/* 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 "ap_hooks.h"

module AP_MODULE_DECLARE_DATA lbmethod_byrequests_module;

static APR_OPTIONAL_FN_TYPE(proxy_balancer_get_best_worker)

                            *ap_proxy_balancer_get_best_worker_fn = NULL;

static int is_best_byrequests(proxy_worker *current, proxy_worker *prev_best, void *baton)

{

    int *total_factor = (int *)baton;

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

    *total_factor += current->s->lbfactor;

    return (!prev_best || (current->s->lbstatus > prev_best->s->lbstatus));

}

/*

 * 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 total_factor = 0;

    proxy_worker *worker = ap_proxy_balancer_get_best_worker_fn(balancer, r, is_best_byrequests, &total_factor);

    if (worker) {

        worker->s->lbstatus -= total_factor;

    }

    return worker;

}

/* assumed to be mutex protected by caller */

static apr_status_t reset(proxy_balancer *balancer, server_rec *s)

{

    int i;

    proxy_worker **worker;

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

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

        (*worker)->s->lbstatus = 0;

    }

    return APR_SUCCESS;

}

static apr_status_t age(proxy_balancer *balancer, server_rec *s)

{

    return APR_SUCCESS;

}

/*

 * 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,

    &reset,

    &age,

    NULL

};

/* post_config hook: */

static int lbmethod_byrequests_post_config(apr_pool_t *pconf, apr_pool_t *plog,

        apr_pool_t *ptemp, server_rec *s)

{

    /* lbmethod_byrequests_post_config() will be called twice during startup.  So, don't

     * set up the static data the 1st time through. */

    if (ap_state_query(AP_SQ_MAIN_STATE) == AP_SQ_MS_CREATE_PRE_CONFIG) {

        return OK;

    }

    ap_proxy_balancer_get_best_worker_fn =

                 APR_RETRIEVE_OPTIONAL_FN(proxy_balancer_get_best_worker);

    if (!ap_proxy_balancer_get_best_worker_fn) {

        ap_log_error(APLOG_MARK, APLOG_EMERG, 0, s, APLOGNO(10152)

                     "mod_proxy must be loaded for mod_lbmethod_byrequests");

        return !OK;

    }

    return OK;

}

static void register_hook(apr_pool_t *p)

{

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

    ap_hook_post_config(lbmethod_byrequests_post_config, NULL, NULL, APR_HOOK_MIDDLE);

}

AP_DECLARE_MODULE(lbmethod_byrequests) = {

    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 */

};