org.apache.flume.lifecycle.LifecycleAware Maven / Gradle / Ivy
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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.flume.lifecycle;
import org.apache.flume.annotations.InterfaceAudience;
import org.apache.flume.annotations.InterfaceStability;
/**
*
* An interface implemented by any class that has a defined, stateful,
* lifecycle.
*
*
* Implementations of {@link LifecycleAware} conform to a standard method of
* starting, stopping, and reporting their current state. Additionally, this
* interface creates a standard method of communicating failure to perform a
* lifecycle operation to the caller (i.e. via {@link LifecycleException}). It
* is never considered valid to call {@link #start()} or
* {@link #stop()} more than once or to call them in the wrong order.
* While this is not strictly enforced, it may be in the future.
*
*
* Example services may include Flume nodes and the master, but also lower level
* components that can be controlled in a similar manner.
*
*
* Example usage
*
*
* public class MyService implements LifecycleAware {
*
* private LifecycleState lifecycleState;
*
* public MyService() {
* lifecycleState = LifecycleState.IDLE;
* }
*
* @Override
* public void start(Context context) throws LifecycleException,
* InterruptedException {
*
* ...your code does something.
*
* lifecycleState = LifecycleState.START;
* }
*
* @Override
* public void stop(Context context) throws LifecycleException,
* InterruptedException {
*
* try {
* ...you stop services here.
* } catch (SomethingException) {
* lifecycleState = LifecycleState.ERROR;
* }
*
* lifecycleState = LifecycleState.STOP;
* }
*
* @Override
* public LifecycleState getLifecycleState() {
* return lifecycleState;
* }
*
* }
*
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public interface LifecycleAware {
/**
*
* Starts a service or component.
*
*
* Implementations should determine the result of any start logic and effect
* the return value of {@link #getLifecycleState()} accordingly.
*
*
* @throws LifecycleException
* @throws InterruptedException
*/
public void start();
/**
*
* Stops a service or component.
*
*
* Implementations should determine the result of any stop logic and effect
* the return value of {@link #getLifecycleState()} accordingly.
*
*
* @throws LifecycleException
* @throws InterruptedException
*/
public void stop();
/**
*
* Return the current state of the service or component.
*
*/
public LifecycleState getLifecycleState();
}