xref: /aosp_15_r20/external/libcups/scheduler/select.c (revision 5e7646d21f1134fb0638875d812ef646c12ab91e)

/*
 * Select abstraction functions for the CUPS scheduler.
 *
 * Copyright 2007-2016 by Apple Inc.
 * Copyright 2006-2007 by Easy Software Products.
 *
 * Licensed under Apache License v2.0.  See the file "LICENSE" for more information.
 */

/*
 * Include necessary headers...
 */

#include "cupsd.h"

#ifdef HAVE_EPOLL
#  include <sys/epoll.h>
#  include <poll.h>
#elif defined(HAVE_KQUEUE)
#  include <sys/event.h>
#  include <sys/time.h>
#elif defined(HAVE_POLL)
#  include <poll.h>
#else
#  include <sys/select.h>
#endif /* HAVE_EPOLL */


/*
 * Design Notes for Poll/Select API in CUPSD
 * -----------------------------------------
 *
 * SUPPORTED APIS
 *
 *     OS              select  poll    epoll   kqueue  /dev/poll
 *     --------------  ------  ------  ------  ------  ---------
 *     AIX             YES     YES     NO      NO      NO
 *     FreeBSD         YES     YES     NO      YES     NO
 *     HP-UX           YES     YES     NO      NO      NO
 *     Linux           YES     YES     YES     NO      NO
 *     macOS           YES     YES     NO      YES     NO
 *     NetBSD          YES     YES     NO      YES     NO
 *     OpenBSD         YES     YES     NO      YES     NO
 *     Solaris         YES     YES     NO      NO      YES
 *     Tru64           YES     YES     NO      NO      NO
 *     Windows         YES     NO      NO      NO      NO
 *
 *
 * HIGH-LEVEL API
 *
 *     typedef void (*cupsd_selfunc_t)(void *data);
 *
 *     void cupsdStartSelect(void);
 *     void cupsdStopSelect(void);
 *     void cupsdAddSelect(int fd, cupsd_selfunc_t read_cb,
 *                         cupsd_selfunc_t write_cb, void *data);
 *     void cupsdRemoveSelect(int fd);
 *     int cupsdDoSelect(int timeout);
 *
 *
 * IMPLEMENTATION STRATEGY
 *
 *     0. Common Stuff
 *         a. CUPS array of file descriptor to callback functions
 *            and data + temporary array of removed fd's.
 *         b. cupsdStartSelect() creates the arrays
 *         c. cupsdStopSelect() destroys the arrays and all elements.
 *         d. cupsdAddSelect() adds to the array and allocates a
 *            new callback element.
 *         e. cupsdRemoveSelect() removes from the active array and
 *            adds to the inactive array.
 *         f. _cupsd_fd_t provides a reference-counted structure for
 *            tracking file descriptors that are monitored.
 *         g. cupsdDoSelect() frees all inactive FDs.
 *
 *     1. select() O(n)
 *         a. Input/Output fd_set variables, copied to working
 *            copies and then used with select().
 *         b. Loop through CUPS array, using FD_ISSET and calling
 *            the read/write callbacks as needed.
 *         c. cupsdRemoveSelect() clears fd_set bit from main and
 *            working sets.
 *         d. cupsdStopSelect() frees all of the memory used by the
 *            CUPS array and fd_set's.
 *
 *     2. poll() - O(n log n)
 *         a. Regular array of pollfd, sorted the same as the CUPS
 *            array.
 *         b. Loop through pollfd array, call the corresponding
 *            read/write callbacks as needed.
 *         c. cupsdAddSelect() adds first to CUPS array and flags the
 *            pollfd array as invalid.
 *         d. cupsdDoSelect() rebuilds pollfd array as needed, calls
 *            poll(), then loops through the pollfd array looking up
 *            as needed.
 *         e. cupsdRemoveSelect() flags the pollfd array as invalid.
 *         f. cupsdStopSelect() frees all of the memory used by the
 *            CUPS array and pollfd array.
 *
 *     3. epoll() - O(n)
