epoll_create(2) System Calls Manual epoll_create(2)
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 in-
stance. This file descriptor is used for all the subsequent calls to
the epoll interface. When no longer required, the file descriptor re-
turned 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 argu-
ment 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 close-on-exec (FD_CLOEXEC) flag on the new file descrip-
tor. 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 per-process limit on the number of open file descriptors has
been reached.
ENFILE The system-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 in-
formed the kernel of the number of file descriptors that the caller ex-
pected 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 al-
locate more space if the caller's usage exceeded the hint given in
size.) Nowadays, this hint is no longer required (the kernel dynami-
cally sizes the required data structures without needing the hint), but
size must still be greater than zero, in order to ensure backward com-
patibility 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), epoll(7)
Linux man-pages 6.7 2023-10-31 epoll_create(2)
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