ReentrantLock、StampedLock、ReentrantReadWriteLock、Condition 锁分为Synchronized和锁Lock。ReentrantLock与锁ReentrantLock(可重入锁)与Synchronized(同步锁)的区别：可重入性：区别不大，都是通过计数器，当计数器下降为0时，锁释放。锁的实现：Synchronized依赖JVM，ReentrantLock基于JDK实现。(类似Synchronized是操作系统实现，ReentrantLock是敲代码实现),ReentrantLock可通过看源码明白实现，Synchronized依赖JVM就看不到实现原理。性能的区别：优化之前Synchronized比ReentrantLock性能差很多，优化后Synchronized引入偏向锁、轻量级锁也就是自旋锁后，2者性能差不多了。差不多时，官方推荐Synchronized。功能的区别：Synchronized的使用方便简洁，隐式获取锁释放锁，ReentrantLock需要手动获取锁，释放锁，如果忘记容易出现死锁，所以最好再finally中释放锁。锁的颗粒度和灵活度很明显ReentrantLock优于Synchronized。ReentrantLock独有的功能：ReentrantLock可指定公平锁、非公平锁，而Synchronized只能时非公平锁。公平锁：先等待的先获取锁，反之亦然。提供了一个Condition类，可以分组唤醒需要唤醒的线程，Synchronized要么随机唤醒，要么全部唤醒。提供能够中断等待锁的线程的机制，lock.lockInterruptibly()，lockInterruptibly是一种自旋锁，通过循环来调用CAS来加锁，性能比较好，就是因为不会进入内核阻塞状态。使用场景：必须实现上面3个功能时，就必须用了。代码示例一ReentrantLock实现累加，注意与synchronized的不用用法package com.yanxizhu.demo.concurrency.lock; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @description: ReentrantLock锁实现计数，注意使用synchroized怎么实现的 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 23:09 * @version: 1.0 */ @Slf4j public class ReentrantLockDemo { //定义锁 private static Lock lock = new ReentrantLock(); //定义锁用户数 private static final int totalThread = 5000; //定义并发线程数 private static final int concurrentThread = 200; //定义总和 private static int count = 0; public static void main(String[] args) throws Exception{ //定义线程池 ExecutorService executorService = Executors.newCachedThreadPool(); //定义信号量 final Semaphore semaphore = new Semaphore(concurrentThread); //定义闭锁 final CountDownLatch countDownLatch = new CountDownLatch(totalThread); for (int i = 0; i < totalThread; i++) { executorService.execute(() -> { try { semaphore.acquire(); sum(); semaphore.release(); } catch (InterruptedException e) { log.error("错误信息:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("最后累加结果Count={}", count); } //通过ReentrantLock锁实现 public static void sum() { lock.lock(); count++; lock.unlock(); } //累加求和(synchronized锁实现) // public synchronized static void sum() { // count ++; // } }输出结果:23:21:08.549 [main] INFO com.yanxizhu.demo.concurrency.lock.ReentrantLockDemo - 最后累加结果Count=5000源码查看public ReentrantLock() { sync = new NonfairSync(); }默认传入的是不公平的锁。 public ReentrantLock(boolean fair) { sync = fair ? new FairSync() : new NonfairSync(); }可以传入ture或false决定是否是公平锁。需要注意的方法tryLok： public boolean tryLock() { return sync.nonfairTryAcquire(1); }本质是仅在调用的时候，锁定未被另一个线程持有的情况下，才锁定。参数同样可以传入超时时间和单位，保持线程时间多久可以锁定。提供了丰富的方法，可以参考官方文档，ReentrantReadWriteLock没有任何读写锁的时候，才可以取得写入锁。可实现悲观读取。读多写少时，可能会导致写进入饥饿。注意是悲观锁，当有读时，写可能一直执行不了，有写的时候，不能读。代码示例package com.yanxizhu.demo.concurrency.lock; import java.util.Map; import java.util.Set; import java.util.TreeMap; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantReadWriteLock; /** * @description: ReentrantReadWriteLock 读锁、写锁的使用 * 注意： ReentrantReadWriteLock时悲观锁，读的时候不能写，写的时候不能读，互斥的 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 23:40 * @version: 1.0 */ public class ReentrantReadWriteLockDemo { //定义读写锁 private static final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(); //获取读锁 private static final Lock readLock = lock.readLock(); //获取写锁 private static final Lock writeLock = lock.writeLock(); private static Map<String, Data> map = new TreeMap<>(); public class Data{ } //读map中的数据 public Data getValue(String key) { readLock.lock(); try{ return map.get(key); }catch (Exception e) { }finally { readLock.unlock(); } return null; } //读取map中所有的key public Set<String> getKeys() { readLock.lock(); try{ return map.keySet(); }catch (Exception e) { }finally { readLock.unlock(); } return null; } //向map中写入数据 public void writeDate(String key, Data value) { writeLock.lock(); try{ map.put(key, value); }catch (Exception e){ }finally { writeLock.unlock(); } } }StampedLockStampedLock控制锁，有3种模式。写、读、是由锁和版本控制，就是这里的。读分为悲观读和乐观读。官方代码示例package com.yanxizhu.demo.concurrency.lock; import java.util.concurrent.locks.StampedLock; public class StampedLockDemo { class Point { private double x, y; private final StampedLock sl = new StampedLock(); void move(double deltaX, double deltaY) { // an exclusively locked method long stamp = sl.writeLock(); try { x += deltaX; y += deltaY; } finally { sl.unlockWrite(stamp); } } //下面看看乐观读锁案例 double distanceFromOrigin() { // A read-only method long stamp = sl.tryOptimisticRead(); //获得一个乐观读锁 double currentX = x, currentY = y; //将两个字段读入本地局部变量 if (!sl.validate(stamp)) { //检查发出乐观读锁后同时是否有其他写锁发生？ stamp = sl.readLock(); //如果没有，我们再次获得一个读悲观锁 try { currentX = x; // 将两个字段读入本地局部变量 currentY = y; // 将两个字段读入本地局部变量 } finally { sl.unlockRead(stamp); } } return Math.sqrt(currentX * currentX + currentY * currentY); } //下面是悲观读锁案例 void moveIfAtOrigin(double newX, double newY) { // upgrade // Could instead start with optimistic, not read mode long stamp = sl.readLock(); try { while (x == 0.0 && y == 0.0) { //循环，检查当前状态是否符合 long ws = sl.tryConvertToWriteLock(stamp); //将读锁转为写锁 if (ws != 0L) { //这是确认转为写锁是否成功 stamp = ws; //如果成功 替换票据 x = newX; //进行状态改变 y = newY; //进行状态改变 break; } else { //如果不能成功转换为写锁 sl.unlockRead(stamp); //我们显式释放读锁 stamp = sl.writeLock(); //显式直接进行写锁 然后再通过循环再试 } } } finally { sl.unlock(stamp); //释放读锁或写锁 } } } }示例代码二累加求和package com.yanxizhu.demo.concurrency.lock; import lombok.extern.slf4j.Slf4j; import javax.annotation.concurrent.ThreadSafe; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; import java.util.concurrent.locks.StampedLock; @Slf4j @ThreadSafe public class StampedLockDemo2 { // 请求总数 public static int clientTotal = 5000; // 同时并发执行的线程数 public static int threadTotal = 200; public static int count = 0; private final static StampedLock lock = new StampedLock(); public static void main(String[] args) throws Exception { ExecutorService executorService = Executors.newCachedThreadPool(); final Semaphore semaphore = new Semaphore(threadTotal); final CountDownLatch countDownLatch = new CountDownLatch(clientTotal); for (int i = 0; i < clientTotal ; i++) { executorService.execute(() -> { try { semaphore.acquire(); add(); semaphore.release(); } catch (Exception e) { log.error("exception", e); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("count:{}", count); } private static void add() { //这里加锁，返回值 long stamp = lock.writeLock(); try { count++; } finally { //释放锁，带上加锁的返回值 lock.unlock(stamp); } } }输出结果：5000，线程安全，并发性好。Condition代码示例package com.yanxizhu.demo.concurrency.lock; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock; /** * ReentrantLock中另一个队列，Condition的使用 */ @Slf4j public class ConditionDemo { public static void main(String[] args) { ReentrantLock reentrantLock = new ReentrantLock(); Condition condition = reentrantLock.newCondition(); new Thread(() -> { try { reentrantLock.lock(); log.info("wait signal"); // 1 condition.await(); } catch (InterruptedException e) { e.printStackTrace(); } log.info("get signal"); // 4 reentrantLock.unlock(); }).start(); new Thread(() -> { reentrantLock.lock(); log.info("get lock"); // 2 try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } condition.signalAll(); log.info("send signal ~ "); // 3 reentrantLock.unlock(); }).start(); } }

J.U.C之AQS AQSJ.U.C之AQS，底层由线程队列实现。AbstractQueuedSynchronizer简称AQS，JUC的核心。使用Node实现FIFO队列，可以用于构建锁或者其他同步装置的基础框架。利用了一个int类型表示状态。使用方法是继承。子类通过继承并通过实现它的方法管理其状态{acquire和release}的方法操纵状态。可以同时实现排它锁和共享锁模式（独占、共享）。AQS主要同步组件CountDownLatchSemaphoreCyclicBarrierReentrantLockConditionFutureTask依次介绍1、CountDownLatch-闭锁可以完成类似阻塞的功能。一个线程或多个线程等待，直到其它线程完成。使用场景，程序执行需要某个条件执行完后，才执行。示例一package com.yanxizhu.demo.concurrency.aqs; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * @description: CountDownLatch,实现线程阻塞，等待执行完再执行程序打印 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 20:24 * @version: 1.0 */ @Slf4j @ThreadSafety public class CountDownLatchDemo { private static final int threadNum = 500; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); CountDownLatch countDownLatch = new CountDownLatch(threadNum); for (int i = 0; i <threadNum; i++) { final int num = i; executorService.execute(() -> { try{ pringNum(num); }catch (Exception e){ log.error("执行错误【{}】", e.getMessage()); }finally { countDownLatch.countDown(); } }); } countDownLatch.await(); executorService.shutdown(); log.info("finash .."); } public static void pringNum(int num) throws InterruptedException { Thread.sleep(100); log.info("num=【{}】", num); Thread.sleep(100); } }输出结果：。。。。。 20:36:34.598 [pool-1-thread-249] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【248】 20:36:34.608 [pool-1-thread-259] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【258】 20:36:34.597 [pool-1-thread-237] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【236】 20:36:34.597 [pool-1-thread-206] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【205】 20:36:34.608 [pool-1-thread-256] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【255】 20:36:34.608 [pool-1-thread-258] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【257】 20:36:34.597 [pool-1-thread-240] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【239】 20:36:34.597 [pool-1-thread-67] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【66】 20:36:34.608 [pool-1-thread-251] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【250】 20:36:34.608 [pool-1-thread-257] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【256】 20:36:34.608 [pool-1-thread-44] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【43】 20:36:34.598 [pool-1-thread-61] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【60】 20:36:34.598 [pool-1-thread-33] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【32】 20:36:34.597 [pool-1-thread-172] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【171】 20:36:34.608 [pool-1-thread-230] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【229】 20:36:34.608 [pool-1-thread-253] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【252】 20:36:34.598 [pool-1-thread-59] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【58】 20:36:34.598 [pool-1-thread-39] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【38】 20:36:34.608 [pool-1-thread-298] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【297】 20:36:34.596 [pool-1-thread-192] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【191】 20:36:34.597 [pool-1-thread-75] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【74】 20:36:34.608 [pool-1-thread-299] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【298】 20:36:34.597 [pool-1-thread-146] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【145】 20:36:34.608 [pool-1-thread-304] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【303】 20:36:34.598 [pool-1-thread-229] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【228】 20:36:34.597 [pool-1-thread-87] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【86】 20:36:34.597 [pool-1-thread-46] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - num=【45】 20:36:34.764 [main] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo - finash ..另一种用法，给定时间内未执行执行await方法。到时间等当前线程执行完成后就不执行了。示例一package com.yanxizhu.demo.concurrency.aqs; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; /** * @description: CountDownLatch,设置等待时间 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 20:24 * @version: 1.0 */ @Slf4j @ThreadSafety public class CountDownLatchDemo2 { private static final int threadNum = 500; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); CountDownLatch countDownLatch = new CountDownLatch(threadNum); for (int i = 0; i <threadNum; i++) { final int num = i; executorService.execute(() -> { try{ pringNum(num); }catch (Exception e){ log.error("执行错误【{}】", e.getMessage()); }finally { countDownLatch.countDown(); } }); } //设置了等待时间 countDownLatch.await(100, TimeUnit.MILLISECONDS); executorService.shutdown(); log.info("finash .."); } public static void pringNum(int num) throws InterruptedException { Thread.sleep(100); log.info("num=【{}】", num); } }输出结果20:39:27.285 [pool-1-thread-258] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【257】 20:39:27.284 [pool-1-thread-180] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【179】 20:39:27.287 [pool-1-thread-54] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【53】 20:39:27.283 [pool-1-thread-368] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【367】 20:39:27.285 [pool-1-thread-8] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【7】 20:39:27.301 [main] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - finash .. 20:39:27.286 [pool-1-thread-204] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【203】 20:39:27.301 [pool-1-thread-42] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【41】 20:39:27.305 [pool-1-thread-432] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【431】 20:39:27.285 [pool-1-thread-270] INFO com.yanxizhu.demo.concurrency.aqs.CountDownLatchDemo2 - num=【269】100毫秒后执行打印finash，之后的线程执行完后不再执行。2、Semaphore-信号量用于控制线程并发的个数。使用场景，提供仅限使用的资源。比如：有大量请求时，可用信号量控制数据库连接数，防止大量请求。示例一package com.yanxizhu.demo.concurrency.aqs; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.*; /** * @description: Semaphore-信号量，控制线程并发数 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 20:41 * @version: 1.0 */ @Slf4j @ThreadSafety public class SemaphoreDemo { private static final int threadNum = 20; private static final int currentThreadNum = 3; public static void main(String[] args) throws InterruptedException { //线程池 ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 Semaphore semaphore = new Semaphore(currentThreadNum); for (int i = 0; i <threadNum; i++) { final int num = i; executorService.execute(() -> { try{ //获取一个许可 semaphore.acquire(); pringNum(num); //释放一个许可 semaphore.release(); }catch (Exception e){ log.error("执行错误【{}】", e.getMessage()); } }); } executorService.shutdown(); } public static void pringNum(int num) throws InterruptedException { log.info("num=【{}】", num); Thread.sleep(1000); } }输出结果："C:\Program Files\jdk-11.0.10_windows-x64_bin\jdk-11.0.10\bin\java.exe" -Dvisualvm.id=83604261825100 "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.3.2\lib\idea_rt.jar=11416:C:\Program Files\JetBrains\IntelliJ IDEA 2020.3.2\bin" -Dfile.encoding=UTF-8 -classpath