 *         a. cupsdStartSelect() creates epoll file descriptor using
 *            epoll_create() with the maximum fd count, and
 *            allocates an events buffer for the maximum fd count.
 *         b. cupsdAdd/RemoveSelect() uses epoll_ctl() to add
 *            (EPOLL_CTL_ADD) or remove (EPOLL_CTL_DEL) a single
 *            event using the level-triggered semantics. The event
 *            user data field is a pointer to the new callback array
 *            element.
 *         c. cupsdDoSelect() uses epoll_wait() with the global event
 *            buffer allocated in cupsdStartSelect() and then loops
 *            through the events, using the user data field to find
 *            the callback record.
 *         d. cupsdStopSelect() closes the epoll file descriptor and
 *            frees all of the memory used by the event buffer.
 *
 *     4. kqueue() - O(n)
 *         b. cupsdStartSelect() creates kqueue file descriptor
 *            using kqueue() function and allocates a global event
 *            buffer.
 *         c. cupsdAdd/RemoveSelect() uses EV_SET and kevent() to
 *            register the changes. The event user data field is a
 *            pointer to the new callback array element.
 *         d. cupsdDoSelect() uses kevent() to poll for events and
 *            loops through the events, using the user data field to
 *            find the callback record.
 *         e. cupsdStopSelect() closes the kqueue() file descriptor
 *            and frees all of the memory used by the event buffer.
 *
 *     5. /dev/poll - O(n log n) - NOT YET IMPLEMENTED
 *         a. cupsdStartSelect() opens /dev/poll and allocates an
 *            array of pollfd structs; on failure to open /dev/poll,
 *            revert to poll() system call.
 *         b. cupsdAddSelect() writes a single pollfd struct to
 *            /dev/poll with the new file descriptor and the
 *            POLLIN/POLLOUT flags.
 *         c. cupsdRemoveSelect() writes a single pollfd struct to
 *            /dev/poll with the file descriptor and the POLLREMOVE
 *            flag.
 *         d. cupsdDoSelect() uses the DP_POLL ioctl to retrieve
 *            events from /dev/poll and then loops through the
 *            returned pollfd array, looking up the file descriptors
 *            as needed.
 *         e. cupsdStopSelect() closes /dev/poll and frees the
 *            pollfd array.
 *
 * PERFORMANCE
 *
 *   In tests using the "make test" target with option 0 (keep cupsd
 *   running) and the "testspeed" program with "-c 50 -r 1000", epoll()
 *   performed 5.5% slower than select(), followed by kqueue() at 16%
 *   slower than select() and poll() at 18% slower than select().  Similar
 *   results were seen with twice the number of client connections.
 *
 *   The epoll() and kqueue() performance is likely limited by the
 *   number of system calls used to add/modify/remove file
 *   descriptors dynamically.  Further optimizations may be possible
 *   in the area of limiting use of cupsdAddSelect() and
 *   cupsdRemoveSelect(), however extreme care will be needed to avoid
 *   excess CPU usage and deadlock conditions.
 *
 *   We may be able to improve the poll() implementation simply by
 *   keeping the pollfd array sync'd with the _cupsd_fd_t array, as that
 *   will eliminate the rebuilding of the array whenever there is a
 *   change and eliminate the fd array lookups in the inner loop of
 *   cupsdDoSelect().
 *
 *   Since /dev/poll will never be able to use a shadow array, it may
 *   not make sense to implement support for it.  ioctl() overhead will
 *   impact performance as well, so my guess would be that, for CUPS,
 *   /dev/poll will yield a net performance loss.
 */

