EPOLL_CREATE(2) Linux Programmer's Manual EPOLL_CREATE(2)
epoll_create, epoll_create1 - open an epoll file descriptor
int epoll_create(int size);
int epoll_create1(int flags);
epoll_create() creates an epoll(7) instance. Since Linux 2.6.8, the size argument 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 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.
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:
Set the close-on-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.
On success, these system calls return a nonnegative file descriptor. On error, -1 is
returned, and errno is set to indicate the error.
EINVAL size is 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_instances was encountered. See epoll(7) for further
ENFILE The system limit on the total number of open files has been reached.
ENOMEM There was insufficient memory to create the kernel object.
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.
epoll_create() is Linux-specific.
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 compati-
bility when new epoll applications are run on older kernels.
close(2), epoll_ctl(2), epoll_wait(2), epoll(7)
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Linux 2012-04-15 EPOLL_CREATE(2)