epoll_create

EPOLL_CREATE(2)            Linux Programmer's Manual           EPOLL_CREATE(2)



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 a new 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.

   epoll_create1()
       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:

       EPOLL_CLOEXEC
              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.

RETURN VALUE
       On success, these system calls return a nonnegative file descriptor.
       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-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
              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 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 compatibility when new epoll applications are run on older
       kernels.

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

COLOPHON
       This page is part of release 5.03 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux                             2017-09-15                   EPOLL_CREATE(2)