduced in kernel 2.5.44.

SEE ALSO
       epoll_create(2), epoll_ctl(2), epoll(7)

COLOPHON
       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux				  2008-04-23			 EPOLL_WAIT(2)