/*
* Copyright 2014, Stratio.
*
* 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 com.stratio.deep.cassandra.cql;
import java.net.InetAddress;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicInteger;
import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.Host;
import com.datastax.driver.core.HostDistance;
import com.datastax.driver.core.Statement;
import com.datastax.driver.core.policies.RoundRobinPolicy;
import com.google.common.collect.AbstractIterator;
/**
* Load balancing policy that, unlike round robin, sticks to one host.
*/
public class LocalMachineLoadBalancingPolicy extends RoundRobinPolicy {
private InetAddress host;
/**
* Public constructor.
*/
public LocalMachineLoadBalancingPolicy(InetAddress host) {
this.host = host;
}
private final CopyOnWriteArrayList<Host> liveHosts = new CopyOnWriteArrayList<Host>();
private final AtomicInteger index = new AtomicInteger();
/**
* {@inheritDoc}
*/
@Override
public void init(Cluster cluster, Collection<Host> hosts) {
for (Host h : hosts) {
if (h.getAddress().equals(host)) {
this.liveHosts.add(h);
this.index.set(0);
break;
}
}
}
/**
* Return the HostDistance for the provided host.
* <p/>
* This policy consider all nodes as local. This is generally the right
* thing to do in a single datacenter deployment. If you use multiple
* datacenter, see {@link com.datastax.driver.core.policies.DCAwareRoundRobinPolicy} instead.
*
* @param host the host of which to return the distance of.
* @return the HostDistance to {@code host}.
*/
@Override
public HostDistance distance(Host host) {
return HostDistance.LOCAL;
}
/**
* Returns the hosts to use for a new query.
* <p/>
* The returned plan will try each known host of the cluster. Upon each
* call to this method, the {@code i}th host of the plans returned will cycle
* over all the hosts of the cluster in a round-robin fashion.
*
* @param loggedKeyspace the keyspace currently logged in on for this
* query.
* @param statement the query for which to build the plan.
* @return a new query plan, i.e. an iterator indicating which host to
* try first for querying, which one to use as failover, etc...
*/
@Override
public Iterator<Host> newQueryPlan(String loggedKeyspace, Statement statement) {
// We clone liveHosts because we want a version of the list that
// cannot change concurrently of the query plan iterator (this
// would be racy). We use clone() as it don't involve a copy of the
// underlying array (and thus we rely on liveHosts being a CopyOnWriteArrayList).
@SuppressWarnings("unchecked")
final List<Host> hosts = (List<Host>) liveHosts.clone();
final int startIdx = index.getAndIncrement();
// Overflow protection; not theoretically thread safe but should be good enough
if (startIdx > Integer.MAX_VALUE - 10000) {
index.set(0);
}
return new AbstractIterator<Host>() {
private int idx = startIdx;
private int remaining = hosts.size();
@Override
protected Host computeNext() {
if (remaining <= 0) {
return endOfData();
}
remaining--;
int c = idx++ % hosts.size();
if (c < 0) {
c += hosts.size();
}
return hosts.get(c);
}
};
}
/**
* {@inheritDoc}
*/
@Override
public void onUp(Host host) {
liveHosts.addIfAbsent(host);
}
/**
* {@inheritDoc}
*/
@Override
public void onDown(Host host) {
liveHosts.remove(host);
}
/**
* Adds the given new host only if the list of known hosts is empty.
*
* @param host the host to add.
*/
@Override
public void onAdd(Host host) {
if (liveHosts.isEmpty()) {
onUp(host);
}
}
/**
* {@inheritDoc}
*/
@Override
public void onRemove(Host host) {
onDown(host);
}
}