/*
* Copyright © 2014 Cask Data, Inc.
*
* 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 co.cask.cdap.common.discovery;
import org.apache.twill.discovery.Discoverable;
import java.util.Iterator;
import java.util.Random;
/**
* Randomly picks endpoint from the list of available endpoints.
*/
public final class RandomEndpointStrategy implements EndpointStrategy {
private final Iterable<Discoverable> endpoints;
/**
* Constructs a random endpoint strategy.
* @param endpoints Endpoints for the strategy to use. Note that this strategy will
* invoke {@link Iterable#iterator()} and traverse through it on
* every call to the {@link #pick()} method. One could leverage this
* behavior with the live {@link Iterable} as provided by
* {@link org.apache.twill.discovery.DiscoveryServiceClient#discover(String)} method.
*/
public RandomEndpointStrategy(Iterable<Discoverable> endpoints) {
this.endpoints = endpoints;
}
@Override
public Discoverable pick() {
// Reservoir sampling
Discoverable result = null;
Iterator<Discoverable> itor = endpoints.iterator();
Random random = new Random();
int count = 0;
while (itor.hasNext()) {
Discoverable next = itor.next();
if (random.nextInt(++count) == 0) {
result = next;
}
}
return result;
}
}