epoll_create, epoll_create1 - open an epoll file descriptor
int epoll_create(int size);
int epoll_create1(int flags);
() creates an epoll(7)
instance. Since Linux 2.6.8,
argument is ignored, but must be greater than zero; see NOTES
() returns a file descriptor referring to the new epoll
instance. This file descriptor is used for all the subsequent calls to the
interface. When no longer required, the file descriptor returned
() 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.
is 0, then, other than the fact that the obsolete size
argument is dropped, epoll_create1
() is the same as
(). The following value can be included in flags
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.
- size is not positive.
- (epoll_create1()) Invalid value specified in flags.
- 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.
- The per-process limit on the number of open file descriptors has been
- The system-wide limit on the total number of open files has been
- There was insufficient memory to create the kernel object.
() was added to the kernel in version 2.6. Library support is
provided in glibc starting with version 2.3.2.
() was added to the kernel in version 2.6.27. Library
support is provided in glibc starting with version 2.9.
() is Linux-specific.
In the initial epoll_create
() implementation, the size
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
run on older kernels.
This page is part of release 4.10 of the Linux man-pages
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