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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.
* ====================================================================
*
* 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 {@code 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 {@code 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();
}
@Override
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));
}
@Override
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. {@code 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;
}
}