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* JBoss, Home of Professional Open Source.
* Copyright 2017 Red Hat, Inc., and individual contributors
* as indicated by the @author tags.
*
* Licensed 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.
*/
package org.jboss.ejb.client;
import java.net.URI;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicInteger;
import org.wildfly.common.Assert;
/**
* A selector which selects and returns a URI, from among the passed eligible URIs, that can handle a specific
* deployment within a EJB client context. Typical usage of {@link DiscoveredURISelector} involves load balancing
* calls to multiple targets which can all handle the same deployment. This allows the application to have a deterministic
* target selection policy while dealing with multiple targets with same deployment.
*
* Target selection is only used when discovery yields more than one URI as a result of its query to locate an EJB.
*
* @author David M. Lloyd
* @author Jaikiran Pai
*/
public interface DiscoveredURISelector {
/**
* Selects and returns a URI from among the {@code eligibleUris} to handle the invocation on a deployment
* represented by the passed in {@code locator}. Implementations of this method must not return
* {@code null} or any other node name which isn't in the {@code eligibleUris} list.
*
* Note that the list sent in for {@code eligibleUris} is indexed, meaning that the {@code contains} operation
* is guaranteed to run in constant time.
*
* @param eligibleUris an indexed list of the eligible nodes which can handle the deployment; not {@code null}, will not be empty
* @param locator the locator of the EJB being invoked upon
* @return the URI selection (must not be {@code null}, must be one of the URIs from {@code eligibleUris})
*/
URI selectNode(final List eligibleUris, final EJBLocator locator);
/**
* Create a deployment URI selector that prefers one or more favorite nodes, falling back to another selector if
* none of the favorites are found.
*
* @param favorites the favorite nodes, in decreasing order of preference (must not be {@code null})
* @param fallback the fallback selector (must not be {@code null})
* @return the selector (not {@code null})
*/
static DiscoveredURISelector favorite(Collection favorites, DiscoveredURISelector fallback) {
Assert.checkNotNullParam("favorites", favorites);
Assert.checkNotNullParam("fallback", fallback);
return (eligibleUris, locator) -> {
for (URI favorite : favorites) {
if (eligibleUris.contains(favorite)) {
return favorite;
}
}
return fallback.selectNode(eligibleUris, locator);
};
}
/**
* A deployment URI selector which prefers the first URI always. This will generally avoid load balancing in most
* cases.
*/
DiscoveredURISelector FIRST = (eligibleUris, locator) -> eligibleUris.iterator().next();
/**
* A deployment URI selector which randomly chooses the next URI. This will generally provide the best possible
* load balancing over a large number of requests.
*/
DiscoveredURISelector RANDOM = (eligibleUris, locator) -> eligibleUris.get(ThreadLocalRandom.current().nextInt(eligibleUris.size()));
/**
* A deployment URI selector which uses an approximate round-robin policy among all of the eligible URIs. Note
* that the round-robin URI count may be shared among multiple node sets, thus certain specific usage patterns
* may defeat the round-robin behavior.
*/
DiscoveredURISelector ROUND_ROBIN = new DiscoveredURISelector() {
private final AtomicInteger counter = new AtomicInteger();
public URI selectNode(final List eligibleUris, final EJBLocator locator) {
final int length = eligibleUris.size();
assert length > 0;
return eligibleUris.get(Math.floorMod(counter.getAndIncrement(), length));
}
};
}