epoll_wait(2) -- Linux man page
NAME
epoll_wait - 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)
DESCRIPTION
Wait 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)
(EPOLL_CTL_ADD,EPOLL_CTL_MOD)
while the
events
member will contain the returned event bit field.
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.
- EINVAL
-
The supplied file descriptor,
epfd,
is not an
epoll
file descriptor, or the
maxevents
parameter is less than or equal to zero.
- EFAULT
-
The memory area pointed to by
events
is not accessible with write permissions.
CONFORMING TO
epoll_wait(2)
is a new API introduced in Linux kernel 2.5.44.
The interface should be finalized by Linux kernel 2.5.66.
SEE ALSO
epoll_ctl(2),
epoll_create(2),
epoll(4)
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