前言
做Android的这两年时间,通过研究Android源码,也会Java并发处理多线程有了自己的一些理解。
那么问题来了,如何实现一个串行的线程池呢?
思路
何为串行线程池呢?
也就是说,我们的Runnable对象应该有个排队的机制,它们顺序从队列尾部进入,并且从队列头部选择Runnable进行执行。
既然我们有了思路,那我们就考虑一下所需要的数据结构?
既然是从队列尾部插入Runnable对象,从队列头部执行Runnable对象,我们自然需要一个队列。Java的SDK已经给我们提供了很好的队列数据结构,例如双端队列:ArrayDeque<Runnable>。
- 因为涉及到线程的执行,那我们首先就需要有一个合适的线程池,使用ThreadPoolExecutor类即可构造。
- 既然是串行执行,那如何保持串行机制呢?我们可以通过try和finally机制,我们将传入的Runnable对象重新封装成一个新的Runnable对象,在新的Runnable的run方法的try块中执行Runnable的run方法,在finally中调用执行队列头部Runnable对象出队列,并放入线程池执行的方法。
示例代码
import java.util.ArrayDeque;import java.util.concurrent.BlockingQueue;import java.util.concurrent.LinkedBlockingDeque;import java.util.concurrent.ThreadFactory;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicInteger;/** * Created by wzy on 16-1-5. */public class SerialExecutor { private Runnable mActive; private ArrayDeque<Runnable> mArrayDeque = new ArrayDeque<>(); private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors(); private static final int CORE_POOL_SIZE = CPU_COUNT + 1; private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1; private static final int KEEP_ALIVE = 1; private static final BlockingQueue<Runnable> sPoolWorkQueue = new LinkedBlockingDeque<>(128); private static final ThreadFactory sThreadFactory = new ThreadFactory() { private final AtomicInteger mCount = new AtomicInteger(1); @Override public Thread newThread(Runnable r) { return new Thread(r, "Serial thread #" + mCount.getAndIncrement()); } }; private static final ThreadPoolExecutor THREAD_EXECUTOR = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory); public synchronized void execute(final Runnable r) { mArrayDeque.offer(new Runnable() { @Override public void run() { try { r.run(); } finally { scheduleNext(); } } }); // 第一次入队列时mActivie为空,因此需要手动调用scheduleNext方法 if (mActive == null) { scheduleNext(); } } private void scheduleNext() { if ((mActive = mArrayDeque.poll()) != null) { THREAD_EXECUTOR.execute(mActive); } } public static void main(String[] args) { SerialExecutor serialExecutor = new SerialExecutor(); for (int i = 0; i < 10; i ++) { final int j = i; serialExecutor.execute(new Runnable() { @Override public void run() { System.out.println("The num is :" + (j + 1)); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } }); } }}
执行结果如下:
The num is :1
The num is :2
The num is :3
The num is :4
The num is :5
The num is :6
The num is :7
The num is :8
The num is :9
The num is :10
总结
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