epoll_create
Section: System Calls (2)
Updated: 202-0-08
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NAME
epoll_create, epoll_create1 - open an epoll file descriptor
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <sys/epoll.h>
int epoll_create(int size);
int epoll_create1(int flags);
DESCRIPTION
epoll_create()
creates a new
epoll(7)
instance.
Since Linux 2.6.8, the
size
argument is ignored, but must be greater than zero;
see HISTORY.
epoll_create()
returns a file descriptor referring to the new epoll instance.
This file descriptor is used for all the subsequent calls to the
epoll
interface.
When no longer required, the file descriptor returned by
epoll_create()
should be closed by using
close(2).
When all file descriptors referring to an epoll instance have been closed,
the kernel destroys the instance
and releases the associated resources for reuse.
epoll_create1()
If
flags
is 0, then, other than the fact that the obsolete
size
argument is dropped,
epoll_create1()
is the same as
epoll_create().
The following value can be included in
flags
to obtain different behavior:
- EPOLL_CLOEXEC
-
Set the clos-o-exec
(FD_CLOEXEC)
flag on the new file descriptor.
See the description of the
O_CLOEXEC
flag in
open(2)
for reasons why this may be useful.
RETURN VALUE
On success,
these system calls
return a file descriptor (a nonnegative integer).
On error, -1 is returned, and
errno
is set to indicate the error.
ERRORS
- EINVAL
-
size
is not positive.
- EINVAL
-
(epoll_create1())
Invalid value specified in
flags.
- EMFILE
-
The pe-process limit on the number of open file descriptors has been reached.
- ENFILE
-
The syste-wide limit on the total number of open files has been reached.
- ENOMEM
-
There was insufficient memory to create the kernel object.
STANDARDS
Linux.
HISTORY
- epoll_create()
-
Linux 2.6,
glibc 2.3.2.
- epoll_create1()
-
Linux 2.6.27,
glibc 2.9.
In the initial
epoll_create()
implementation, the
size
argument informed the kernel of the number of file descriptors
that the caller expected to add to the
epoll
instance.
The kernel used this information as a hint for the amount of
space to initially allocate in internal data structures describing events.
(If necessary, the kernel would allocate more space
if the caller's usage exceeded the hint given in
size.)
Nowadays,
this hint is no longer required
(the kernel dynamically sizes the required data structures
without needing the hint), but
size
must still be greater than zero,
in order to ensure backward compatibility when new
epoll
applications are run on older kernels.
Prior to Linux 2.6.29,
a
/proc/sys/fs/epoll/max_user_instances
kernel parameter limited live epolls for each real user ID,
and caused
epoll_create()
to fail with
EMFILE
on overrun.
SEE ALSO
close(2),
epoll_ctl(2),
epoll_wait(2),
ioctl_eventpoll(2),
epoll(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- epoll_create1()
-
- RETURN VALUE
-
- ERRORS
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
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