D:\Workspaces\ThreadConcurrency\demo-concurrency\target\classes;D:\Tools\repo\org\springframework\boot\spring-boot-starter-web\2.6.6\spring-boot-starter-web-2.6.6.jar;D:\Tools\repo\org\springframework\boot\spring-boot-starter\2.6.6\spring-boot-starter-2.6.6.jar;D:\Tools\repo\org\springframework\boot\spring-boot-starter-logging\2.6.6\spring-boot-starter-logging-2.6.6.jar;D:\Tools\repo\ch\qos\logback\logback-classic\1.2.11\logback-classic-1.2.11.jar;D:\Tools\repo\ch\qos\logback\logback-core\1.2.11\logback-core-1.2.11.jar;D:\Tools\repo\org\apache\logging\log4j\log4j-to-slf4j\2.17.2\log4j-to-slf4j-2.17.2.jar;D:\Tools\repo\org\apache\logging\log4j\log4j-api\2.17.2\log4j-api-2.17.2.jar;D:\Tools\repo\org\slf4j\jul-to-slf4j\1.7.36\jul-to-slf4j-1.7.36.jar;D:\Tools\repo\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;D:\Tools\repo\org\yaml\snakeyaml\1.29\snakeyaml-1.29.jar;D:\Tools\repo\org\springframework\boot\spring-boot-starter-json\2.6.6\spring-boot-starter-json-2.6.6.jar;D:\Tools\repo\com\fasterxml\jackson\core\jackson-databind\2.13.2.2\jackson-databind-2.13.2.2.jar;D:\Tools\repo\com\fasterxml\jackson\core\jackson-annotations\2.13.2\jackson-annotations-2.13.2.jar;D:\Tools\repo\com\fasterxml\jackson\core\jackson-core\2.13.2\jackson-core-2.13.2.jar;D:\Tools\repo\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.13.2\jackson-datatype-jdk8-2.13.2.jar;D:\Tools\repo\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.13.2\jackson-datatype-jsr310-2.13.2.jar;D:\Tools\repo\com\fasterxml\jackson\module\jackson-module-parameter-names\2.13.2\jackson-module-parameter-names-2.13.2.jar;D:\Tools\repo\org\springframework\boot\spring-boot-starter-tomcat\2.6.6\spring-boot-starter-tomcat-2.6.6.jar;D:\Tools\repo\org\apache\tomcat\embed\tomcat-embed-core\9.0.60\tomcat-embed-core-9.0.60.jar;D:\Tools\repo\org\apache\tomcat\embed\tomcat-embed-el\9.0.60\tomcat-embed-el-9.0.60.jar;D:\Tools\repo\org\apache\tomcat\embed\tomcat-embed-websocket\9.0.60\tomcat-embed-websocket-9.0.60.jar;D:\Tools\repo\org\springframework\spring-web\5.3.18\spring-web-5.3.18.jar;D:\Tools\repo\org\springframework\spring-beans\5.3.18\spring-beans-5.3.18.jar;D:\Tools\repo\org\springframework\spring-webmvc\5.3.18\spring-webmvc-5.3.18.jar;D:\Tools\repo\org\springframework\spring-aop\5.3.18\spring-aop-5.3.18.jar;D:\Tools\repo\org\springframework\spring-context\5.3.18\spring-context-5.3.18.jar;D:\Tools\repo\org\springframework\spring-expression\5.3.18\spring-expression-5.3.18.jar;D:\Tools\repo\org\springframework\boot\spring-boot-devtools\2.6.6\spring-boot-devtools-2.6.6.jar;D:\Tools\repo\org\springframework\boot\spring-boot\2.6.6\spring-boot-2.6.6.jar;D:\Tools\repo\org\springframework\boot\spring-boot-autoconfigure\2.6.6\spring-boot-autoconfigure-2.6.6.jar;D:\Tools\repo\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;D:\Tools\repo\org\slf4j\slf4j-api\1.7.36\slf4j-api-1.7.36.jar;D:\Tools\repo\org\springframework\spring-core\5.3.18\spring-core-5.3.18.jar;D:\Tools\repo\org\springframework\spring-jcl\5.3.18\spring-jcl-5.3.18.jar;D:\Tools\repo\com\google\guava\guava\31.1-jre\guava-31.1-jre.jar;D:\Tools\repo\com\google\guava\failureaccess\1.0.1\failureaccess-1.0.1.jar;D:\Tools\repo\com\google\guava\listenablefuture\9999.0-empty-to-avoid-conflict-with-guava\listenablefuture-9999.0-empty-to-avoid-conflict-with-guava.jar;D:\Tools\repo\com\google\code\findbugs\jsr305\3.0.2\jsr305-3.0.2.jar;D:\Tools\repo\org\checkerframework\checker-qual\3.12.0\checker-qual-3.12.0.jar;D:\Tools\repo\com\google\errorprone\error_prone_annotations\2.11.0\error_prone_annotations-2.11.0.jar;D:\Tools\repo\com\google\j2objc\j2objc-annotations\1.3\j2objc-annotations-1.3.jar;D:\Tools\repo\joda-time\joda-time\2.9.9\joda-time-2.9.9.jar com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo 20:53:22.696 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【1】 20:53:22.696 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【2】 20:53:22.696 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【0】 20:53:23.707 [pool-1-thread-5] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【4】 20:53:23.707 [pool-1-thread-6] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【5】 20:53:23.707 [pool-1-thread-7] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【6】 20:53:24.711 [pool-1-thread-13] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【12】 20:53:24.711 [pool-1-thread-8] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【7】 20:53:24.711 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【3】 20:53:25.726 [pool-1-thread-9] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【8】 20:53:25.726 [pool-1-thread-12] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【11】 20:53:25.726 [pool-1-thread-14] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【13】 20:53:26.738 [pool-1-thread-16] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【15】 20:53:26.738 [pool-1-thread-11] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【10】 20:53:26.738 [pool-1-thread-10] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【9】 20:53:27.741 [pool-1-thread-18] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【17】 20:53:27.741 [pool-1-thread-17] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【16】 20:53:27.741 [pool-1-thread-15] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【14】 20:53:28.741 [pool-1-thread-19] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【18】 20:53:28.741 [pool-1-thread-20] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo - num=【19】 Process finished with exit code 0通过结果可以看到，每秒只打印2个数字，就是信号量控制的。