| /* |
| * 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.common.base.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 static final Runnable DO_NOTHING = |
| new Runnable() { |
| @Override |
| public void run() {} |
| }; |
| |
| private final ExecutorService executor; |
| |
| private volatile State state; |
| |
| public AsyncService(ExecutorService executor) { |
| this.executor = executor; |
| } |
| |
| @Override |
| public final synchronized 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>(DO_NOTHING, State.STARTED); |
| } |
| |
| return executor.submit( |
| new Callable<State>() { |
| @Override |
| 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(); |
| |
| @Override |
| public final synchronized 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>(DO_NOTHING, State.STOPPED); |
| } |
| |
| return executor.submit( |
| new Callable<State>() { |
| @Override |
| 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(); |
| |
| @Override |
| public final State state() { |
| return state; |
| } |
| } |