Add in independent byrequests lbmethod

/* Licensed to the Apache Software Foundation (ASF) under one or more

 * contributor license agreements.  See the NOTICE file distributed with

 * this work for additional information regarding copyright ownership.

 * The ASF licenses this file to You under the Apache License, Version 2.0

 * (the "License"); you may not use this file except in compliance with

 * the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#include "mod_proxy.h"

#include "scoreboard.h"

#include "ap_mpm.h"

#include "apr_version.h"

#include "apr_hooks.h"

module AP_MODULE_DECLARE_DATA lbmethod_byrequests_module;

/*

 * The idea behind the find_best_byrequests scheduler is the following:

 *

 * lbfactor is "how much we expect this worker to work", or "the worker's

 * normalized work quota".

 *

 * lbstatus is "how urgent this worker has to work to fulfill its quota

 * of work".

 *

 * We distribute each worker's work quota to the worker, and then look

 * which of them needs to work most urgently (biggest lbstatus).  This

 * worker is then selected for work, and its lbstatus reduced by the

 * total work quota we distributed to all workers.  Thus the sum of all

 * lbstatus does not change.(*)

 *

 * If some workers are disabled, the others will

 * still be scheduled correctly.

 *

 * If a balancer is configured as follows:

 *

 * worker     a    b    c    d

 * lbfactor  25   25   25   25

 *

 * And b gets disabled, the following schedule is produced:

 *

 *    a c d a c d a c d ...

 *

 * Note that the above lbfactor setting is the *exact* same as:

 *

 * worker     a    b    c    d

 * lbfactor   1    1    1    1

 *

 * Asymmetric configurations work as one would expect. For

 * example:

 *

 * worker     a    b    c    d

 * lbfactor   1    1    1    2

 *

 * would have a, b and c all handling about the same

 * amount of load with d handling twice what a or b

 * or c handles individually. So we could see:

 *

 *   b a d c d a c d b d ...

 *

 */

static proxy_worker *find_best_byrequests(proxy_balancer *balancer,

                                request_rec *r)

{

    int i;

    int total_factor = 0;

    proxy_worker *worker;

    proxy_worker *mycandidate = NULL;

    int cur_lbset = 0;

    int max_lbset = 0;

    int checking_standby;

    int checked_standby;

    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,

                 "proxy: Entering byrequests for BALANCER (%s)",

                 balancer->name);

    /* First try to see if we have available candidate */

    do {

        checking_standby = checked_standby = 0;

        while (!mycandidate && !checked_standby) {

            worker = (proxy_worker *)balancer->workers->elts;

            for (i = 0; i < balancer->workers->nelts; i++, worker++) {

                if (!checking_standby) {    /* first time through */

                    if (worker->s->lbset > max_lbset)

                        max_lbset = worker->s->lbset;

                }

                if (worker->s->lbset > cur_lbset)

                    continue;

                if ( (checking_standby ? !PROXY_WORKER_IS_STANDBY(worker) : PROXY_WORKER_IS_STANDBY(worker)) )

                    continue;

                /* If the worker is in error state run

                 * retry on that worker. It will be marked as

                 * operational if the retry timeout is elapsed.

                 * The worker might still be unusable, but we try

                 * anyway.

                 */

                if (!PROXY_WORKER_IS_USABLE(worker))

                    ap_proxy_retry_worker("BALANCER", worker, r->server);

                /* Take into calculation only the workers that are

                 * not in error state or not disabled.

                 */

                if (PROXY_WORKER_IS_USABLE(worker)) {

                    worker->s->lbstatus += worker->s->lbfactor;

                    total_factor += worker->s->lbfactor;

                    if (!mycandidate || worker->s->lbstatus > mycandidate->s->lbstatus)

                        mycandidate = worker;

                }

            }

            checked_standby = checking_standby++;

        }

        cur_lbset++;

    } while (cur_lbset <= max_lbset && !mycandidate);

    if (mycandidate) {

        mycandidate->s->lbstatus -= total_factor;

        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,

                     "proxy: byrequests selected worker \"%s\" : busy %" APR_SIZE_T_FMT " : lbstatus %d",

                     mycandidate->name, mycandidate->s->busy, mycandidate->s->lbstatus);

    }

    return mycandidate;

}

/*

 * How to add additional lbmethods:

 *   1. Create func which determines "best" candidate worker

 *      (eg: find_best_bytraffic, above)

 *   2. Register it as a provider.

 */

static const proxy_balancer_method byrequests =

{

    "byrequests",

    &find_best_byrequests,

    NULL

};

static void register_hook(apr_pool_t *p)

{

    /* Only the mpm_winnt has child init hook handler.

     * make sure that we are called after the mpm

     * initializes and after the mod_proxy

     */

    ap_register_provider(p, PROXY_LBMETHOD, "byrequests", "0", &byrequests);

}

module AP_MODULE_DECLARE_DATA lbmethod_byrequests_module = {

    STANDARD20_MODULE_STUFF,

    NULL,       /* create per-directory config structure */

    NULL,       /* merge per-directory config structures */

    NULL,       /* create per-server config structure */

    NULL,       /* merge per-server config structures */

    NULL,       /* command apr_table_t */

    register_hook /* register hooks */

};