CountDownLatch 实例代码：
package com.mmall.concurrency.example.aqs; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; @Slf4j public class CountDownLatchExample1 { private final static int threadCount = 200; public static void main(String[] args) throws Exception { ExecutorService exec = Executors.newCachedThreadPool(); final CountDownLatch countDownLatch = new CountDownLatch(threadCount); for (int i = 0; i < threadCount; i++) { final int threadNum = i; exec.execute(() -> { try { test(threadNum); } catch (Exception e) { log.error("exception", e); } finally { countDownLatch.countDown(); } }); } countDownLatch.await(); log.info("finish"); exec.shutdown(); } private static void test(int threadNum) throws Exception { Thread.sleep(100); log.info("{}", threadNum); Thread.sleep(100); } } semaphore : 控制并发访问的线程个数
package com.mmall.concurrency.example.aqs; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; import java.util.concurrent.TimeUnit; @Slf4j public class SemaphoreExample3 { private final static int threadCount = 20; public static void main(String[] args) throws Exception { ExecutorService exec = Executors.newCachedThreadPool(); final Semaphore semaphore = new Semaphore(3); for (int i = 0; i < threadCount; i++) { final int threadNum = i; exec.execute(() -> { try { if (semaphore.tryAcquire()) { // 尝试获取一个许可 test(threadNum); semaphore.release(); // 释放一个许可 } } catch (Exception e) { log.error("exception", e); } }); } exec.shutdown(); } private static void test(int threadNum) throws Exception { log.info("{}", threadNum); Thread.sleep(1000); } } cyclicBarrier: 使用场景和countDownLatch的使用场景很类似，但是可以循环的使用
实现了多个线程之间的相互等待，知道所有的线程都执行完成之后，才进行下一步的操作
package com.mmall.concurrency.example.aqs; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CyclicBarrier; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; @Slf4j public class CyclicBarrierExample2 { private static CyclicBarrier barrier = new CyclicBarrier(5); public static void main(String[] args) throws Exception { ExecutorService executor = Executors.newCachedThreadPool(); for (int i = 0; i < 10; i++) { final int threadNum = i; Thread.sleep(1000); executor.execute(() -> { try { race(threadNum); } catch (Exception e) { log.error("exception", e); } }); } executor.shutdown(); } private static void race(int threadNum) throws Exception { Thread.sleep(1000); log.info("{} is ready", threadNum); try { barrier.await(2000, TimeUnit.MILLISECONDS); } catch (Exception e) { log.warn("BarrierException", e); } log.info("{} continue", threadNum); } } 设置达到资源屏障时优先执行的方法：
package com.mmall.concurrency.example.aqs; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CyclicBarrier; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; @Slf4j public class CyclicBarrierExample3 { private static CyclicBarrier barrier = new CyclicBarrier(5, () -> { log.info("callback is running"); }); public static void main(String[] args) throws Exception { ExecutorService executor = Executors.newCachedThreadPool(); for (int i = 0; i < 10; i++) { final int threadNum = i; Thread.sleep(1000); executor.execute(() -> { try { race(threadNum); } catch (Exception e) { log.error("exception", e); } }); } executor.shutdown(); } private static void race(int threadNum) throws Exception { Thread.sleep(1000); log.info("{} is ready", threadNum); barrier.await(); log.info("{} continue", threadNum); } } 来源：博客园
作者：青紫天涯
链接：https://www.cnblogs.com/wcgstudy/p/11509780.html