AbstractIdleService.java revision 7dd252788645e940eada959bdde927426e2531c9 
1/*
2 * Copyright (C) 2009 The Guava Authors
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.common.util.concurrent;
18
19import com.google.common.annotations.Beta;
20import com.google.common.base.Throwables;
21
22import java.util.concurrent.Executor;
23
24/**
25 * Base class for services that do not need a thread while "running"
26 * but may need one during startup and shutdown. Subclasses can
27 * implement {@link #startUp} and {@link #shutDown} methods, each
28 * which run in a executor which by default uses a separate thread
29 * for each method.
30 *
31 * @author Chris Nokleberg
32 * @since 1.0
33 */
34@Beta
35public abstract class AbstractIdleService implements Service {
36
37  /* use AbstractService for state management */
38  private final Service delegate = new AbstractService() {
39    @Override
40    protected final void doStart() {
41      executor().execute(new Runnable() {
42        public void run() {
43          try {
44            startUp();
45            notifyStarted();
46          } catch (Throwable t) {
47            notifyFailed(t);
48            throw Throwables.propagate(t);
49          }
50        }
51      });
52    }
53
54    @Override
55    protected final void doStop() {
56      executor().execute(new Runnable() {
57        public void run() {
58          try {
59            shutDown();
60            notifyStopped();
61          } catch (Throwable t) {
62            notifyFailed(t);
63            throw Throwables.propagate(t);
64          }
65        }
66      });
67    }
68  };
69
70  /** Constructor for use by subclasses. */
71  protected AbstractIdleService() {}
72
73  /** Start the service. */
74  protected abstract void startUp() throws Exception;
75
76  /** Stop the service. */
77  protected abstract void shutDown() throws Exception;
78
79  /**
80   * Returns the {@link Executor} that will be used to run this service.
81   * Subclasses may override this method to use a custom {@link Executor}, which
82   * may configure its worker thread with a specific name, thread group or
83   * priority. The returned executor's {@link Executor#execute(Runnable)
84   * execute()} method is called when this service is started and stopped,
85   * and should return promptly.
86   */
87  protected Executor executor() {
88    final State state = state();
89    return new Executor() {
90
91      public void execute(Runnable command) {
92        MoreExecutors.newThread(serviceName() + " " + state, command).start();
93      }
94    };
95  }
96
97  @Override
98  public String toString() {
99    return serviceName() + " [" + state() + "]";
100  }
101
102  // We override instead of using ForwardingService so that these can be final.
103
104  public final ListenableFuture<State> start() {
105    return delegate.start();
106  }
107
108  public final State startAndWait() {
109    return delegate.startAndWait();
110  }
111
112  public final boolean isRunning() {
113    return delegate.isRunning();
114  }
115
116  public final State state() {
117    return delegate.state();
118  }
119
120  public final ListenableFuture<State> stop() {
121    return delegate.stop();
122  }
123
124  public final State stopAndWait() {
125    return delegate.stopAndWait();
126  }
127
128  /**
129   * @since 13.0
130   */
131  public final void addListener(Listener listener, Executor executor) {
132    delegate.addListener(listener, executor);
133  }
134
135  /**
136   * @since 14.0
137   */
138  public final Throwable failureCause() {
139    return delegate.failureCause();
140  }
141
142  /**
143   * Returns the name of this service. {@link AbstractIdleService} may include the name in debugging
144   * output.
145   *
146   * @since 14.0
147   */
148  protected String serviceName() {
149    return getClass().getSimpleName();
150  }
151}
152