示例二同时获取多个许可，释放多个许可，也可以一个一个释放许可。下面代码示例，只有2个并发线程所有，获取后没有了，就类似单线程。package com.yanxizhu.demo.concurrency.aqs; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: Semaphore-信号量，控制线程并发数，可以获取或释放多个许可 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 20:41 * @version: 1.0 */ @Slf4j @ThreadSafety public class SemaphoreDemo2 { private static final int threadNum = 20; private static final int currentThreadNum = 3; public static void main(String[] args) throws InterruptedException { //线程池 ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 Semaphore semaphore = new Semaphore(currentThreadNum); for (int i = 0; i <threadNum; i++) { final int num = i; executorService.execute(() -> { try{ //获取3个许可，需要等3个都执行完了，才释放3个许可 semaphore.acquire(3); pringNum(num); //释放3个许可 semaphore.release(3); }catch (Exception e){ log.error("执行错误【{}】", e.getMessage()); } }); } executorService.shutdown(); } public static void pringNum(int num) throws InterruptedException { log.info("num=【{}】", num); Thread.sleep(1000); } }输出结果：20:56:17.733 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【0】 20:56:18.740 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【1】 20:56:19.754 [pool-1-thread-6] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【5】 20:56:20.755 [pool-1-thread-7] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【6】 20:56:21.767 [pool-1-thread-10] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【9】 20:56:22.780 [pool-1-thread-8] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【7】 20:56:23.791 [pool-1-thread-5] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【4】 20:56:24.800 [pool-1-thread-9] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【8】 20:56:25.801 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【3】 20:56:26.812 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【2】 20:56:27.824 [pool-1-thread-11] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【10】 20:56:28.834 [pool-1-thread-12] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【11】 20:56:29.847 [pool-1-thread-13] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【12】 20:56:30.850 [pool-1-thread-14] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【13】 20:56:31.853 [pool-1-thread-17] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【16】 20:56:32.863 [pool-1-thread-15] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【14】 20:56:33.873 [pool-1-thread-16] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【15】 20:56:34.885 [pool-1-thread-18] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【17】 20:56:35.885 [pool-1-thread-19] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【18】 20:56:36.897 [pool-1-thread-20] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo2 - num=【19】 Disconnected from the target VM, address: '127.0.0.1:13050', transport: 'socket'示例三当线程数超过并发数，就丢失多余的。package com.yanxizhu.demo.concurrency.aqs; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: Semaphore-信号量，控制线程并发数，超过并发量时掉漆多余线程 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 20:41 * @version: 1.0 */ @Slf4j @ThreadSafety public class SemaphoreDemo3 { private static final int threadNum = 20; private static final int currentThreadNum = 3; public static void main(String[] args) throws InterruptedException { //线程池 ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 Semaphore semaphore = new Semaphore(currentThreadNum); for (int i = 0; i <threadNum; i++) { final int num = i; executorService.execute(() -> { try{ //尝试获取许可，获取到才执行 if (semaphore.tryAcquire()) { pringNum(num); //释放一个许可 semaphore.release(); } }catch (Exception e){ log.error("执行错误【{}】", e.getMessage()); } }); } executorService.shutdown(); } public static void pringNum(int num) throws InterruptedException { log.info("num=【{}】", num); Thread.sleep(1000); } }输出结果：21:04:48.376 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo3 - num=【0】 21:04:49.387 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo3 - num=【1】 Disconnected from the target VM, address: '127.0.0.1:2839', transport: 'socket'只输出2个线程，其它18个线程被丢弃。