/*
 * Local structures...
 */

typedef struct _cupsd_fd_s
{
  int			fd,		/* File descriptor */
			use;		/* Use count */
  cupsd_selfunc_t	read_cb,	/* Read callback */
			write_cb;	/* Write callback */
  void			*data;		/* Data pointer for callbacks */
} _cupsd_fd_t;


/*
 * Local globals...
 */

static cups_array_t	*cupsd_fds = NULL;
#if defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
static cups_array_t	*cupsd_inactive_fds = NULL;
static int		cupsd_in_select = 0;
#endif /* HAVE_EPOLL || HAVE_KQUEUE */

#ifdef HAVE_KQUEUE
static int		cupsd_kqueue_fd = -1,
			cupsd_kqueue_changes = 0;
static struct kevent	*cupsd_kqueue_events = NULL;
#elif defined(HAVE_POLL)
static int		cupsd_alloc_pollfds = 0,
			cupsd_update_pollfds = 0;
static struct pollfd	*cupsd_pollfds = NULL;
#  ifdef HAVE_EPOLL
static int		cupsd_epoll_fd = -1;
static struct epoll_event *cupsd_epoll_events = NULL;
#  endif /* HAVE_EPOLL */
#else /* select() */
static fd_set		cupsd_global_input,
			cupsd_global_output,
			cupsd_current_input,
			cupsd_current_output;
#endif /* HAVE_KQUEUE */


/*
 * Local functions...
 */

static int		compare_fds(_cupsd_fd_t *a, _cupsd_fd_t *b);
static _cupsd_fd_t	*find_fd(int fd);
#define			release_fd(f) { \
			  (f)->use --; \
			  if (!(f)->use) free((f));\
			}
#define			retain_fd(f) (f)->use++


/*
 * 'cupsdAddSelect()' - Add a file descriptor to the list.
 */

int					/* O - 1 on success, 0 on error */
cupsdAddSelect(int             fd,	/* I - File descriptor */
               cupsd_selfunc_t read_cb,	/* I - Read callback */
               cupsd_selfunc_t write_cb,/* I - Write callback */
	       void            *data)	/* I - Data to pass to callback */
{
  _cupsd_fd_t	*fdptr;			/* File descriptor record */
#ifdef HAVE_EPOLL
  int		added;			/* 1 if added, 0 if modified */
#endif /* HAVE_EPOLL */


 /*
  * Range check input...
  */

  cupsdLogMessage(CUPSD_LOG_DEBUG2,
                  "cupsdAddSelect(fd=%d, read_cb=%p, write_cb=%p, data=%p)",
		  fd, read_cb, write_cb, data);

  if (fd < 0)
    return (0);

 /*
  * See if this FD has already been added...
  */

  if ((fdptr = find_fd(fd)) == NULL)
  {
   /*
    * No, add a new entry...
    */

    if ((fdptr = calloc(1, sizeof(_cupsd_fd_t))) == NULL)
      return (0);

    fdptr->fd  = fd;
    fdptr->use = 1;

    if (!cupsArrayAdd(cupsd_fds, fdptr))
    {
      cupsdLogMessage(CUPSD_LOG_EMERG, "Unable to add fd %d to array!", fd);
      free(fdptr);
      return (0);
    }

#ifdef HAVE_EPOLL
    added = 1;
  }
  else
    added = 0;
#else
  }
#endif /* HAVE_EPOLL */

#ifdef HAVE_KQUEUE
  {
    struct kevent	event;		/* Event data */
    struct timespec	timeout;	/* Timeout value */


    timeout.tv_sec  = 0;
    timeout.tv_nsec = 0;

    if (fdptr->read_cb != read_cb)
    {
      if (read_cb)
        EV_SET(&event, fd, EVFILT_READ, EV_ADD, 0, 0, fdptr);
      else
        EV_SET(&event, fd, EVFILT_READ, EV_DELETE, 0, 0, fdptr);

      if (kevent(cupsd_kqueue_fd, &event, 1, NULL, 0, &timeout))
      {
	cupsdLogMessage(CUPSD_LOG_EMERG, "kevent() returned %s",
			strerror(errno));
	return (0);
      }
    }

    if (fdptr->write_cb != write_cb)
    {
      if (write_cb)
        EV_SET(&event, fd, EVFILT_WRITE, EV_ADD, 0, 0, fdptr);
      else
        EV_SET(&event, fd, EVFILT_WRITE, EV_DELETE, 0, 0, fdptr);

      if (kevent(cupsd_kqueue_fd, &event, 1, NULL, 0, &timeout))
      {
	cupsdLogMessage(CUPSD_LOG_EMERG, "kevent() returned %s",
			strerror(errno));
	return (0);
      }
    }
  }

#elif defined(HAVE_POLL)
#  ifdef HAVE_EPOLL
  if (cupsd_epoll_fd >= 0)
  {
    struct epoll_event event;		/* Event data */


    event.events = 0;

    if (read_cb)
      event.events |= EPOLLIN;

    if (write_cb)
      event.events |= EPOLLOUT;

    event.data.ptr = fdptr;

    if (epoll_ctl(cupsd_epoll_fd, added ? EPOLL_CTL_ADD : EPOLL_CTL_MOD, fd,
                  &event))
    {
      close(cupsd_epoll_fd);
      cupsd_epoll_fd       = -1;
      cupsd_update_pollfds = 1;
    }
  }
  else
#  endif /* HAVE_EPOLL */

  cupsd_update_pollfds = 1;

