线程协作测试

题目来自今年某公司一次笔试试题。

大致题目要求为：

一个线程A及一组线程B，令线程A触发B线程执行后进行等待，待线程B全部执行完毕后，A继续执行，求方案。

最简单的用wait/notify：

/*** 线程A*/import java.util.ArrayList;import java.util.Iterator;public class ThreadA implements Runnable {    private ArrayList<Runnable> threadbs;    public void run() {System.out.println("ThreadA start");threadbs = new ArrayList<Runnable>();for(int i = 0;i<10;i++) {    threadbs.add(new ThreadB(this));}Iterator<Runnable> iterator = threadbs.iterator();while(iterator.hasNext()) {    motiveThreadB(iterator.next());}synchronized(this) {        try {            System.out.println("ThreadA starting to wait");            wait();        } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }}System.out.println("ThreadB all seem to be ended");    }    public void motiveThreadB(Runnable r) {new Thread(r).start();    }}

/*** 线程B*/import java.util.concurrent.atomic.AtomicInteger;public class ThreadB implements Runnable {    private ThreadA ta;    private static int id = 0;    private int seq ;    private static AtomicInteger counter = new AtomicInteger(0);    public ThreadB(ThreadA t) {this.ta = t;seq = id++;    }    @Override    public void run() {System.out.println("ThreadB "+seq+"started");counter.addAndGet(1);try {    Thread.sleep(10);} catch (InterruptedException e) {    // TODO Auto-generated catch block    e.printStackTrace();}System.out.println("ThreadB "+seq+"ended");if(counter.decrementAndGet()==0) {    synchronized(ta) {    ta.notify();    }}    }}

/***驱动测试代码*/import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class TestDriver {    /**     * @param args     */    public static void main(String[] args) {// TODO Auto-generated method stubExecutorService exec = Executors.newCachedThreadPool();exec.execute(new ThreadA());exec.shutdown();    }}

方案二：使用容量为1的阻塞队列，将wait和notify操作改为对队列的阻塞操作。

/** 线程A*/public class ThreadA implements Runnable{    LinkedBlockingQueue<String> bq = new LinkedBlockingQueue<String>(1);    public void run() {ArrayList<Runnable> threadbs = new ArrayList<Runnable>();System.out.println("init bq");for(int i = 0;i<10;i++) {    threadbs.add(new ThreadB(this));}Iterator<Runnable> iterator = threadbs.iterator();while(iterator.hasNext()) {   new Thread(iterator.next()).start();}System.out.println("try to blocked insert element");try {    bq.take();} catch (InterruptedException e) {    e.printStackTrace();}System.out.println("Added element successfully");System.out.println("ThreadB all seem to be ended");    }}

/*** 线程B的关键代码*/public void run() {System.out.println("Thread+"+seq+"started");counter.addAndGet(1);try {    Thread.sleep(10);} catch (InterruptedException e) {    e.printStackTrace();}if(counter.decrementAndGet()==0) {    System.out.println("Thread+"+seq+"removeded element"+ta.bq.add("c"));}System.out.println("Thread+"+seq+"ended");    }