epoll_wait, epoll_pwait — wait for an I/O event on an epoll file descriptor
#include <sys/epoll.h>
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); |
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 available for the caller. Up to maxevents are returned by
epoll_wait(). The maxevents parameter 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_data_t data;};
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.
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);
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.
epfd is not
a valid file descriptor.
The memory area pointed to by events is not accessible
with write permissions.
The call was interrupted by a signal handler before
any of the requested events occurred or the timeout expired.
epfd is not
an epoll file
descriptor, or maxevents is less than or
equal to zero.
epoll_pwait() was added to
Linux in kernel 2.6.19.
Glibc support for epoll_pwait() is provided starting with
version 2.6.
This page is part of release 2.79 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/.
|
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 <davidelxmailserver.org> 2007-04-30: mtk, Added description of epoll_pwait() |