/*
 * Copyright (c) 1997-2014 Erez Zadok
 * Copyright (c) 1989 Jan-Simon Pendry
 * Copyright (c) 1989 Imperial College of Science, Technology & Medicine
 * Copyright (c) 1989 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry at Imperial College, London.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 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 OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *
 * File: am-utils/amd/clock.c
 *
 */

/*
 * Callouts.
 *
 * Modeled on kernel object of the same name.
 * See usual references.
 *
 * Use of a heap-based mechanism was rejected:
 * 1.  more complex implementation needed.
 * 2.  not obvious that a list is too slow for Amd.
 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif /* HAVE_CONFIG_H */
#include <am_defs.h>
#include <amd.h>

void reschedule_timeouts(time_t now, time_t then);

typedef struct callout callout;
struct callout {
  callout *c_next;		/* List of callouts */
  callout_fun *c_fn;		/* Function to call */
  opaque_t c_arg;		/* Argument to pass to call */
  time_t c_time;		/* Time of call */
  int c_id;			/* Unique identifier */
};

static callout callouts;	/* List of pending callouts */
static callout *free_callouts;	/* Cache of free callouts */
static int nfree_callouts;	/* Number on free list */
static int callout_id;		/* Next free callout identifier */

time_t next_softclock;		/* Time of next call to softclock() */


/*
 * Number of callout slots we keep on the free list
 */
#define	CALLOUT_FREE_SLOP	10

/*
 * Global assumption: valid id's are non-zero.
 */
#define	CID_ALLOC()		(++callout_id)
#define	CID_UNDEF		(0)


static callout *
alloc_callout(void)
{
  callout *cp = free_callouts;

  if (cp) {
    --nfree_callouts;
    free_callouts = free_callouts->c_next;
    return cp;
  }
  return ALLOC(struct callout);
}


static void
free_callout(callout *cp)
{
  if (nfree_callouts > CALLOUT_FREE_SLOP) {
    XFREE(cp);
  } else {
    cp->c_next = free_callouts;
    free_callouts = cp;
    nfree_callouts++;
  }
}


/*
 * Schedule a callout.
 *
 * (*fn)(fn_arg) will be called at clocktime(NULL) + secs
 */
int
timeout(u_int secs, callout_fun *fn, opaque_t fn_arg)
{
  callout *cp, *cp2;
  time_t t = clocktime(NULL) + secs;

  /*
   * Allocate and fill in a new callout structure
   */
  callout *cpnew = alloc_callout();
  cpnew->c_arg = fn_arg;
  cpnew->c_fn = fn;
  cpnew->c_time = t;
  cpnew->c_id = CID_ALLOC();

  if (t < next_softclock)
    next_softclock = t;

  /*
   * Find the correct place in the list
   */
  for (cp = &callouts; (cp2 = cp->c_next); cp = cp2)
    if (cp2->c_time >= t)
      break;

  /*
   * And link it in
   */
  cp->c_next = cpnew;
  cpnew->c_next = cp2;

  /*
   * Return callout identifier
   */
  return cpnew->c_id;
}


/*
 * De-schedule a callout
 */
void
untimeout(int id)
{
  callout *cp, *cp2;
  for (cp = &callouts; (cp2 = cp->c_next); cp = cp2) {
    if (cp2->c_id == id) {
      cp->c_next = cp2->c_next;
      free_callout(cp2);
      break;
    }
  }
}


/*
 * Reschedule after clock changed
 */
void
reschedule_timeouts(time_t now, time_t then)
{
  callout *cp;

  for (cp = callouts.c_next; cp; cp = cp->c_next) {
    if (cp->c_time >= now && cp->c_time <= then) {
      plog(XLOG_WARNING, "job %d rescheduled to run immediately", cp->c_id);
      dlog("rescheduling job %d back %ld seconds",
	   cp->c_id, (long) (cp->c_time - now));
      next_softclock = cp->c_time = now;
    }
  }
}


/*
 * Clock handler
 */
int
softclock(void)
{
  time_t now;
  callout *cp;

  do {
    if (task_notify_todo)
      do_task_notify();

    now = clocktime(NULL);

    /*
     * While there are more callouts waiting...
     */
    while ((cp = callouts.c_next) && cp->c_time <= now) {
      /*
       * Extract first from list, save fn & fn_arg and
       * unlink callout from list and free.
       * Finally call function.
       *
       * The free is done first because
       * it is quite common that the
       * function will call timeout()
       * and try to allocate a callout
       */
      callout_fun *fn = cp->c_fn;
      opaque_t fn_arg = cp->c_arg;

      callouts.c_next = cp->c_next;
      free_callout(cp);
      (*fn) (fn_arg);
    }

  } while (task_notify_todo);

  /*
   * Return number of seconds to next event,
   * or 0 if there is no event.
   */
  if ((cp = callouts.c_next))
    return cp->c_time - now;
  return 0;
}