#else /* select() */
 /*
  * Add or remove the file descriptor in the input and output sets
  * for select()...
  */

  if (read_cb)
    FD_SET(fd, &cupsd_global_input);
  else
  {
    FD_CLR(fd, &cupsd_global_input);
    FD_CLR(fd, &cupsd_current_input);
  }

  if (write_cb)
    FD_SET(fd, &cupsd_global_output);
  else
  {
    FD_CLR(fd, &cupsd_global_output);
    FD_CLR(fd, &cupsd_current_output);
  }
#endif /* HAVE_KQUEUE */

 /*
  * Save the (new) read and write callbacks...
  */

  fdptr->read_cb  = read_cb;
  fdptr->write_cb = write_cb;
  fdptr->data     = data;

  return (1);
}


/*
 * 'cupsdDoSelect()' - Do a select-like operation.
 */

int					/* O - Number of files or -1 on error */
cupsdDoSelect(long timeout)		/* I - Timeout in seconds */
{
  int			nfds;		/* Number of file descriptors */
  _cupsd_fd_t		*fdptr;		/* Current file descriptor */
#ifdef HAVE_KQUEUE
  int			i;		/* Looping var */
  struct kevent		*event;		/* Current event */
  struct timespec	ktimeout;	/* kevent() timeout */


  cupsd_in_select = 1;

  if (timeout >= 0 && timeout < 86400)
  {
    ktimeout.tv_sec  = timeout;
    ktimeout.tv_nsec = 0;

    nfds = kevent(cupsd_kqueue_fd, NULL, 0, cupsd_kqueue_events, MaxFDs,
                  &ktimeout);
  }
  else
    nfds = kevent(cupsd_kqueue_fd, NULL, 0, cupsd_kqueue_events, MaxFDs, NULL);

  cupsd_kqueue_changes = 0;

  for (i = nfds, event = cupsd_kqueue_events; i > 0; i --, event ++)
  {
    fdptr = (_cupsd_fd_t *)event->udata;

    if (cupsArrayFind(cupsd_inactive_fds, fdptr))
      continue;

    retain_fd(fdptr);

    if (fdptr->read_cb && event->filter == EVFILT_READ)
      (*(fdptr->read_cb))(fdptr->data);

    if (fdptr->use > 1 && fdptr->write_cb && event->filter == EVFILT_WRITE &&
        !cupsArrayFind(cupsd_inactive_fds, fdptr))
      (*(fdptr->write_cb))(fdptr->data);

    release_fd(fdptr);
  }

#elif defined(HAVE_POLL)
  struct pollfd		*pfd;		/* Current pollfd structure */
  int			count;		/* Number of file descriptors */


#  ifdef HAVE_EPOLL
  cupsd_in_select = 1;

  if (cupsd_epoll_fd >= 0)
  {
    int			i;		/* Looping var */
    struct epoll_event	*event;		/* Current event */


    if (timeout >= 0 && timeout < 86400)
      nfds = epoll_wait(cupsd_epoll_fd, cupsd_epoll_events, MaxFDs,
                	timeout * 1000);
    else
      nfds = epoll_wait(cupsd_epoll_fd, cupsd_epoll_events, MaxFDs, -1);

    if (nfds < 0 && errno != EINTR)
    {
      close(cupsd_epoll_fd);
      cupsd_epoll_fd = -1;
    }
    else
    {
      for (i = nfds, event = cupsd_epoll_events; i > 0; i --, event ++)
      {
	fdptr = (_cupsd_fd_t *)event->data.ptr;

	if (cupsArrayFind(cupsd_inactive_fds, fdptr))
	  continue;

	retain_fd(fdptr);

	if (fdptr->read_cb && (event->events & (EPOLLIN | EPOLLERR | EPOLLHUP)))
	  (*(fdptr->read_cb))(fdptr->data);

	if (fdptr->use > 1 && fdptr->write_cb &&
            (event->events & (EPOLLOUT | EPOLLERR | EPOLLHUP)) &&
            !cupsArrayFind(cupsd_inactive_fds, fdptr))
	  (*(fdptr->write_cb))(fdptr->data);

	release_fd(fdptr);
      }

      goto release_inactive;
    }
  }
#  endif /* HAVE_EPOLL */

  count = cupsArrayCount(cupsd_fds);

  if (cupsd_update_pollfds)
  {
   /*
    * Update the cupsd_pollfds array to match the current FD array...
    */

    cupsd_update_pollfds = 0;

