/*

 * First Available Server load balancing algorithm.

 *

 * This file implements an algorithm which emerged during a discussion with

 * Steen Larsen, initially inspired from Anshul Gandhi et.al.'s work now

 * described as "packing" in section 3.5:

 *

 *    http://reports-archive.adm.cs.cmu.edu/anon/2012/CMU-CS-12-109.pdf

 *

 * Copyright 2000-2012 Willy Tarreau <w@1wt.eu>

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version

 * 2 of the License, or (at your option) any later version.

 *

 */

#include <import/eb32tree.h>

#include <haproxy/api.h>

#include <haproxy/backend.h>

#include <haproxy/proxy.h>

#include <haproxy/queue.h>

#include <haproxy/server-t.h>

/* Remove a server from a tree. It must have previously been dequeued. This

 * function is meant to be called when a server is going down or has its

 * weight disabled.

 *

 * The server's lock and the lbprm's lock must be held.

 */

static inline void fas_remove_from_tree(struct server *s)

{

  s->lb_tree = NULL;

}

/* simply removes a server from a tree.

 *

 * The lbprm's lock must be held.

 */

static inline void fas_dequeue_srv(struct server *s)

{

  eb32_delete(&s->lb_node);

}

/* Queue a server in its associated tree, assuming the weight is >0.

 * Servers are sorted by unique ID so that we send all connections to the first

 * available server in declaration order (or ID order) until its maxconn is

 * reached. It is important to understand that the server weight is not used

 * here.

 *

 * The lbprm's lock must be held.

 */

static inline void fas_queue_srv(struct server *s)

{

  s->lb_node.key = s->puid;

  eb32_insert(s->lb_tree, &s->lb_node);

}

/* Re-position the server in the FS tree after it has been assigned one

 * connection or after it has released one. Note that it is possible that

 * the server has been moved out of the tree due to failed health-checks.

 * The lbprm's lock will be used.

 */

static void fas_srv_reposition(struct server *s)

{

  HA_RWLOCK_WRLOCK(LBPRM_LOCK, &s->proxy->lbprm.lock);

  if (s->lb_tree) {

    fas_dequeue_srv(s);

    fas_queue_srv(s);

  }

  HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &s->proxy->lbprm.lock);

}

/* This function updates the server trees according to server <srv>'s new

 * state. It should be called when server <srv>'s status changes to down.

 * It is not important whether the server was already down or not. It is not

 * important either that the new state is completely down (the caller may not

 * know all the variables of a server's state).

 *

 * The server's lock must be held. The lbprm's lock will be used.

 */

static void fas_set_server_status_down(struct server *srv)

{

  struct proxy *p = srv->proxy;

  if (!srv_lb_status_changed(srv))

    return;

  if (srv_willbe_usable(srv))

    goto out_update_state;

  HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);

  if (!srv_currently_usable(srv))

    /* server was already down */

    goto out_update_backend;

  if (srv->flags & SRV_F_BACKUP) {

    p->lbprm.tot_wbck -= srv->cur_eweight;

    p->srv_bck--;

    if (srv == p->lbprm.fbck) {

      /* we lost the first backup server in a single-backup

       * configuration, we must search another one.

       */

      struct server *srv2 = p->lbprm.fbck;

      do {

        srv2 = proxy_next_server(srv2);

      } while (srv2 &&

         !((srv2->flags & SRV_F_BACKUP) &&

           srv_willbe_usable(srv2)));

      p->lbprm.fbck = srv2;

    }

  } else {

    p->lbprm.tot_wact -= srv->cur_eweight;

    p->srv_act--;

  }

  fas_dequeue_srv(srv);

  fas_remove_from_tree(srv);

 out_update_backend:

  /* check/update tot_used, tot_weight */

  update_backend_weight(p);

  HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);

 out_update_state:

  srv_lb_commit_status(srv);

}

/* This function updates the server trees according to server <srv>'s new

 * state. It should be called when server <srv>'s status changes to up.

 * It is not important whether the server was already down or not. It is not

 * important either that the new state is completely UP (the caller may not

 * know all the variables of a server's state). This function will not change

 * the weight of a server which was already up.

 *

 * The server's lock must be held. The lbprm's lock will be used.

 */

static void fas_set_server_status_up(struct server *srv)

{

  struct proxy *p = srv->proxy;

  if (!srv_lb_status_changed(srv))

    return;

  if (!srv_willbe_usable(srv))

    goto out_update_state;

  HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);

  if (srv_currently_usable(srv))

    /* server was already up */

    goto out_update_backend;

  if (srv->flags & SRV_F_BACKUP) {

    srv->lb_tree = &p->lbprm.fas.bck;

    p->lbprm.tot_wbck += srv->next_eweight;

    p->srv_bck++;

    if (!(p->options & PR_O_USE_ALL_BK)) {

      if (!p->lbprm.fbck) {

        /* there was no backup server anymore */

        p->lbprm.fbck = srv;

      } else {

        /* we may have restored a backup server prior to fbck,

         * in which case it should replace it.

         */

        struct server *srv2 = srv;

        do {

          srv2 = proxy_next_server(srv2);

        } while (srv2 && (srv2 != p->lbprm.fbck));

        if (srv2)

          p->lbprm.fbck = srv;

      }

    }

  } else {

    srv->lb_tree = &p->lbprm.fas.act;

    p->lbprm.tot_wact += srv->next_eweight;

    p->srv_act++;

  }

  /* note that eweight cannot be 0 here */

  fas_queue_srv(srv);

 out_update_backend:

  /* check/update tot_used, tot_weight */

  update_backend_weight(p);

  HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);

 out_update_state:

  srv_lb_commit_status(srv);

}

/* This function must be called after an update to server <srv>'s effective

 * weight. It may be called after a state change too.

