EPOLL_WAIT
Section: Linux Programmer's Manual (2)
Updated: 2009-01-17
NAME
epoll_wait, epoll_pwait - 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);
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
instance referred to by the file descriptor
epfd.
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
argument must be greater than zero.
The call waits for a maximum time of
timeout
milliseconds.
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 3.27 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- epoll_pwait()
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- SEE ALSO
-
- COLOPHON
-
This document was created by
man2html,
using the manual pages.
Time: 07:34:55 GMT, March 26, 2013