activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/client/impl/ServerLocatorImpl.java
public final class ServerLocatorImpl implements ServerLocatorInternal, DiscoveryListener {
//…
private TransportConfiguration selectConnector() {
Pair<TransportConfiguration, TransportConfiguration>[] usedTopology;
flushTopology();
synchronized (topologyArrayGuard) {
usedTopology = topologyArray;
}
synchronized (this) {
if (usedTopology != null && useTopologyForLoadBalancing) {
if (logger.isTraceEnabled()) {
logger.trace("Selecting connector from topology.");
}
int pos = loadBalancingPolicy.select(usedTopology.length);
Pair<TransportConfiguration, TransportConfiguration> pair = usedTopology[pos];
return pair.getA();
} else {
if (logger.isTraceEnabled()) {
logger.trace("Selecting connector from initial connectors.");
}
int pos = loadBalancingPolicy.select(initialConnectors.length);
return initialConnectors[pos];
}
}
}
//…
}
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ServerLocatorImpl的selectConnector方法会对于useTopologyForLoadBalancing的会通过loadBalancingPolicy.select(usedTopology.length)来获取pos，之后返回usedTopology[pos].getA()；否则通过loadBalancingPolicy.select(initialConnectors.length)获取pos，之后返回initialConnectors[pos]
ConnectionLoadBalancingPolicy
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/api/core/client/loadbalance/ConnectionLoadBalancingPolicy.java
public interface ConnectionLoadBalancingPolicy {
/**
* Returns the selected index according to the policy implementation.
*
* @param max maximum position index that can be selected
*/
int select(int max);
}
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ConnectionLoadBalancingPolicy定义了select接口，返回选中的index；它有四个实现类分别是FirstElementConnectionLoadBalancingPolicy、RandomConnectionLoadBalancingPolicy、RoundRobinConnectionLoadBalancingPolicy、RandomStickyConnectionLoadBalancingPolicy
FirstElementConnectionLoadBalancingPolicy
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/api/core/client/loadbalance/FirstElementConnectionLoadBalancingPolicy.java
public final class FirstElementConnectionLoadBalancingPolicy implements ConnectionLoadBalancingPolicy {
/**
* @param max param is ignored
* @return 0
*/
@Override
public int select(final int max) {
return 0;
}
}
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FirstElementConnectionLoadBalancingPolicy实现了ConnectionLoadBalancingPolicy接口，其select方法始终返回0
RandomConnectionLoadBalancingPolicy
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/api/core/client/loadbalance/RandomConnectionLoadBalancingPolicy.java
public final class RandomConnectionLoadBalancingPolicy implements ConnectionLoadBalancingPolicy {
/**
* Returns a pseudo random number between {@code 0} (inclusive) and {@code max} exclusive.
*
* @param max the upper limit of the random number selection
* @see java.util.Random#nextInt(int)
*/
@Override
public int select(final int max) {
return RandomUtil.randomInterval(0, max);
}
}
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RandomConnectionLoadBalancingPolicy实现了ConnectionLoadBalancingPolicy接口，其select方法使用RandomUtil.randomInterval(0, max)随机返回一个index
RoundRobinConnectionLoadBalancingPolicy
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/api/core/client/loadbalance/RoundRobinConnectionLoadBalancingPolicy.java
public final class RoundRobinConnectionLoadBalancingPolicy implements ConnectionLoadBalancingPolicy, Serializable {
private static final long serialVersionUID = 7511196010141439559L;
private boolean first = true;
private int pos;
@Override
public int select(final int max) {
if (first) {
// We start on a random one
pos = RandomUtil.randomInterval(0, max);
first = false;
} else {
pos++;
if (pos >= max) {
pos = 0;
}
}
return pos;
}
}
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RoundRobinConnectionLoadBalancingPolicy实现了ConnectionLoadBalancingPolicy接口，其select在第一次执行的时候随机选择一个pos，之后对pos递增，对于递增之后大于等于max的重置pos为0
RandomStickyConnectionLoadBalancingPolicy
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/api/core/client/loadbalance/RandomStickyConnectionLoadBalancingPolicy.java
public final class RandomStickyConnectionLoadBalancingPolicy implements ConnectionLoadBalancingPolicy {
private int pos = -1;
/**
* @see java.util.Random#nextInt(int)
*/
@Override
public int select(final int max) {
if (pos == -1) {
pos = RandomUtil.randomInterval(0, max);
}
return pos;
}
}
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RandomStickyConnectionLoadBalancingPolicy实现了ConnectionLoadBalancingPolicy接口，其select方法第一次随机选择一个pos，之后都返回该pos
小结
ConnectionLoadBalancingPolicy定义了select接口，返回选中的index；它有四个实现类分别是FirstElementConnectionLoadBalancingPolicy、RandomConnectionLoadBalancingPolicy、RoundRobinConnectionLoadBalancingPolicy、RandomStickyConnectionLoadBalancingPolicy
