cassandra-trunk/src/java/org/apache/cassandra/schema/SchemaPushVerbHandler.java
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.cassandra.schema;

import java.util.Collection;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.function.Consumer;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.cassandra.db.Mutation;
import org.apache.cassandra.net.IVerbHandler;
import org.apache.cassandra.net.Message;

/**
 * Called when node receives updated schema state from the schema migration coordinator node.
 * Such happens when user makes local schema migration on one of the nodes in the ring
 * (which is going to act as coordinator) and that node sends (pushes) it's updated schema state
 * (in form of mutations) to all the alive nodes in the cluster.
 */
public final class SchemaPushVerbHandler implements IVerbHandler<Collection<Mutation>>
{
    public static final SchemaPushVerbHandler instance = new SchemaPushVerbHandler();

    private static final Logger logger = LoggerFactory.getLogger(SchemaPushVerbHandler.class);

    private final List<Consumer<Message<Collection<Mutation>>>> handlers = new CopyOnWriteArrayList<>();

    public void register(Consumer<Message<Collection<Mutation>>> handler)
    {
        handlers.add(handler);
    }

    public void doVerb(final Message<Collection<Mutation>> message)
    {
        logger.trace("Received schema push request from {}", message.from());
        SchemaAnnouncementDiagnostics.schemataMutationsReceived(message.from());

        List<Consumer<Message<Collection<Mutation>>>> handlers = this.handlers;
        if (handlers.isEmpty())
            throw new UnsupportedOperationException("There is no handler registered for schema push verb");

        handlers.forEach(h -> h.accept(message));
    }
}