tryAcquire方法重载说明：//无参 public boolean tryAcquire() { return sync.nonfairTryAcquireShared(1) >= 0; } //1个参数，获取许可个数 public boolean tryAcquire(int permits) { if (permits < 0) throw new IllegalArgumentException(); return sync.nonfairTryAcquireShared(permits) >= 0; } //2个参数，超时时间，单位 public boolean tryAcquire(long timeout, TimeUnit unit) throws InterruptedException { return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout)); } //3个参数，获取许可个数，超时时间，单位 public boolean tryAcquire(int permits, long timeout, TimeUnit unit) throws InterruptedException { if (permits < 0) throw new IllegalArgumentException(); return sync.tryAcquireSharedNanos(permits, unit.toNanos(timeout)); }示例四设置超时时间package com.yanxizhu.demo.concurrency.aqs; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; 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; /** * @description: Semaphore-信号量，控制线程并发数，带超时时间限制的 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 20:41 * @version: 1.0 */ @Slf4j @ThreadSafety public class SemaphoreDemo4 { private static final int threadNum = 50; private static final int currentThreadNum = 3; public static void main(String[] args) throws InterruptedException { //线程池 ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 Semaphore semaphore = new Semaphore(currentThreadNum); for (int i = 0; i <threadNum; i++) { final int num = i; executorService.execute(() -> { try{ //尝试获取许可，获取到才执行，获取超过3秒，就不执行了。 if (semaphore.tryAcquire(3000, TimeUnit.MILLISECONDS)) { pringNum(num); //释放一个许可 semaphore.release(); } }catch (Exception e){ log.error("执行错误【{}】", e.getMessage()); } }); } executorService.shutdown(); } public static void pringNum(int num) throws InterruptedException { log.info("num=【{}】", num); Thread.sleep(1000); } }输出结果：22:01:36.804 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【0】 22:01:36.804 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【2】 22:01:36.804 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【1】 22:01:37.828 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【3】 22:01:37.828 [pool-1-thread-6] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【5】 22:01:37.828 [pool-1-thread-10] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【9】 22:01:38.843 [pool-1-thread-12] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【11】 22:01:38.843 [pool-1-thread-13] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【12】 22:01:38.843 [pool-1-thread-8] INFO com.yanxizhu.demo.concurrency.aqs.SemaphoreDemo4 - num=【7】 Disconnected from the target VM, address: '127.0.0.1:11385', transport: 'socket'3、CyclicBarrier允许一组线程相互等待，直到达到某个共同屏障点，直到每个线程都就绪后面的才继续往下执行。和CoutDownLatch相似都是通过计数器来实现的，图从下往上看的。线程释放后可以循环使用，因此也叫循环屏障。CoutDownLatch用户分计算，汇总最后的结果。示例一package com.yanxizhu.demo.concurrency.aqs; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.BrokenBarrierException; import java.util.concurrent.CyclicBarrier; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * @description: CyclicBarrier 实现线程相互等待 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 22:15 * @version: 1.0 */ @Slf4j public class CyclicBarrierDemo { //定义需要相互等待5个线程，就绪后才执行，后面的代码 private static final CyclicBarrier cyclicBarrier = new CyclicBarrier(4); public static void main(String[] args) throws Exception{ //线程池 ExecutorService executorService = Executors.newCachedThreadPool(); for (int i = 0; i < 10; i++) { final int threadNum = i; //模式看效果，等待1秒 Thread.sleep(1000); executorService.execute(() -> { try { pringWait(threadNum); } catch (Exception e) { log.error("执行出错了。。。", e.getMessage()); } }); } executorService.shutdown(); } public static void pringWait(int threadNum) throws InterruptedException, BrokenBarrierException { //模式看效果，等待1秒 Thread.sleep(1000); log.info("等待中。。。{}", threadNum); //告诉线程每个就绪了，await方法支持传入超时时间 //可选参数long timeout, TimeUnit unit cyclicBarrier.await(); //就绪后才执行 log.info("开始执行了。。{}",threadNum); } }输出结果：Connected to the target VM, address: '127.0.0.1:14410', transport: 'socket' 22:26:04.855 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。0 22:26:05.853 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。1 22:26:06.866 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。2 22:26:07.881 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。3 22:26:07.881 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。3 22:26:07.882 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。1 22:26:07.882 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。2 22:26:07.881 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。0 22:26:08.896 [pool-1-thread-5] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。4 22:26:09.899 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。5 22:26:10.901 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。6 22:26:11.902 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。7 22:26:11.902 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。7 22:26:11.902 [pool-1-thread-5] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。4 22:26:11.902 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。6 22:26:11.902 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 开始执行了。。5 22:26:12.903 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。8 22:26:13.916 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo - 等待中。。。9 Disconnected from the target VM, address: '127.0.0.1:14410', transport: 'socket'示例二带超时时间的，注意需要trycatch才能不影响后续流程执行。package com.yanxizhu.demo.concurrency.aqs; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.