Java实现限定时间CountDownLatch并行场景

业务场景：

一个用户数据接口，要求在20ms内返回数据，它的调用逻辑复杂，关联接口多，需要从3个接口汇总数据，这些汇总接口最小耗时也需要16ms,全部汇总接口最优状态耗时需要16ms*3=48ms

解决方案：

使用并行调用接口，通过多线程同时获取结果集，最后进行结果整合。在这种场景下，使用concurrent包的CountDownLatch完成相关操作。CountDownLatch本质上是一个计数器，把它初始化为与执行任务相同的数量，当一个任务执行完时，就将计数器的值减1，直到计算器达到0时，表示完成了所有任务，在await上等待线程就继续执行。

为上述业务场景封装的工具类，传入两个参数：一个参数是计算的task数量，另外一个参数是整个大任务超时的毫秒数。

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									import java.util.concurrent.ArrayBlockingQueue;

									import java.util.concurrent.CountDownLatch;

									import java.util.concurrent.ThreadPoolExecutor;

									import java.util.concurrent.TimeUnit;

									public class ParallelCollector {

									    private Long timeout;

									    private CountDownLatch countDownLatch;

									    ThreadPoolExecutor executor = new ThreadPoolExecutor(100, 200, 1, TimeUnit.HOURS, new ArrayBlockingQueue<>(100));

									    public ParallelCollector(int taskSize, Long timeOutMill) {

									        countDownLatch = new CountDownLatch(taskSize);

									        timeout = timeOutMill;

									    }

									    public void submitTask(Runnable runnable) {

									        executor.execute(() -> {

									            runnable.run();

									            countDownLatch.countDown();

									        });

									    }

									    public void await() {

									        try {

									            this.countDownLatch.await(timeout, TimeUnit.MILLISECONDS);

									        } catch (InterruptedException e) {

									            e.printStackTrace();

									        }

									    }

									    public void destroy() {

									        this.executor.shutdown();

									    }

									}

当任务运行时间超过了任务的时间上限，就被直接停止，这就是await()的功能。

interface是一个模拟远程服务的超时的测试类，程序运行后，会输出执行结果到map集合。

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									public class InterfaceMock {

									    private  volatile  int num=1;

									   public String slowMethod1() {

									        try {

									            Thread.sleep(2000);

									        } catch (InterruptedException e) {

									            e.printStackTrace();

									        }

									        return String.valueOf(num+1);

									    };

									   public String slowMethod2() {

									        return String.valueOf(num+1);

									    };

									   public String slowMethod3() {

									        return String.valueOf(num+1);

									    };

									}

并行执行获取结果测试类

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									@SpringBootTest

									class ThreadPoolApplicationTests {

									    @Test

									    void testTask() {

									        InterfaceMock interfaceMock = new InterfaceMock();

									        ParallelCollector collector = new ParallelCollector(3, 20L);

									        ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();

									        collector.submitTask(()->map.put("method1",interfaceMock.slowMethod1()));

									        collector.submitTask(()->map.put("method2",interfaceMock.slowMethod2()));

									        collector.submitTask(()->map.put("method3",interfaceMock.slowMethod3()));

									        collector.await();

									        System.out.println(map.toString());

									        collector.destroy();

									    }

									}