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1   /*
2    * ====================================================================
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *   http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing,
14   * software distributed under the License is distributed on an
15   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16   * KIND, either express or implied.  See the License for the
17   * specific language governing permissions and limitations
18   * under the License.
19   * ====================================================================
20   *
21   * This software consists of voluntary contributions made by many
22   * individuals on behalf of the Apache Software Foundation.  For more
23   * information on the Apache Software Foundation, please see
24   * <http://www.apache.org/>.
25   *
26   */
27  package org.apache.http.impl.client;
28  
29  import java.util.HashMap;
30  import java.util.Map;
31  
32  import org.apache.http.client.BackoffManager;
33  import org.apache.http.conn.routing.HttpRoute;
34  import org.apache.http.pool.ConnPoolControl;
35  import org.apache.http.util.Args;
36  
37  /**
38   * <p>The {@code AIMDBackoffManager} applies an additive increase,
39   * multiplicative decrease (AIMD) to managing a dynamic limit to
40   * the number of connections allowed to a given host. You may want
41   * to experiment with the settings for the cooldown periods and the
42   * backoff factor to get the adaptive behavior you want.</p>
43   *
44   * <p>Generally speaking, shorter cooldowns will lead to more steady-state
45   * variability but faster reaction times, while longer cooldowns
46   * will lead to more stable equilibrium behavior but slower reaction
47   * times.</p>
48   *
49   * <p>Similarly, higher backoff factors promote greater
50   * utilization of available capacity at the expense of fairness
51   * among clients. Lower backoff factors allow equal distribution of
52   * capacity among clients (fairness) to happen faster, at the
53   * expense of having more server capacity unused in the short term.</p>
54   *
55   * @since 4.2
56   */
57  public class AIMDBackoffManager implements BackoffManager {
58  
59      private final ConnPoolControl<HttpRoute> connPerRoute;
60      private final Clock clock;
61      private final Map<HttpRoute,Long> lastRouteProbes;
62      private final Map<HttpRoute,Long> lastRouteBackoffs;
63      private long coolDown = 5 * 1000L;
64      private double backoffFactor = 0.5;
65      private int cap = 2; // Per RFC 2616 sec 8.1.4
66  
67      /**
68       * Creates an {@code AIMDBackoffManager} to manage
69       * per-host connection pool sizes represented by the
70       * given {@link ConnPoolControl}.
71       * @param connPerRoute per-host routing maximums to
72       *   be managed
73       */
74      public AIMDBackoffManager(final ConnPoolControl<HttpRoute> connPerRoute) {
75          this(connPerRoute, new SystemClock());
76      }
77  
78      AIMDBackoffManager(final ConnPoolControl<HttpRoute> connPerRoute, final Clock clock) {
79          this.clock = clock;
80          this.connPerRoute = connPerRoute;
81          this.lastRouteProbes = new HashMap<HttpRoute,Long>();
82          this.lastRouteBackoffs = new HashMap<HttpRoute,Long>();
83      }
84  
85      @Override
86      public void backOff(final HttpRoute route) {
87          synchronized(connPerRoute) {
88              final int curr = connPerRoute.getMaxPerRoute(route);
89              final Long lastUpdate = getLastUpdate(lastRouteBackoffs, route);
90              final long now = clock.getCurrentTime();
91              if (now - lastUpdate.longValue() < coolDown) {
92                  return;
93              }
94              connPerRoute.setMaxPerRoute(route, getBackedOffPoolSize(curr));
95              lastRouteBackoffs.put(route, Long.valueOf(now));
96          }
97      }
98  
99      private int getBackedOffPoolSize(final int curr) {
100         if (curr <= 1) {
101             return 1;
102         }
103         return (int)(Math.floor(backoffFactor * curr));
104     }
105 
106     @Override
107     public void probe(final HttpRoute route) {
108         synchronized(connPerRoute) {
109             final int curr = connPerRoute.getMaxPerRoute(route);
110             final int max = (curr >= cap) ? cap : curr + 1;
111             final Long lastProbe = getLastUpdate(lastRouteProbes, route);
112             final Long lastBackoff = getLastUpdate(lastRouteBackoffs, route);
113             final long now = clock.getCurrentTime();
114             if (now - lastProbe.longValue() < coolDown || now - lastBackoff.longValue() < coolDown) {
115                 return;
116             }
117             connPerRoute.setMaxPerRoute(route, max);
118             lastRouteProbes.put(route, Long.valueOf(now));
119         }
120     }
121 
122     private Long getLastUpdate(final Map<HttpRoute,Long> updates, final HttpRoute route) {
123         Long lastUpdate = updates.get(route);
124         if (lastUpdate == null) {
125             lastUpdate = Long.valueOf(0L);
126         }
127         return lastUpdate;
128     }
129 
130     /**
131      * Sets the factor to use when backing off; the new
132      * per-host limit will be roughly the current max times
133      * this factor. {@code Math.floor} is applied in the
134      * case of non-integer outcomes to ensure we actually
135      * decrease the pool size. Pool sizes are never decreased
136      * below 1, however. Defaults to 0.5.
137      * @param d must be between 0.0 and 1.0, exclusive.
138      */
139     public void setBackoffFactor(final double d) {
140         Args.check(d > 0.0 && d < 1.0, "Backoff factor must be 0.0 < f < 1.0");
141         backoffFactor = d;
142     }
143 
144     /**
145      * Sets the amount of time, in milliseconds, to wait between
146      * adjustments in pool sizes for a given host, to allow
147      * enough time for the adjustments to take effect. Defaults
148      * to 5000L (5 seconds).
149      * @param l must be positive
150      */
151     public void setCooldownMillis(final long l) {
152         Args.positive(coolDown, "Cool down");
153         coolDown = l;
154     }
155 
156     /**
157      * Sets the absolute maximum per-host connection pool size to
158      * probe up to; defaults to 2 (the default per-host max).
159      * @param cap must be &gt;= 1
160      */
161     public void setPerHostConnectionCap(final int cap) {
162         Args.positive(cap, "Per host connection cap");
163         this.cap = cap;
164     }
165 
166 }