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/* 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 */
};
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