   /*
    * (Re)allocate memory as needed...
    */

    if (count > cupsd_alloc_pollfds)
    {
      int allocfds = count + 16;


      if (cupsd_pollfds)
	pfd = realloc(cupsd_pollfds, (size_t)allocfds * sizeof(struct pollfd));
      else
	pfd = malloc((size_t)allocfds * sizeof(struct pollfd));

      if (!pfd)
      {
	cupsdLogMessage(CUPSD_LOG_EMERG, "Unable to allocate %d bytes for polling.", (int)((size_t)allocfds * sizeof(struct pollfd)));

	return (-1);
      }

      cupsd_pollfds       = pfd;
      cupsd_alloc_pollfds = allocfds;
    }

   /*
    * Rebuild the array...
    */

    for (fdptr = (_cupsd_fd_t *)cupsArrayFirst(cupsd_fds), pfd = cupsd_pollfds;
         fdptr;
	 fdptr = (_cupsd_fd_t *)cupsArrayNext(cupsd_fds), pfd ++)
    {
      pfd->fd      = fdptr->fd;
      pfd->events  = 0;

      if (fdptr->read_cb)
	pfd->events |= POLLIN;

      if (fdptr->write_cb)
	pfd->events |= POLLOUT;
    }
  }

  if (timeout >= 0 && timeout < 86400)
    nfds = poll(cupsd_pollfds, (nfds_t)count, timeout * 1000);
  else
    nfds = poll(cupsd_pollfds, (nfds_t)count, -1);

  if (nfds > 0)
  {
   /*
    * Do callbacks for each file descriptor...
    */

    for (pfd = cupsd_pollfds; count > 0; pfd ++, count --)
    {
      if (!pfd->revents)
        continue;

      if ((fdptr = find_fd(pfd->fd)) == NULL)
        continue;

      retain_fd(fdptr);

      if (fdptr->read_cb && (pfd->revents & (POLLIN | POLLERR | POLLHUP)))
        (*(fdptr->read_cb))(fdptr->data);

      if (fdptr->use > 1 && fdptr->write_cb &&
          (pfd->revents & (POLLOUT | POLLERR | POLLHUP)))
        (*(fdptr->write_cb))(fdptr->data);

      release_fd(fdptr);
    }
  }

#else /* select() */
  struct timeval	stimeout;	/* Timeout for select() */
  int			maxfd;		/* Maximum file descriptor */


 /*
  * Figure out the highest file descriptor number...
  */

  if ((fdptr = (_cupsd_fd_t *)cupsArrayLast(cupsd_fds)) == NULL)
    maxfd = 1;
  else
    maxfd = fdptr->fd + 1;

 /*
  * Do the select()...
  */

  cupsd_current_input  = cupsd_global_input;
  cupsd_current_output = cupsd_global_output;

  if (timeout >= 0 && timeout < 86400)
  {
    stimeout.tv_sec  = timeout;
    stimeout.tv_usec = 0;

    nfds = select(maxfd, &cupsd_current_input, &cupsd_current_output, NULL,
                  &stimeout);
  }
  else
    nfds = select(maxfd, &cupsd_current_input, &cupsd_current_output, NULL,
                  NULL);

  if (nfds > 0)
  {
   /*
    * Do callbacks for each file descriptor...
    */

    for (fdptr = (_cupsd_fd_t *)cupsArrayFirst(cupsd_fds);
         fdptr;
	 fdptr = (_cupsd_fd_t *)cupsArrayNext(cupsd_fds))
    {
      retain_fd(fdptr);

      if (fdptr->read_cb && FD_ISSET(fdptr->fd, &cupsd_current_input))
        (*(fdptr->read_cb))(fdptr->data);

      if (fdptr->use > 1 && fdptr->write_cb &&
          FD_ISSET(fdptr->fd, &cupsd_current_output))
        (*(fdptr->write_cb))(fdptr->data);

      release_fd(fdptr);
    }
  }

#endif /* HAVE_KQUEUE */

#if defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
 /*
  * Release all inactive file descriptors...
  */