*; /** * @description: CyclicBarrier 实现线程相互等待,带超时时间，注意捕获异常，才能继续执行后面的操作 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 22:15 * @version: 1.0 */ @Slf4j public class CyclicBarrierDemo2 { //定义需要相互等待5个线程，就绪后才执行，后面的代码 private static final CyclicBarrier cyclicBarrier = new CyclicBarrier(4); public static void main(String[] args) throws Exception{ //线程池 ExecutorService executorService = Executors.newCachedThreadPool(); for (int i = 0; i < 10; i++) { final int threadNum = i; //模式看效果，等待1秒 Thread.sleep(1000); executorService.execute(() -> { try { pringWait(threadNum); } catch (Exception e) { log.error("执行出错了。。。", e.getMessage()); } }); } executorService.shutdown(); } public static void pringWait(int threadNum) throws InterruptedException, BrokenBarrierException { //模式看效果，等待1秒 Thread.sleep(1000); log.info("等待中。。。{}", threadNum); //告诉线程每个就绪了，带超时时间 try { cyclicBarrier.await(2000, TimeUnit.MILLISECONDS); } catch (Exception e){ log.warn("超时了，注意：捕获异常，才能继续执行", e.getMessage()); } //就绪后才执行 log.info("开始执行了。。{}",threadNum); } }输出结果：22:37:57.786 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。0 22:37:58.797 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。1 22:37:59.797 [pool-1-thread-1] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:37:59.797 [pool-1-thread-2] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:37:59.797 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。0 22:37:59.798 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。1 22:37:59.812 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。2 22:37:59.812 [pool-1-thread-3] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:37:59.812 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。2 22:38:00.813 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。3 22:38:00.813 [pool-1-thread-1] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:38:00.813 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。3 22:38:01.828 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。4 22:38:01.828 [pool-1-thread-3] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:38:01.828 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。4 22:38:02.840 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。5 22:38:02.840 [pool-1-thread-1] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:38:02.840 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。5 22:38:03.842 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。6 22:38:03.842 [pool-1-thread-3] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:38:03.842 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。6 22:38:04.855 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。7 22:38:04.855 [pool-1-thread-1] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:38:04.855 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。7 22:38:05.870 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。8 22:38:05.870 [pool-1-thread-3] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:38:05.870 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。8 22:38:06.870 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 等待中。。。9 22:38:06.870 [pool-1-thread-1] WARN com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 超时了，注意：捕获异常，才能继续执行 22:38:06.870 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo2 - 开始执行了。。9 Disconnected from the target VM, address: '127.0.0.1:2195', transport: 'socket'示例三构造可以传入runable线程，优先执行。package com.yanxizhu.demo.concurrency.aqs; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.BrokenBarrierException; import java.util.concurrent.CyclicBarrier; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * @description: CyclicBarrier 实现线程相互等待，CyclicBarrier可以传入runable线程，优先执行该部分代码 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/25 22:15 * @version: 1.0 */ @Slf4j public class CyclicBarrierDemo3 { //定义需要相互等待5个线程，就绪后才执行，后面的代码 private static final CyclicBarrier cyclicBarrier = new CyclicBarrier(4, () -> { log.info("相互等待线程都就绪后，这部分代码先执行"); }); public static void main(String[] args) throws Exception{ //线程池 ExecutorService executorService = Executors.newCachedThreadPool(); for (int i = 0; i < 10; i++) { final int threadNum = i; //模式看效果，等待1秒 Thread.sleep(1000); executorService.execute(() -> { try { pringWait(threadNum); } catch (Exception e) { log.error("执行出错了。。。", e.getMessage()); } }); } executorService.shutdown(); } public static void pringWait(int threadNum) throws InterruptedException, BrokenBarrierException { //模式看效果，等待1秒 Thread.sleep(1000); log.info("等待中。。。{}", threadNum); //告诉线程每个就绪了，await方法支持传入超时时间 //可选参数long timeout, TimeUnit unit cyclicBarrier.await(); //就绪后才执行 log.info("开始执行了。。{}",threadNum); } }输出结果：22:42:09.313 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。0 22:42:10.313 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。1 22:42:11.318 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。2 22:42:12.320 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。