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Java中经常存在以下的需求，启动多个相同或者不同的线程，主线程需要等待所有的线程执行完才继续往下执行
要实现上面的需求，基本的思路： 创建一个计数器， 来记录线程的执行
有两种实现方法
方法1：
使用锁和计数器：需要有一个对象锁，作用一：保证这个计数器的线程安全，作用二：阻塞主线程，等待所有线程执行完再来唤醒主线程继续执行
方法2：
使用Java线程包中的CountDownLatch：不需要加锁， 不需要wait notify这么复杂
方法1：
package com.yaya.thread.threadCount.count;import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class TestCount {int count = 0;int total = 0;Object object = new Object();void testCount() {total = 10;ExecutorService pool = Executors.newFixedThreadPool(5);for (int i = 0; i < 10; i++) {final int j = i;Runnable runnable = new Runnable() {@Overridepublic void run() {// TODO Auto-generated method stubtry {System.out.println("runnalbe:" + j);Thread.sleep(2000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();} finally {synchronized (object) {count++;if (count == total) {object.notify();}}}}};pool.execute(runnable);}synchronized (object) {if (count != total) {try {object.wait();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}System.out.println("end");pool.shutdown();}public static void main(String[] args) {TestCount testCount = new TestCount();testCount.testCount();}}
方法2： CountDownLatch
package com.yaya.thread.threadCount.countDownLatch;import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;import com.yaya.thread.future.ThreadPoolUtil;public class TestCountDownLatch {static CountDownLatch count = null;public void testRunnalbe(){List<String> list = new ArrayList<String>();for (int i = 1; i <= 10; i++) {list.add("list" + i);}count = new CountDownLatch(list.size());List<Runnable> runnables = new ArrayList<Runnable>();for (int i = 0; i < list.size(); i++) {final String listName = list.get(i);Runnable runnable = new TestRunnable1(listName, count);runnables.add(runnable);}try {ThreadPoolUtil.exeRunnableList(runnables);} catch (Exception e) {System.err.println(e.getMessage());}try {count.await();System.out.println("end");ThreadPoolUtil.shutDown(true);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}public void testDifferentRunnalbes(){List<String> list = new ArrayList<String>();for (int i = 1; i <= 10; i++) {list.add("list" + i);}count = new CountDownLatch(list.size()*2);List<Runnable> runnables = new ArrayList<Runnable>();for (int i = 0; i < list.size(); i++) {final String listName = list.get(i);Runnable runnable = new TestRunnable1(listName, count);runnables.add(runnable);}for (int i = 0; i < list.size(); i++) {final String listName = list.get(i);Runnable runnable = new TestRunnable2(listName, count);runnables.add(runnable);}try {ThreadPoolUtil.exeRunnableList(runnables);} catch (Exception e) {System.err.println(e.getMessage());}try {count.await();System.out.println("end");ThreadPoolUtil.shutDown(true);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}public static void main(String[] args) {TestCountDownLatch testCountDownLatch = new TestCountDownLatch();testCountDownLatch.testDifferentRunnalbes();}}
package com.yaya.thread.threadCount.countDownLatch;import java.util.concurrent.CountDownLatch;public class TestRunnable2 implements Runnable {String appid;CountDownLatch count;public TestRunnable2(String appid, CountDownLatch count) {super();this.appid = appid;this.count = count;}@Overridepublic void run() {System.out.println("task" + this.appid + "开始");try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("task" + this.appid + "睡了3s");count.countDown();}}
package com.yaya.thread.future;import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;public class ThreadPoolUtil {// 线程池private static ThreadPoolExecutor threadPool;// 线程池核心线程数private static final int CORE_POOL_SIZE = 5;// 线程池最大线程数private static final int MAX_POOL_SIZE = 10;// 额外线程空状态生存时间private static final int KEEP_ALIVE_TIME = 10000;private static final int CANCEL_TASK_TIME = 20;private ThreadPoolUtil() {}static {threadPool = new ThreadPoolExecutor(CORE_POOL_SIZE, MAX_POOL_SIZE, KEEP_ALIVE_TIME, TimeUnit.SECONDS,new LinkedBlockingQueue<>(30), new ThreadFactory() {private final AtomicInteger integer = new AtomicInteger();@Overridepublic Thread newThread(Runnable r) {return new Thread(r, "mock thread:" + integer.getAndIncrement());}});}/*** 从线程池中抽取线程，执行指定的Runnable对象* * @param runnable*/public static void execute(Runnable runnable) {threadPool.execute(runnable);}/*** 批量执行 Runnable任务* * @param runnableList*/public static void exeRunnableList(List<Runnable> runnableList) {for (Runnable runnable : runnableList) {threadPool.execute(runnable);}}/*** 从线程池中抽取线程，执行指定的Callable对象* * @param callable* @return 返回执行完毕后的预期结果*/public static Future exeCallable(Callable<String> callable) {return threadPool.submit(callable);}/*** 批量执行 Callable任务* * @param callableList* callable的实例列表* @return 返回指定的预期执行结果*/public static List<Future<String>> exeCallableList(List<Callable<String>> callableList) {List<Future<String>> futures = null;try {for (Callable<String> task : callableList) {threadPool.submit(task);}futures = threadPool.invokeAll(callableList);} catch (InterruptedException e) {e.printStackTrace();}return futures;}/*** 批量执行 Callable任务， 但不等待执行完* * @param callableList* callable的实例列表* @return 返回指定的预期执行结果*/public static void exeCallableListNoReturn(List<Callable<String>> callableList) {for (Callable<String> task : callableList) {threadPool.submit(task);}}/*** 中断任务的执行* * @param isForceClose* true:强制中断 false:等待任务执行完毕后，关闭线程池*/public static void shutDown(boolean isForceClose) {if (isForceClose) {threadPool.shutdownNow();} else {threadPool.shutdown();}}/*** 若超出CANCEL_TASK_TIME的时间，没有得到执行结果，则尝试中断线程* * @param future* @return 中断成功，则返回true 否则返回false*/public static boolean attemptCancelTask(Future future) {boolean cancel = false;try {future.get(CANCEL_TASK_TIME, TimeUnit.MINUTES);cancel = true;} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();} catch (TimeoutException e) {cancel = future.cancel(true);e.printStackTrace();}return cancel;}}
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