/*
* 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;
/**
* An {@link EndpointStrategy} that will always return the same endpoint once it's picked
* until the endpoint is no longer valid, then it'll pick another one.
*
* If multiple threads calling the {@link #pick()}} method at the same time, it's possible
* that they get different result if there was no endpoint being picked yet or the previously
* picked endpoint is no longer value. The pick will be eventually settled to the same one.
*/
public final class StickyEndpointStrategy implements EndpointStrategy {
private final Iterable<Discoverable> discoverables;
private final EndpointStrategy picker;
private volatile Discoverable lastPick;
public StickyEndpointStrategy(Iterable<Discoverable> discoverables) {
this.discoverables = discoverables;
this.picker = new RandomEndpointStrategy(discoverables);
}
@Override
public Discoverable pick() {
Discoverable lastPick = this.lastPick;
if (lastPick == null || !isValid(lastPick)) {
this.lastPick = lastPick = picker.pick();
}
return lastPick;
}
private boolean isValid(Discoverable endpoint) {
for (Discoverable discoverable : discoverables) {
if (discoverable.getSocketAddress().equals(endpoint.getSocketAddress())) {
return true;
}
}
return false;
}
}