org.apache.http.impl.client.AIMDBackoffManager Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of httpclient Show documentation
Show all versions of httpclient Show documentation
Apache HttpComponents Client
/*
* ====================================================================
* 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.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* The AIMDBackoffManager applies an additive increase,
* multiplicative decrease (AIMD) to managing a dynamic limit to
* the number of connections allowed to a given host. You may want
* to experiment with the settings for the cooldown periods and the
* backoff factor to get the adaptive behavior you want.
*
* Generally speaking, shorter cooldowns will lead to more steady-state
* variability but faster reaction times, while longer cooldowns
* will lead to more stable equilibrium behavior but slower reaction
* times.
*
* Similarly, higher backoff factors promote greater
* utilization of available capacity at the expense of fairness
* among clients. Lower backoff factors allow equal distribution of
* capacity among clients (fairness) to happen faster, at the
* expense of having more server capacity unused in the short term.
*
* @since 4.2
*/
public class AIMDBackoffManager implements BackoffManager {
private final ConnPoolControl connPerRoute;
private final Clock clock;
private final Map lastRouteProbes;
private final Map lastRouteBackoffs;
private long coolDown = 5 * 1000L;
private double backoffFactor = 0.5;
private int cap = 2; // Per RFC 2616 sec 8.1.4
/**
* Creates an AIMDBackoffManager to manage
* per-host connection pool sizes represented by the
* given {@link ConnPoolControl}.
* @param connPerRoute per-host routing maximums to
* be managed
*/
public AIMDBackoffManager(final ConnPoolControl connPerRoute) {
this(connPerRoute, new SystemClock());
}
AIMDBackoffManager(final ConnPoolControl connPerRoute, final Clock clock) {
this.clock = clock;
this.connPerRoute = connPerRoute;
this.lastRouteProbes = new HashMap();
this.lastRouteBackoffs = new HashMap();
}
public void backOff(final HttpRoute route) {
synchronized(connPerRoute) {
final int curr = connPerRoute.getMaxPerRoute(route);
final Long lastUpdate = getLastUpdate(lastRouteBackoffs, route);
final long now = clock.getCurrentTime();
if (now - lastUpdate.longValue() < coolDown) {
return;
}
connPerRoute.setMaxPerRoute(route, getBackedOffPoolSize(curr));
lastRouteBackoffs.put(route, Long.valueOf(now));
}
}
private int getBackedOffPoolSize(final int curr) {
if (curr <= 1) {
return 1;
}
return (int)(Math.floor(backoffFactor * curr));
}
public void probe(final HttpRoute route) {
synchronized(connPerRoute) {
final int curr = connPerRoute.getMaxPerRoute(route);
final int max = (curr >= cap) ? cap : curr + 1;
final Long lastProbe = getLastUpdate(lastRouteProbes, route);
final Long lastBackoff = getLastUpdate(lastRouteBackoffs, route);
final long now = clock.getCurrentTime();
if (now - lastProbe.longValue() < coolDown || now - lastBackoff.longValue() < coolDown) {
return;
}
connPerRoute.setMaxPerRoute(route, max);
lastRouteProbes.put(route, Long.valueOf(now));
}
}
private Long getLastUpdate(final Map updates, final HttpRoute route) {
Long lastUpdate = updates.get(route);
if (lastUpdate == null) {
lastUpdate = Long.valueOf(0L);
}
return lastUpdate;
}
/**
* Sets the factor to use when backing off; the new
* per-host limit will be roughly the current max times
* this factor. Math.floor is applied in the
* case of non-integer outcomes to ensure we actually
* decrease the pool size. Pool sizes are never decreased
* below 1, however. Defaults to 0.5.
* @param d must be between 0.0 and 1.0, exclusive.
*/
public void setBackoffFactor(final double d) {
Args.check(d > 0.0 && d < 1.0, "Backoff factor must be 0.0 < f < 1.0");
backoffFactor = d;
}
/**
* Sets the amount of time, in milliseconds, to wait between
* adjustments in pool sizes for a given host, to allow
* enough time for the adjustments to take effect. Defaults
* to 5000L (5 seconds).
* @param l must be positive
*/
public void setCooldownMillis(final long l) {
Args.positive(coolDown, "Cool down");
coolDown = l;
}
/**
* Sets the absolute maximum per-host connection pool size to
* probe up to; defaults to 2 (the default per-host max).
* @param cap must be >= 1
*/
public void setPerHostConnectionCap(final int cap) {
Args.positive(cap, "Per host connection cap");
this.cap = cap;
}
}