text: /*
   * libev epoll fd activity backend
   *
   * Copyright (c) 2007,2008,2009,2010,2011 Marc Alexander Lehmann <libev@schmorp.de>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without modifica-
   * tion, are permitted provided that the following conditions are met:
   *
   *   1.  Redistributions of source code must retain the above copyright notice,
   *       this list of conditions and the following disclaimer.
   *
   *   2.  Redistributions in binary form must reproduce the above copyright
   *       notice, this list of conditions and the following disclaimer in the
   *       documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
   * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO
   * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
   * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
   * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
   * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * Alternatively, the contents of this file may be used under the terms of
   * the GNU General Public License ("GPL") version 2 or any later version,
   * in which case the provisions of the GPL are applicable instead of
   * the above. If you wish to allow the use of your version of this file
   * only under the terms of the GPL and not to allow others to use your
   * version of this file under the BSD license, indicate your decision
   * by deleting the provisions above and replace them with the notice
   * and other provisions required by the GPL. If you do not delete the
   * provisions above, a recipient may use your version of this file under
   * either the BSD or the GPL.
   */
  
  /*
   * general notes about epoll:
   *
   * a) epoll silently removes fds from the fd set. as nothing tells us
   *    that an fd has been removed otherwise, we have to continually
   *    "rearm" fds that we suspect *might* have changed (same
   *    problem with kqueue, but much less costly there).
   * b) the fact that ADD != MOD creates a lot of extra syscalls due to a)
   *    and seems not to have any advantage.
   * c) the inability to handle fork or file descriptors (think dup)
   *    limits the applicability over poll, so this is not a generic
   *    poll replacement.
   * d) epoll doesn't work the same as select with many file descriptors
   *    (such as files). while not critical, no other advanced interface
   *    seems to share this (rather non-unixy) limitation.
   * e) epoll claims to be embeddable, but in practise you never get
   *    a ready event for the epoll fd (broken: <=2.6.26, working: >=2.6.32).
   * f) epoll_ctl returning EPERM means the fd is always ready.
   *
   * lots of "weird code" and complication handling in this file is due
   * to these design problems with epoll, as we try very hard to avoid
   * epoll_ctl syscalls for common usage patterns and handle the breakage
   * ensuing from receiving events for closed and otherwise long gone
   * file descriptors.
   */
  
  #include <sys/epoll.h>
  
  #define EV_EMASK_EPERM 0x80
  
  static void
  epoll_modify (EV_P_ int fd, int oev, int nev)
  {
    struct epoll_event ev;
    unsigned char oldmask;
  
    /*
     * we handle EPOLL_CTL_DEL by ignoring it here
     * on the assumption that the fd is gone anyways
     * if that is wrong, we have to handle the spurious
     * event in epoll_poll.
     * if the fd is added again, we try to ADD it, and, if that
     * fails, we assume it still has the same eventmask.
     */
    if (!nev)
      return;
  
    oldmask = anfds [fd].emask;
    anfds [fd].emask = nev;
  
    /* store the generation counter in the upper 32 bits, the fd in the lower 32 bits */
    ev.data.u64 = (uint64_t)(uint32_t)fd
                | ((uint64_t)(uint32_t)++anfds [fd].egen << 32);
    ev.events   = (nev & EV_READ  ? EPOLLIN  : 0)
                | (nev & EV_WRITE ? EPOLLOUT : 0);
  
    if (expect_true (!epoll_ctl (backend_fd, oev && oldmask != nev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev)))
      return;
  
    if (expect_true (errno == ENOENT))
      {
        /* if ENOENT then the fd went away, so try to do the right thing */
        if (!nev)
          goto dec_egen;
  
        if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))
          return;
      }
    else if (expect_true (errno == EEXIST))
      {
        /* EEXIST means we ignored a previous DEL, but the fd is still active */
        /* if the kernel mask is the same as the new mask, we assume it hasn't changed */
        if (oldmask == nev)
          goto dec_egen;
  
        if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev))
          return;
      }
    else if (expect_true (errno == EPERM))
      {
        /* EPERM means the fd is always ready, but epoll is too snobbish */
        /* to handle it, unlike select or poll. */
        anfds [fd].emask = EV_EMASK_EPERM;
  
