apache/modules/proxy/examples/mod_lbmethod_rr.c

   1 /* Licensed to the Apache Software Foundation (ASF) under one or more
   2  * contributor license agreements.  See the NOTICE file distributed with
   3  * this work for additional information regarding copyright ownership.
   4  * The ASF licenses this file to You under the Apache License, Version 2.0
   5  * (the "License"); you may not use this file except in compliance with
   6  * the License.  You may obtain a copy of the License at
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 /* Round Robin lbmethod EXAMPLE module for Apache proxy */
  18
  19 /* NOTE: This is designed simply to provide some info on how to create
  20          extra lbmethods via sub-modules... This code is ugly
  21          and needs work to actually do round-robin "right"
  22          but that is left as an exercise for the reader */
  23
  24 #include "mod_proxy.h"
  25 #include "scoreboard.h"
  26 #include "ap_mpm.h"
  27 #include "apr_version.h"
  28 #include "apr_hooks.h"
  29
  30 #if APR_HAVE_UNISTD_H
  31 #include <unistd.h> /* for getpid() */
  32 #endif
  33
  34 module AP_MODULE_DECLARE_DATA proxy_balancer_rr_module;
  35
  36 typedef struct {
  37     int index;
  38 } rr_data ;
  39
  40 /*
  41  */
  42 static proxy_worker *find_best_roundrobin(proxy_balancer *balancer,
  43                                          request_rec *r)
  44 {
  45     int i;
  46     proxy_worker *worker;
  47     proxy_worker *mycandidate = NULL;
  48     int checking_standby;
  49     int checked_standby;
  50     rr_data *ctx;
  51
  52     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
  53                  "proxy: Entering roundrobin for BALANCER %s (%d)",
  54                  balancer->name, (int)getpid());
  55
  56     /* The index of the candidate last chosen is stored in ctx->index */
  57     if (!balancer->context) {
  58         /* UGLY */
  59         ctx = apr_pcalloc(r->server->process->pconf, sizeof(rr_data));
  60         balancer->context = (void *)ctx;
  61         ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
  62                  "proxy: Creating roundrobin ctx for BALANCER %s (%d)",
  63                  balancer->name, (int)getpid());
  64     } else {
  65         ctx = (rr_data *)balancer->context;
  66     }
  67     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
  68                  "proxy: roundrobin index: %d (%d)",
  69                  ctx->index, (int)getpid());
  70
  71     checking_standby = checked_standby = 0;
  72     while (!mycandidate && !checked_standby) {
  73         worker = (proxy_worker *)balancer->workers->elts;
  74
  75         for (i = 0; i < balancer->workers->nelts; i++, worker++) {
  76             if (i < ctx->index)
  77                 continue;
  78             if ( (checking_standby ? !PROXY_WORKER_IS_STANDBY(worker) : PROXY_WORKER_IS_STANDBY(worker)) )
  79                 continue;
  80             if (!PROXY_WORKER_IS_USABLE(worker))
  81                 ap_proxy_retry_worker("BALANCER", worker, r->server);
  82             if (PROXY_WORKER_IS_USABLE(worker)) {
  83                 mycandidate = worker;
  84                 break;
  85             }
  86         }
  87         checked_standby = checking_standby++;
  88     }
  89
  90
  91     ctx->index += 1;
  92     if (ctx->index >= balancer->workers->nelts) {
  93         ctx->index = 0;
  94     }
  95     return mycandidate;
  96 }
  97
  98 static const proxy_balancer_method roundrobin =
  99 {
 100     "roundrobin",
 101     &find_best_roundrobin,
 102     NULL
 103 };
 104
 105
 106 static void ap_proxy_rr_register_hook(apr_pool_t *p)
 107 {
 108     ap_register_provider(p, PROXY_LBMETHOD, "roundrobin", "0", &roundrobin);
 109 }
 110
 111 module AP_MODULE_DECLARE_DATA proxy_balancer_rr_module = {
 112     STANDARD20_MODULE_STUFF,
 113     NULL,       /* create per-directory config structure */
 114     NULL,       /* merge per-directory config structures */
 115     NULL,       /* create per-server config structure */
 116     NULL,       /* merge per-server config structures */
 117     NULL,       /* command apr_table_t */
 118     ap_proxy_rr_register_hook /* register hooks */
 119 };