/*
  *  OpenVPN -- An application to securely tunnel IP networks
  *             over a single TCP/UDP port, with support for SSL/TLS-based
  *             session authentication and key exchange,
  *             packet encryption, packet authentication, and
  *             packet compression.
  *

  *  Copyright (C) 2002-2018 OpenVPN Inc <sales@openvpn.net>

  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License version 2
  *  as published by the Free Software Foundation.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *

  *  You should have received a copy of the GNU General Public License along
  *  with this program; if not, write to the Free Software Foundation, Inc.,
  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

  */
 
 #ifndef SCHEDULE_H
 #define SCHEDULE_H
 
 /*
  * This code implements an efficient scheduler using
  * a random treap binary tree.
  *
  * The scheduler is used by the server executive to
  * keep track of which instances need service at a
  * known time in the future.  Instances need to
  * schedule events for things such as sending
  * a ping or scheduling a TLS renegotiation.
  */
 
 #if P2MP_SERVER
 
 /* define to enable a special test mode */
 /*#define SCHEDULE_TEST*/
 
 #include "otime.h"
 #include "error.h"
 
 struct schedule_entry
 {

     struct timeval tv;           /* wakeup time */
     unsigned int pri;            /* random treap priority */
     struct schedule_entry *parent; /* treap (btree) links */
     struct schedule_entry *lt;
     struct schedule_entry *gt;

 };
 
 struct schedule
 {

     struct schedule_entry *earliest_wakeup; /* cached earliest wakeup */
     struct schedule_entry *root;          /* the root of the treap (btree) */

 };
 
 /* Public functions */
 

 struct schedule *schedule_init(void);
 
 void schedule_free(struct schedule *s);
 
 void schedule_remove_entry(struct schedule *s, struct schedule_entry *e);

 
 #ifdef SCHEDULE_TEST

 void schedule_test(void);
 

 #endif
 
 /* Private Functions */
 
 /* is node already in tree? */
 #define IN_TREE(e) ((e)->pri)
 

 struct schedule_entry *schedule_find_least(struct schedule_entry *e);
 
 void schedule_add_modify(struct schedule *s, struct schedule_entry *e);
 
 void schedule_remove_node(struct schedule *s, struct schedule_entry *e);

 
 /* Public inline functions */
 
 /*
  * Add a struct schedule_entry (whose storage is managed by
  * caller) to the btree.  tv signifies the wakeup time for
  * a future event.  sigma is a time interval measured
  * in microseconds -- the event window being represented
  * starts at (tv - sigma) and ends at (tv + sigma).
  * Event signaling can occur anywere within this interval.
  * Making the interval larger makes the scheduler more efficient,
  * while making it smaller results in more precise scheduling.
  * The caller should treat the passed struct schedule_entry as
  * an opaque object.
  */
 static inline void

 schedule_add_entry(struct schedule *s,
                    struct schedule_entry *e,
                    const struct timeval *tv,
                    unsigned int sigma)

 {

     if (!IN_TREE(e) || !sigma || !tv_within_sigma(tv, &e->tv, sigma))

     {

         e->tv = *tv;
         schedule_add_modify(s, e);
         s->earliest_wakeup = NULL; /* invalidate cache */

     }
 }
 
 /*
  * Return the node with the earliest wakeup time.  If two
  * nodes have the exact same wakeup time, select based on
  * the random priority assigned to each node (the priority
  * is randomized every time an entry is re-added).
  */
 static inline struct schedule_entry *

 schedule_get_earliest_wakeup(struct schedule *s,
                              struct timeval *wakeup)

 {

     struct schedule_entry *ret;

     /* cache result */
     if (!s->earliest_wakeup)
     {
         s->earliest_wakeup = schedule_find_least(s->root);
     }
     ret = s->earliest_wakeup;
     if (ret)
     {
         *wakeup = ret->tv;
     }

     return ret;

 }
 

 #endif /* if P2MP_SERVER */
 #endif /* ifndef SCHEDULE_H */