        /* add fd to epoll_eperms, if not already inside */
        if (!(oldmask & EV_EMASK_EPERM))
          {
            array_needsize (int, epoll_eperms, epoll_epermmax, epoll_epermcnt + 1, EMPTY2);
            epoll_eperms [epoll_epermcnt++] = fd;
          }
  
        return;
      }
  
    fd_kill (EV_A_ fd);
  
  dec_egen:
    /* we didn't successfully call epoll_ctl, so decrement the generation counter again */
    --anfds [fd].egen;
  }
  
  static void
  epoll_poll (EV_P_ ev_tstamp timeout)
  {
    int i;
    int eventcnt;
  
    if (expect_false (epoll_epermcnt))
      timeout = 0.;
  
    /* epoll wait times cannot be larger than (LONG_MAX - 999UL) / HZ msecs, which is below */
    /* the default libev max wait time, however. */
    EV_RELEASE_CB;
    eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, timeout * 1e3);
    EV_ACQUIRE_CB;
  
    if (expect_false (eventcnt < 0))
      {
        if (errno != EINTR)
          ev_syserr ("(libev) epoll_wait");
  
        return;
      }
  
    for (i = 0; i < eventcnt; ++i)
      {
        struct epoll_event *ev = epoll_events + i;
  
        int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */
        int want = anfds [fd].events;
        int got  = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
                 | (ev->events & (EPOLLIN  | EPOLLERR | EPOLLHUP) ? EV_READ  : 0);
  
        /*
         * check for spurious notification.
         * this only finds spurious notifications on egen updates
         * other spurious notifications will be found by epoll_ctl, below
         * we assume that fd is always in range, as we never shrink the anfds array
         */
        if (expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32)))
          {
            /* recreate kernel state */
            postfork |= 2;
            continue;
          }
  
        if (expect_false (got & ~want))
          {
            anfds [fd].emask = want;
  
            /*
             * we received an event but are not interested in it, try mod or del
             * this often happens because we optimistically do not unregister fds
             * when we are no longer interested in them, but also when we get spurious
             * notifications for fds from another process. this is partially handled
             * above with the gencounter check (== our fd is not the event fd), and
             * partially here, when epoll_ctl returns an error (== a child has the fd
             * but we closed it).
             */
            ev->events = (want & EV_READ  ? EPOLLIN  : 0)
                       | (want & EV_WRITE ? EPOLLOUT : 0);
  
            /* pre-2.6.9 kernels require a non-null pointer with EPOLL_CTL_DEL, */
            /* which is fortunately easy to do for us. */
            if (epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev))
              {
                postfork |= 2; /* an error occurred, recreate kernel state */
                continue;
              }
          }
  
        fd_event (EV_A_ fd, got);
      }
  
    /* if the receive array was full, increase its size */
    if (expect_false (eventcnt == epoll_eventmax))
      {
        ev_free (epoll_events);
        epoll_eventmax = array_nextsize (sizeof (struct epoll_event), epoll_eventmax, epoll_eventmax + 1);
        epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);
      }
  
    /* now synthesize events for all fds where epoll fails, while select works... */
    for (i = epoll_epermcnt; i--; )
      {
        int fd = epoll_eperms [i];
        unsigned char events = anfds [fd].events & (EV_READ | EV_WRITE);
  
        if (anfds [fd].emask & EV_EMASK_EPERM && events)
          fd_event (EV_A_ fd, events);
        else
          {
            epoll_eperms [i] = epoll_eperms [--epoll_epermcnt];
            anfds [fd].emask = 0;
          }
      }
  }
  
  inline_size
  int
  epoll_init (EV_P_ int flags)
  {
  #ifdef EPOLL_CLOEXEC
  #if !defined __ANDROID__ || __ANDROID_API__ >= 21
    backend_fd = epoll_create1 (EPOLL_CLOEXEC);
  
    if (backend_fd < 0 && (errno == EINVAL || errno == ENOSYS))
  #endif
  #endif
      backend_fd = epoll_create (256);
  
    if (backend_fd < 0)
      return 0;
  
    fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
  
    backend_mintime = 1e-3; /* epoll does sometimes return early, this is just to avoid the worst */
    backend_modify  = epoll_modify;
    backend_poll    = epoll_poll;
  
    epoll_eventmax = 64; /* initial number of events receivable per poll */
    epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);
  
    return EVBACKEND_EPOLL;
  }
  
  inline_size
  void
  epoll_destroy (EV_P)
  {
    ev_free (epoll_events);
    array_free (epoll_eperm, EMPTY);
  }
  
  inline_size
  void
  epoll_fork (EV_P)
  {
    close (backend_fd);
  
    while ((backend_fd = epoll_create (256)) < 0)
      ev_syserr ("(libev) epoll_create");
  
    fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
  
    fd_rearm_all (EV_A);
  }
  
  