NAME

       epoll_create, epoll_create1 - open an epoll file descriptor

LIBRARY

       Standard C library (libc, -lc)

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 HISTORY.

       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 file descriptor (a nonnegative integer).  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-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.

STANDARDS

       Linux.

HISTORY

       epoll_create()
              Linux 2.6, glibc 2.3.2.

       epoll_create1()
              Linux 2.6.27, glibc 2.9.

       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.

       Prior  to  Linux  2.6.29, a /proc/sys/fs/epoll/max_user_instances kernel parameter limited
       live epolls for each real user ID, and  caused  epoll_create()  to  fail  with  EMFILE  on
       overrun.

SEE ALSO

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