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
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
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
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.
This page is part of release 3.14 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/.
