安卓联系人源码 之AsyncTaskExecutors分析

/*
* Copyright (C) 2011 The Android Open Source Project
*
* 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.android.contacts.util;

import android.os.AsyncTask;
import android.os.Looper;

import com.google.common.base.Preconditions;

import java.util.concurrent.Executor;

/**
* Factory methods for creating AsyncTaskExecutors.
* <p>
* All of the factory methods on this class check first to see if you have set a static
* {@link AsyncTaskExecutorFactory} set through the
* {@link #setFactoryForTest(AsyncTaskExecutorFactory)} method, and if so delegate to that instead,
* which is one way of injecting dependencies for testing classes whose construction cannot be
* controlled such as {@link android.app.Activity}.
*/
public final class AsyncTaskExecutors {
/**
* A single instance of the {@link AsyncTaskExecutorFactory}, to which we delegate if it is
* non-null, for injecting when testing.
*/
private static AsyncTaskExecutorFactory mInjectedAsyncTaskExecutorFactory = null;

/**
* Creates an AsyncTaskExecutor that submits tasks to run with
* {@link AsyncTask#SERIAL_EXECUTOR}.
*/
public static AsyncTaskExecutor createAsyncTaskExecutor() {
synchronized (AsyncTaskExecutors.class) {
if (mInjectedAsyncTaskExecutorFactory != null) {
return mInjectedAsyncTaskExecutorFactory.createAsyncTaskExeuctor();
}
//内部是AsynTask内部实现的SerialExecutor  SerialExecutor内部实现是封装了一个ArrayDeque，执行时从栈顶开始执行
return new SimpleAsyncTaskExecutor(AsyncTask.SERIAL_EXECUTOR);
}
}

/**
* Creates an AsyncTaskExecutor that submits tasks to run with
* {@link AsyncTask#THREAD_POOL_EXECUTOR}.
*/
public static AsyncTaskExecutor createThreadPoolExecutor() {
synchronized (AsyncTaskExecutors.class) {
if (mInjectedAsyncTaskExecutorFactory != null) {
return mInjectedAsyncTaskExecutorFactory.createAsyncTaskExeuctor();
}
//内部是一个标准的线程池 public static final Executor THREAD_POOL_EXECUTOR
//= new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
//      TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);
return new SimpleAsyncTaskExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
}

/** Interface for creating AsyncTaskExecutor objects. */
public interface AsyncTaskExecutorFactory {
AsyncTaskExecutor createAsyncTaskExeuctor();
}

public static void setFactoryForTest(AsyncTaskExecutorFactory factory) {
synchronized (AsyncTaskExecutors.class) {
mInjectedAsyncTaskExecutorFactory = factory;
}
}

public static void checkCalledFromUiThread() {
//检查AsynTask是否在主线程调用，asyntask必须在主线程调用
//此处用到了谷歌的一个包，如果不想导入额外的包的话可换一种方式实现
//if(Looper.myLooper() == Looper.getMainLooper()) {
//throw new RuntimeException("Please don\'t call in the UI thread");
// }
Preconditions.checkState(Thread.currentThread() == Looper.getMainLooper().getThread(),
"submit method must be called from ui thread, was: " + Thread.currentThread());
}

private static class SimpleAsyncTaskExecutor implements AsyncTaskExecutor {
private final Executor mExecutor;
//对线程池进行二次封装，执行任务时判断是否为主线程
public SimpleAsyncTaskExecutor(Executor executor) {
mExecutor = executor;
}

@Override
public <T> AsyncTask<T, ?, ?> submit(Object identifier, AsyncTask<T, ?, ?> task,
T... params) {
checkCalledFromUiThread();
return task.executeOnExecutor(mExecutor, params);
}
}
}