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.\"
.\" epoll by Davide Libenzi ( efficient event notification retrieval )
.\" Copyright (C) 2003 Davide Libenzi
.\"
.\" This program is free software; you can redistribute it and/or modify
.\" it under the terms of the GNU General Public License as published by
.\" the Free Software Foundation; either version 2 of the License, or
.\" (at your option) any later version.
.\"
.\" This program is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public License
.\" along with this program; if not, write to the Free Software
.\" Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
.\"
.\" Davide Libenzi <davidel@xmailserver.org>
.\"
.\" 2007-04-30: mtk, Added description of epoll_pwait()
.\"
.TH EPOLL_WAIT 2 2009-01-17 "Linux" "Linux Programmer's Manual"
.SH NAME
epoll_wait, epoll_pwait \- wait for an I/O event on an epoll file descriptor
.SH SYNOPSIS
.nf
.B #include <sys/epoll.h>
.sp
.BI "int epoll_wait(int " epfd ", struct epoll_event *" events ,
.BI " int " maxevents ", int " timeout );
.BI "int epoll_pwait(int " epfd ", struct epoll_event *" events ,
.BI " int " maxevents ", int " timeout ,
.BI " const sigset_t *" sigmask );
.fi
.SH DESCRIPTION
The
.BR epoll_wait ()
system call waits for events on the
.B epoll
instance referred to by the file descriptor
.IR epfd .
The memory area pointed to by
.I events
will contain the events that will be available for the caller.
Up to
.I maxevents
are returned by
.BR epoll_wait ().
The
.I maxevents
argument must be greater than zero.
The call waits for a maximum time of
.I timeout
milliseconds.
Specifying a
.I timeout
of \-1 makes
.BR epoll_wait ()
wait indefinitely, while specifying a
.I timeout
equal to zero makes
.BR epoll_wait ()
to return immediately even if no events are available
(return code equal to zero).
The
.I struct epoll_event
is defined as :
.sp
.in +4n
.nf
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 */
};
.fi
.in
The
.I data
of each returned structure will contain the same data the user set with an
.BR epoll_ctl (2)
.RB ( EPOLL_CTL_ADD , EPOLL_CTL_MOD )
while the
.I events
member will contain the returned event bit field.
.SS epoll_pwait()
The relationship between
.BR epoll_wait ()
and
.BR epoll_pwait ()
is analogous to the relationship between
.BR select (2)
and
.BR pselect (2):
like
.BR pselect (2),
.BR epoll_pwait ()
allows an application to safely wait until either a file descriptor
becomes ready or until a signal is caught.
The following
.BR epoll_pwait ()
call:
.nf
ready = epoll_pwait(epfd, &events, maxevents, timeout, &sigmask);
.fi
is equivalent to
.I atomically
executing the following calls:
.nf
sigset_t origmask;
sigprocmask(SIG_SETMASK, &sigmask, &origmask);
ready = epoll_wait(epfd, &events, maxevents, timeout);
sigprocmask(SIG_SETMASK, &origmask, NULL);
.fi
.PP
The
.I sigmask
argument may be specified as NULL, in which case
.BR epoll_pwait ()
is equivalent to
.BR epoll_wait ().
.SH "RETURN VALUE"
When successful,
.BR 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
.I timeout
milliseconds.
When an error occurs,
.BR epoll_wait ()
returns \-1 and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EBADF
.I epfd
is not a valid file descriptor.
.TP
.B EFAULT
The memory area pointed to by
.I events
is not accessible with write permissions.
.TP
.B EINTR
The call was interrupted by a signal handler before any of the
requested events occurred or the
.I timeout
expired; see
.BR signal (7).
.TP
.B EINVAL
.I epfd
is not an
.B epoll
file descriptor, or
.I maxevents
is less than or equal to zero.
.SH VERSIONS
.BR epoll_pwait ()
was added to Linux in kernel 2.6.19.
Glibc support for
.BR epoll_pwait ()
is provided starting with version 2.6.
.SH CONFORMING TO
.BR epoll_wait ()
is Linux-specific, and was introduced in kernel 2.5.44.
.\" The interface should be finalized by Linux kernel 2.5.66.
.SH "SEE ALSO"
.BR epoll_create (2),
.BR epoll_ctl (2),
.BR epoll (7)
.SH COLOPHON
This page is part of release 3.27 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
|
