| /** |
| * 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 backtype.storm.spout; |
| |
| import backtype.storm.task.TopologyContext; |
| import java.util.Map; |
| import java.io.Serializable; |
| |
| /** |
| * ISpout is the core interface for implementing spouts. A Spout is responsible for feeding messages into the topology for processing. For every tuple emitted |
| * by a spout, Storm will track the (potentially very large) DAG of tuples generated based on a tuple emitted by the spout. When Storm detects that every tuple |
| * in that DAG has been successfully processed, it will send an ack message to the Spout. |
| * |
| * <p> |
| * If a tuple fails to be fully processed within the configured timeout for the topology (see {@link backtype.storm.Config}), Storm will send a fail message to |
| * the spout for the message. |
| * </p> |
| * |
| * <p> |
| * When a Spout emits a tuple, it can tag the tuple with a message id. The message id can be any type. When Storm acks or fails a message, it will pass back to |
| * the spout the same message id to identify which tuple it's referring to. If the spout leaves out the message id, or sets it to null, then Storm will not |
| * track the message and the spout will not receive any ack or fail callbacks for the message. |
| * </p> |
| * |
| * <p> |
| * Storm executes ack, fail, and nextTuple all on the same thread. This means that an implementor of an ISpout does not need to worry about concurrency issues |
| * between those methods. However, it also means that an implementor must ensure that nextTuple is non-blocking: otherwise the method could block acks and fails |
| * that are pending to be processed. |
| * </p> |
| */ |
| public interface ISpout extends Serializable { |
| /** |
| * Called when a task for this component is initialized within a worker on the cluster. It provides the spout with the environment in which the spout |
| * executes. |
| * |
| * <p> |
| * This includes the: |
| * </p> |
| * |
| * @param conf The Storm configuration for this spout. This is the configuration provided to the topology merged in with cluster configuration on this |
| * machine. |
| * @param context This object can be used to get information about this task's place within the topology, including the task id and component id of this |
| * task, input and output information, etc. |
| * @param collector The collector is used to emit tuples from this spout. Tuples can be emitted at any time, including the open and close methods. The |
| * collector is thread-safe and should be saved as an instance variable of this spout object. |
| */ |
| void open(Map conf, TopologyContext context, SpoutOutputCollector collector); |
| |
| /** |
| * Called when an ISpout is going to be shutdown. There is no guarentee that close will be called, because the supervisor kill -9's worker processes on the |
| * cluster. |
| * |
| * <p> |
| * The one context where close is guaranteed to be called is a topology is killed when running Storm in local mode. |
| * </p> |
| */ |
| void close(); |
| |
| /** |
| * Called when a spout has been activated out of a deactivated mode. nextTuple will be called on this spout soon. A spout can become activated after having |
| * been deactivated when the topology is manipulated using the `storm` client. |
| */ |
| void activate(); |
| |
| /** |
| * Called when a spout has been deactivated. nextTuple will not be called while a spout is deactivated. The spout may or may not be reactivated in the |
| * future. |
| */ |
| void deactivate(); |
| |
| /** |
| * When this method is called, Storm is requesting that the Spout emit tuples to the output collector. This method should be non-blocking, so if the Spout |
| * has no tuples to emit, this method should return. nextTuple, ack, and fail are all called in a tight loop in a single thread in the spout task. When |
| * there are no tuples to emit, it is courteous to have nextTuple sleep for a short amount of time (like a single millisecond) so as not to waste too much |
| * CPU. |
| */ |
| void nextTuple(); |
| |
| /** |
| * Storm has determined that the tuple emitted by this spout with the msgId identifier has been fully processed. Typically, an implementation of this method |
| * will take that message off the queue and prevent it from being replayed. |
| */ |
| void ack(Object msgId); |
| |
| /** |
| * The tuple emitted by this spout with the msgId identifier has failed to be fully processed. Typically, an implementation of this method will put that |
| * message back on the queue to be replayed at a later time. |
| */ |
| void fail(Object msgId); |
| } |