NAME
epoll_wait, epoll_pwait - wait for an I/O event on an epoll file descriptor
SYNOPSIS
#include <sys/epoll.h>
I int epoll_wait(int epfd , struct epoll_event * events ,
I int maxevents , int timeout );
I int epoll_pwait(int epfd , struct epoll_event * events ,
I int maxevents , int timeout ,
I const sigset_t * sigmask );
DESCRIPTION
The
R 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(2).
The
maxevents
parameter must be greater than zero.
Specifying a
timeout
of -1 makes
epoll_wait(2)
wait indefinitely, while specifying a
timeout
equal to zero makes
epoll_wait(2)
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 a
epoll_ctl(2)
R ( EPOLL_CTL_ADD , EPOLL_CTL_MOD )
while the
events
member will contain the returned event bit field.
epoll_pwait()
The relationship between
R epoll_wait ()
and
R epoll_pwait ()
is analogous to the relationship between
select(2)
and
pselect(2):
like
pselect(2),
R epoll_pwait ()
allows an application to safely wait until either a file descriptor
becomes ready or until a signal is caught.
The following
R 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);
RETURN VALUE
When successful,
epoll_wait(2)
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(2)
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.
EINVAL
R epfd
is not an
epoll
file descriptor, or
maxevents
is less than or equal to zero.
VERSIONS
R epoll_pwait ()
was added to Linux in kernel 2.6.19.
Glibc support for
R epoll_pwait ()
is provided starting with version 2.6.
CONFORMING TO
epoll_wait(2)
is Linux specific, and was introduced in kernel 2.5.44.
SEE ALSO
ČLÁNKY DO MAILU