org.apache.twill.internal.ZKMessages.java Source code

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Here is the source code for org.apache.twill.internal.ZKMessages.java

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/*
 * 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.twill.internal;

import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import org.apache.twill.internal.state.Message;
import org.apache.twill.internal.state.MessageCodec;
import org.apache.twill.zookeeper.ZKClient;
import org.apache.twill.zookeeper.ZKOperations;
import org.apache.zookeeper.CreateMode;

/**
 * Helper class to send messages to remote instances using Apache Zookeeper watch mechanism.
 */
public final class ZKMessages {

    /**
     * Creates a message node in zookeeper. The message node created is a PERSISTENT_SEQUENTIAL node.
     *
     * @param zkClient The ZooKeeper client for interacting with ZooKeeper.
     * @param messagePathPrefix ZooKeeper path prefix for the message node.
     * @param message The {@link Message} object for the content of the message node.
     * @param completionResult Object to set to the result future when the message is processed.
     * @param <V> Type of the completion result.
     * @return A {@link ListenableFuture} that will be completed when the message is consumed, which indicated
     *         by deletion of the node. If there is exception during the process, it will be reflected
     *         to the future returned.
     */
    public static <V> ListenableFuture<V> sendMessage(final ZKClient zkClient, String messagePathPrefix,
            Message message, final V completionResult) {
        SettableFuture<V> result = SettableFuture.create();
        sendMessage(zkClient, messagePathPrefix, message, result, completionResult);
        return result;
    }

    /**
     * Creates a message node in zookeeper. The message node created is a PERSISTENT_SEQUENTIAL node.
     *
     * @param zkClient The ZooKeeper client for interacting with ZooKeeper.
     * @param messagePathPrefix ZooKeeper path prefix for the message node.
     * @param message The {@link Message} object for the content of the message node.
     * @param completion A {@link SettableFuture} to reflect the result of message process completion.
     * @param completionResult Object to set to the result future when the message is processed.
     * @param <V> Type of the completion result.
     */
    public static <V> void sendMessage(final ZKClient zkClient, String messagePathPrefix, Message message,
            final SettableFuture<V> completion, final V completionResult) {

        // Creates a message and watch for its deletion for completion.
        Futures.addCallback(
                zkClient.create(messagePathPrefix, MessageCodec.encode(message), CreateMode.PERSISTENT_SEQUENTIAL),
                new FutureCallback<String>() {
                    @Override
                    public void onSuccess(String path) {
                        Futures.addCallback(ZKOperations.watchDeleted(zkClient, path),
                                new FutureCallback<String>() {
                                    @Override
                                    public void onSuccess(String result) {
                                        completion.set(completionResult);
                                    }

                                    @Override
                                    public void onFailure(Throwable t) {
                                        completion.setException(t);
                                    }
                                });
                    }

                    @Override
                    public void onFailure(Throwable t) {
                        completion.setException(t);
                    }
                });
    }

    private ZKMessages() {
    }
}