 *

 * The server's lock must be held. The lbprm's lock will be used.

 */

static void fas_update_server_weight(struct server *srv)

{

  int old_state, new_state;

  struct proxy *p = srv->proxy;

  if (!srv_lb_status_changed(srv))

    return;

  /* If changing the server's weight changes its state, we simply apply

   * the procedures we already have for status change. If the state

   * remains down, the server is not in any tree, so it's as easy as

   * updating its values. If the state remains up with different weights,

   * there are some computations to perform to find a new place and

   * possibly a new tree for this server.

   */

  old_state = srv_currently_usable(srv);

  new_state = srv_willbe_usable(srv);

  if (!old_state && !new_state) {

    srv_lb_commit_status(srv);

    return;

  }

  else if (!old_state && new_state) {

    fas_set_server_status_up(srv);

    return;

  }

  else if (old_state && !new_state) {

    fas_set_server_status_down(srv);

    return;

  }

  HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);

  if (srv->lb_tree)

    fas_dequeue_srv(srv);

  if (srv->flags & SRV_F_BACKUP) {

    p->lbprm.tot_wbck += srv->next_eweight - srv->cur_eweight;

    srv->lb_tree = &p->lbprm.fas.bck;

  } else {

    p->lbprm.tot_wact += srv->next_eweight - srv->cur_eweight;

    srv->lb_tree = &p->lbprm.fas.act;

  }

  fas_queue_srv(srv);

  update_backend_weight(p);

  HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);

  srv_lb_commit_status(srv);

}

/* This function is responsible for building the trees in case of fast

 * weighted least-conns. It also sets p->lbprm.wdiv to the eweight to

 * uweight ratio. Both active and backup groups are initialized.

 */

static int fas_init_server_tree(struct proxy *p)

{

  struct server *srv;

  struct eb_root init_head = EB_ROOT;

  p->lbprm.wdiv = BE_WEIGHT_SCALE;

  list_for_each_entry(srv, &p->servers, el_px) {

    srv->next_eweight = (srv->uweight * p->lbprm.wdiv + p->lbprm.wmult - 1) / p->lbprm.wmult;

    srv_lb_commit_status(srv);

  }

  recount_servers(p);

  update_backend_weight(p);

  p->lbprm.fas.act = init_head;

  p->lbprm.fas.bck = init_head;

  /* queue active and backup servers in two distinct groups */

  list_for_each_entry(srv, &p->servers, el_px) {

    if (!srv_currently_usable(srv))

      continue;

    srv->lb_tree = (srv->flags & SRV_F_BACKUP) ? &p->lbprm.fas.bck : &p->lbprm.fas.act;

    fas_queue_srv(srv);

  }

  return 0;

}

/* Return next server from the FS tree in backend <p>. If the tree is empty,

 * return NULL. Saturated servers are skipped.

 *

 * The lbprm's lock will be used. The server's lock is not used.

 */

struct server *fas_get_next_server(struct proxy *p, struct server *srvtoavoid)

{

  struct server *srv, *avoided;

  struct eb32_node *node;

  srv = avoided = NULL;

  HA_RWLOCK_RDLOCK(LBPRM_LOCK, &p->lbprm.lock);

  if (p->srv_act)

    node = eb32_first(&p->lbprm.fas.act);

  else if (p->lbprm.fbck) {

    srv = p->lbprm.fbck;

    goto out;

  }

  else if (p->srv_bck)

    node = eb32_first(&p->lbprm.fas.bck);

  else {

    srv = NULL;

    goto out;

  }

  while (node) {

    /* OK, we have a server. However, it may be saturated, in which

     * case we don't want to reconsider it for now, so we'll simply

     * skip it. Same if it's the server we try to avoid, in which

     * case we simply remember it for later use if needed.

     */

    struct server *s;

    s = eb32_entry(node, struct server, lb_node);

    if (!s->maxconn || (!s->queueslength && s->served < srv_dynamic_maxconn(s))) {

      if (s != srvtoavoid) {

        srv = s;

        break;

      }

      avoided = s;

    }

    node = eb32_next(node);

  }

  if (!srv)

    srv = avoided;

  out:

  HA_RWLOCK_RDUNLOCK(LBPRM_LOCK, &p->lbprm.lock);

  return srv;

}

static struct lb_ops lb_fas_ops = {ILH,

  .map = {

    { .mask = BE_LB_KIND | BE_LB_PARM, .match = BE_LB_KIND_CB | BE_LB_CB_FAS },

    { 0, 0 }

  },

  .algo_prop              = BE_LB_LKUP_FSTREE | BE_LB_PROP_DYN,

  .proxy_init             = fas_init_server_tree,

  .set_server_status_up   = fas_set_server_status_up,

  .set_server_status_down = fas_set_server_status_down,

  .update_server_eweight  = fas_update_server_weight,

  .server_take_conn       = fas_srv_reposition,

  .server_drop_conn       = fas_srv_reposition,

};

INITCALL1(STG_REGISTER, lb_ops_register, &lb_fas_ops);

/*

 * Local variables:

 *  c-indent-level: 8

 *  c-basic-offset: 8

 * End:

 */