1/**
2 * Copyright (C) 2010 Google Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.inject.service;
18
19import java.util.concurrent.ExecutionException;
20import java.util.concurrent.Future;
21
22/**
23 * An object with an operational state, asynchronous {@link #start()} and
24 * {@link #stop()} lifecycle methods to transition in and out of this state.
25 * Example services include http servers, RPC systems and timer tasks.
26 *
27 * @author dhanji@gmail.com (Dhanji R. Prasanna)
28 */
29public interface Service {
30  /**
31   * If the service has already been started, this method returns
32   * immediately without taking action. A stopped service may not be restarted.
33   *
34   * @return a future for the startup result, regardless of whether this call
35   *     initiated startup. Calling {@link Future#get} will block until the
36   *     service has finished starting, and returns the resultant state. If
37   *     the service fails to start, {@link Future#get} will throw an {@link
38   *     ExecutionException}. If it has already finished starting,
39   *     {@link Future#get} returns immediately.
40   */
41  Future<State> start();
42
43  /**
44   * If the service is {@link State#STARTED} initiates service shutdown and
45   * returns immediately. If the service has already been stopped, this
46   * method returns immediately without taking action.
47   *
48   * @return a future for the shutdown result, regardless of whether this call
49   *     initiated shutdown. Calling {@link Future#get} will block until the
50   *     service has finished shutting down, and either returns {@link
51   *     State#STOPPED} or throws an {@link ExecutionException}. If it has
52   *     already finished stopping, {@link Future#get} returns immediately.
53   */
54  Future<State> stop();
55
56  /**
57   * Returns the current state of this service. One of {@link State} possible
58   * values, or null if this is a brand new object, i.e., has not been put into
59   * any state yet.
60   */
61  State state();
62
63  /**
64   * The lifecycle states of a service.
65   */
66  enum State { STARTED, STOPPED, FAILED }
67}
68