| /** |
| * Copyright (C) 2010 Google Inc. |
| * |
| * Licensed 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 com.google.inject.service; |
| |
| import com.google.inject.internal.util.Preconditions; |
| import java.util.concurrent.Callable; |
| import java.util.concurrent.ExecutorService; |
| import java.util.concurrent.Future; |
| import java.util.concurrent.FutureTask; |
| |
| /** |
| * An asynchronous implementation of {@link com.google.inject.service.Service} |
| * that provides convenience callbacks to create your own services. |
| * |
| * @author dhanji@gmail.com (Dhanji R. Prasanna) |
| */ |
| public abstract class AsyncService implements Service { |
| private final ExecutorService executor; |
| |
| /** |
| * A runnable that does nothing. |
| */ |
| private static final Runnable NOOP = new Runnable() { |
| public void run() { } |
| }; |
| |
| private volatile State state; |
| |
| public AsyncService(ExecutorService executor) { |
| this.executor = executor; |
| } |
| |
| public synchronized final Future<State> start() { |
| Preconditions.checkState(state != State.STOPPED, |
| "Cannot restart a service that has been stopped"); |
| |
| // Starts are idempotent. |
| if (state == State.STARTED) { |
| return new FutureTask<State>(NOOP, State.STARTED); |
| } |
| |
| return executor.submit(new Callable<State>() { |
| public State call() { |
| onStart(); |
| return state = State.STARTED; |
| } |
| }); |
| } |
| |
| /** |
| * Called back when this service must do its start work. Typically occurs |
| * in a background thread. The result of this method is returned to the |
| * original caller of {@link Service#start()} and can thus be used to |
| * return a status message after start completes (or fails as the case |
| * may be). |
| */ |
| protected abstract void onStart(); |
| |
| public synchronized final Future<State> stop() { |
| Preconditions.checkState(state != null, "Must start this service before you stop it!"); |
| |
| // Likewise, stops are idempotent. |
| if (state == State.STOPPED) { |
| return new FutureTask<State>(NOOP, State.STOPPED); |
| } |
| |
| return executor.submit(new Callable<State>() { |
| public State call() { |
| onStop(); |
| return state = State.STOPPED; |
| } |
| }); |
| } |
| |
| /** |
| * Called back when this service must shutdown. Typically occurs |
| * in a background thread. The result of this method is returned to the |
| * original caller of {@link Service#stop()} and can thus be used to |
| * return a status message after stop completes (or fails as the case |
| * may be). |
| */ |
| protected abstract void onStop(); |
| |
| public final State state() { |
| return state; |
| } |
| } |