#  ifndef HAVE_KQUEUE
  release_inactive:
#  endif /* !HAVE_KQUEUE */

  cupsd_in_select = 0;

  for (fdptr = (_cupsd_fd_t *)cupsArrayFirst(cupsd_inactive_fds);
       fdptr;
       fdptr = (_cupsd_fd_t *)cupsArrayNext(cupsd_inactive_fds))
  {
    cupsArrayRemove(cupsd_inactive_fds, fdptr);
    release_fd(fdptr);
  }
#endif /* HAVE_EPOLL || HAVE_KQUEUE */

 /*
  * Return the number of file descriptors handled...
  */

  return (nfds);
}


#ifdef CUPSD_IS_SELECTING
/*
 * 'cupsdIsSelecting()' - Determine whether we are monitoring a file
 *                        descriptor.
 */

int					/* O - 1 if selecting, 0 otherwise */
cupsdIsSelecting(int fd)		/* I - File descriptor */
{
  return (find_fd(fd) != NULL);
}
#endif /* CUPSD_IS_SELECTING */


/*
 * 'cupsdRemoveSelect()' - Remove a file descriptor from the list.
 */

void
cupsdRemoveSelect(int fd)		/* I - File descriptor */
{
  _cupsd_fd_t		*fdptr;		/* File descriptor record */
#ifdef HAVE_EPOLL
  struct epoll_event	event;		/* Event data */
#elif defined(HAVE_KQUEUE)
  struct kevent		event;		/* Event data */
  struct timespec	timeout;	/* Timeout value */
#elif defined(HAVE_POLL)
  /* No variables for poll() */
#endif /* HAVE_EPOLL */


 /*
  * Range check input...
  */

  cupsdLogMessage(CUPSD_LOG_DEBUG2, "cupsdRemoveSelect(fd=%d)", fd);

  if (fd < 0)
    return;

 /*
  * Find the file descriptor...
  */

  if ((fdptr = find_fd(fd)) == NULL)
    return;

#ifdef HAVE_EPOLL
  if (epoll_ctl(cupsd_epoll_fd, EPOLL_CTL_DEL, fd, &event))
  {
    close(cupsd_epoll_fd);
    cupsd_epoll_fd       = -1;
    cupsd_update_pollfds = 1;
  }

#elif defined(HAVE_KQUEUE)
  timeout.tv_sec  = 0;
  timeout.tv_nsec = 0;

  if (fdptr->read_cb)
  {
    EV_SET(&event, fd, EVFILT_READ, EV_DELETE, 0, 0, fdptr);

    if (kevent(cupsd_kqueue_fd, &event, 1, NULL, 0, &timeout))
    {
      cupsdLogMessage(CUPSD_LOG_EMERG, "kevent() returned %s",
		      strerror(errno));
      goto cleanup;
    }
  }

  if (fdptr->write_cb)
  {
    EV_SET(&event, fd, EVFILT_WRITE, EV_DELETE, 0, 0, fdptr);

    if (kevent(cupsd_kqueue_fd, &event, 1, NULL, 0, &timeout))
    {
      cupsdLogMessage(CUPSD_LOG_EMERG, "kevent() returned %s",
		      strerror(errno));
      goto cleanup;
    }
  }

#elif defined(HAVE_POLL)
 /*
  * Update the pollfds array...
  */

  cupsd_update_pollfds = 1;

#else /* select() */
  FD_CLR(fd, &cupsd_global_input);
  FD_CLR(fd, &cupsd_global_output);
  FD_CLR(fd, &cupsd_current_input);
  FD_CLR(fd, &cupsd_current_output);
#endif /* HAVE_EPOLL */

#ifdef HAVE_KQUEUE
  cleanup:
#endif /* HAVE_KQUEUE */

 /*
  * Remove the file descriptor from the active array and add to the
  * inactive array (or release, if we don't need the inactive array...)
  */

  cupsArrayRemove(cupsd_fds, fdptr);

