Manpage of EPOLL_CREATE

EPOLL_CREATE

Section: Linux Programmer's Manual (2)
Updated: 2015-12-28
Index
 

NAME

epoll_create, epoll_create1 - open an epoll file descriptor  

SYNOPSIS

#include <sys/epoll.h>int epoll_create(int size);int epoll_create1(int flags);
 

DESCRIPTION

epoll_create() creates an epoll(7) instance. Since Linux 2.6.8, the sizeargument is ignored, but must be greater than zero; see NOTES below.

epoll_create() returns a file descriptor referring to the new epoll instance. This file descriptor is used for all the subsequent calls to the epollinterface. 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 flagsis 0, then, other than the fact that the obsolete sizeargument is dropped, epoll_create1() is the same as epoll_create(). The following value can be included in flagsto obtain different behavior:
EPOLL_CLOEXEC
Set the close-on-exec (FD_CLOEXEC) flag on the new file descriptor. See the description of the O_CLOEXECflag in open(2) for reasons why this may be useful.
 

RETURN VALUE

On success, these system calls return a nonnegative file descriptor. On error, -1 is returned, and errnois set to indicate the error.  

ERRORS

EINVAL
sizeis not positive.
EINVAL
(epoll_create1()) Invalid value specified in flags.
EMFILE
The per-user limit on the number of epoll instances imposed by /proc/sys/fs/epoll/max_user_instanceswas encountered. See epoll(7) for further details.
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.
 

VERSIONS

epoll_create() was added to the kernel in version 2.6. Library support is provided in glibc starting with version 2.3.2.

epoll_create1() was added to the kernel in version 2.6.27. Library support is provided in glibc starting with version 2.9.  

CONFORMING TO

epoll_create() is Linux-specific.  

NOTES

In the initial epoll_create() implementation, the sizeargument informed the kernel of the number of file descriptors that the caller expected to add to the epollinstance. 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 sizemust still be greater than zero, in order to ensure backward compatibility when new epollapplications are run on older kernels.  

SEE ALSO

close(2), epoll_ctl(2), epoll_wait(2), epoll(7)


 

Index

NAME
SYNOPSIS
DESCRIPTION
epoll_create1()
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
NOTES
SEE ALSO

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