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 a new epoll(7) instance. Since Linux 2.6.8, the
size argument is ignored, but must be greater than zero; see NOTES
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
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:
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.
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 details.
EMFILE The per-process limit on the number of open file descriptors has
ENFILE The system-wide limit on the total number of open files has been
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 informa-
tion as a hint for the amount of space to initially allocate in inter-
nal 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 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.
close(2), epoll_ctl(2), epoll_wait(2), epoll(7)
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