#if defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
  if (cupsd_in_select)
    cupsArrayAdd(cupsd_inactive_fds, fdptr);
  else
#endif /* HAVE_EPOLL || HAVE_KQUEUE */

  release_fd(fdptr);
}


/*
 * 'cupsdStartSelect()' - Initialize the file polling engine.
 */

void
cupsdStartSelect(void)
{
  cupsdLogMessage(CUPSD_LOG_DEBUG, "cupsdStartSelect()");

  cupsd_fds = cupsArrayNew((cups_array_func_t)compare_fds, NULL);

#if defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
  cupsd_inactive_fds = cupsArrayNew((cups_array_func_t)compare_fds, NULL);
#endif /* HAVE_EPOLL || HAVE_KQUEUE */

#ifdef HAVE_EPOLL
  cupsd_epoll_fd       = epoll_create(MaxFDs);
  cupsd_epoll_events   = calloc((size_t)MaxFDs, sizeof(struct epoll_event));
  cupsd_update_pollfds = 0;

#elif defined(HAVE_KQUEUE)
  cupsd_kqueue_fd      = kqueue();
  cupsd_kqueue_changes = 0;
  cupsd_kqueue_events  = calloc((size_t)MaxFDs, sizeof(struct kevent));

#elif defined(HAVE_POLL)
  cupsd_update_pollfds = 0;

#else /* select() */
  FD_ZERO(&cupsd_global_input);
  FD_ZERO(&cupsd_global_output);
#endif /* HAVE_EPOLL */
}


/*
 * 'cupsdStopSelect()' - Shutdown the file polling engine.
 */

void
cupsdStopSelect(void)
{
  _cupsd_fd_t	*fdptr;			/* Current file descriptor */


  cupsdLogMessage(CUPSD_LOG_DEBUG, "cupsdStopSelect()");

  for (fdptr = (_cupsd_fd_t *)cupsArrayFirst(cupsd_fds);
       fdptr;
       fdptr = (_cupsd_fd_t *)cupsArrayNext(cupsd_fds))
    free(fdptr);

  cupsArrayDelete(cupsd_fds);
  cupsd_fds = NULL;

#if defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
  cupsArrayDelete(cupsd_inactive_fds);
  cupsd_inactive_fds = NULL;
#endif /* HAVE_EPOLL || HAVE_KQUEUE */

#ifdef HAVE_KQUEUE
  if (cupsd_kqueue_events)
  {
    free(cupsd_kqueue_events);
    cupsd_kqueue_events = NULL;
  }

  if (cupsd_kqueue_fd >= 0)
  {
    close(cupsd_kqueue_fd);
    cupsd_kqueue_fd = -1;
  }

  cupsd_kqueue_changes = 0;

#elif defined(HAVE_POLL)
#  ifdef HAVE_EPOLL
  if (cupsd_epoll_events)
  {
    free(cupsd_epoll_events);
    cupsd_epoll_events = NULL;
  }

  if (cupsd_epoll_fd >= 0)
  {
    close(cupsd_epoll_fd);
    cupsd_epoll_fd = -1;
  }
#  endif /* HAVE_EPOLL */

  if (cupsd_pollfds)
  {
    free(cupsd_pollfds);
    cupsd_pollfds       = NULL;
    cupsd_alloc_pollfds = 0;
  }

  cupsd_update_pollfds = 0;

#else /* select() */
  FD_ZERO(&cupsd_global_input);
  FD_ZERO(&cupsd_global_output);
#endif /* HAVE_EPOLL */
}


/*
 * 'compare_fds()' - Compare file descriptors.
 */

static int				/* O - Result of comparison */
compare_fds(_cupsd_fd_t *a,		/* I - First file descriptor */
            _cupsd_fd_t *b)		/* I - Second file descriptor */
{
  return (a->fd - b->fd);
}


/*
 * 'find_fd()' - Find an existing file descriptor record.
 */

static _cupsd_fd_t *			/* O - FD record pointer or NULL */
find_fd(int fd)				/* I - File descriptor */
{
  _cupsd_fd_t	*fdptr,			/* Matching record (if any) */
		key;			/* Search key */


  cupsArraySave(cupsd_fds);

  key.fd = fd;
  fdptr  = (_cupsd_fd_t *)cupsArrayFind(cupsd_fds, &key);

  cupsArrayRestore(cupsd_fds);

  return (fdptr);
}