3 22:42:12.320 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 相互等待线程都就绪后，这部分代码先执行 22:42:12.320 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。3 22:42:12.320 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。2 22:42:12.320 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。1 22:42:12.320 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。0 22:42:13.325 [pool-1-thread-5] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。4 22:42:14.339 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。5 22:42:15.353 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。6 22:42:16.355 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。7 22:42:16.355 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 相互等待线程都就绪后，这部分代码先执行 22:42:16.355 [pool-1-thread-1] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。7 22:42:16.355 [pool-1-thread-5] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。4 22:42:16.355 [pool-1-thread-3] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。5 22:42:16.355 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 开始执行了。。6 22:42:17.358 [pool-1-thread-4] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。8 22:42:18.372 [pool-1-thread-2] INFO com.yanxizhu.demo.concurrency.aqs.CyclicBarrierDemo3 - 等待中。。。9总结：注意CoutDownLatch与CyclicBarrier的不同，对别使用。

线程安全-同步容器 线程安全-同步容器主要包括ArrayList -> Vector，Stack HashMap->HashTable（key、value不能为null）Collections.synchronizedXXX（List、Set、Map）都是使用Synchronized进行修饰的，性能不是特别好。可以使用并发容器代替。注意：同步容器也可能是线程步安全的。同步容器线程步安全，代码示例：package com.yanxizhu.demo.concurrency.synContainer; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import java.util.Vector; /** * @description: 同步容器，也可能出现线程不安全情况 * @author: <a href="mailto:vip@foxmail.com">清风</a> * @date: 2022/4/24 10:32 * @version: 1.0 */ @UnThreadSafety public class DemoVecotNo { private static final Vector<Integer> vector = new Vector<>(); public static void main(String[] args) { //一直循环 while(true) { //向vector容器放入值 for(int i=0; i <10; i++){ vector.add(i); } //线程1，向vector容器移除值 new Thread(()->{ for(int i=0; i <vector.size(); i++){ vector.remove(i); } }).start(); //线程2，向vector中获取值 new Thread(()->{ for(int i=0; i <vector.size(); i++){ vector.get(i); } }).start(); } } }输出结果：Exception in thread "Thread-478" Exception in thread "Thread-1724" Exception in thread "Thread-1918" Exception in thread "Thread-1769" java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 10 at java.base/java.util.Vector.remove(Vector.java:875) at com.yanxizhu.demo.concurrency.synContainer.DemoVecotNo.lambda$main$0(DemoVecotNo.java:27) at java.base/java.lang.Thread.run(Thread.java:834) java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 62 at java.base/java.util.Vector.remove(Vector.java:875) at com.yanxizhu.demo.concurrency.synContainer.DemoVecotNo.lambda$main$0(DemoVecotNo.java:27) at java.base/java.lang.Thread.run(Thread.java:834) java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 2 at java.base/java.util.Vector.get(Vector.java:781) at com.yanxizhu.demo.concurrency.synContainer.DemoVecotNo.lambda$main$1(DemoVecotNo.java:34) at java.base/java.lang.Thread.run(Thread.java:834) java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 10 at java.base/java.util.Vector.remove(Vector.java:875) at com.yanxizhu.demo.concurrency.synContainer.DemoVecotNo.lambda$main$0(DemoVecotNo.java:27) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "Thread-4507" java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 12 at java.base/java.util.Vector.get(Vector.java:781) at com.yanxizhu.demo.concurrency.synContainer.DemoVecotNo.lambda$main$1(DemoVecotNo.java:34) at java.base/java.lang.Thread.run(Thread.java:834)说明：add、remove、get防范都是通过synchronized修饰了的，为什么还是会出现线程不安全，因为当remove和get运行时，如果i相等，remove移除i时，get再获取i就包错了。Vector线程安全代码示例package com.yanxizhu.demo.concurrency.synContainer; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.Vector; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程安全容器：Vector * @author: <a href="mailto:vip@foxmail.com">清风</a> * @date: 2022/4/24 10:18 * @version: 1.0 */ @Slf4j @ThreadSafety public class DeomVecotr { private static Vector<Integer> vector = new Vector<>(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("vector size:{}", vector.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ vector.add(count); } }输出结果：每次是输出5000Hashtable线程安全，代码示例：package com.yanxizhu.demo.concurrency.synContainer; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.HashMap; import java.util.Hashtable; import java.util.Map; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程安全容器：Hashtable * @author: <a href="mailto:vip@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoHashTable { private static Map<Integer, Integer> map = new Hashtable<>(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("map size:{}", map.size()); } private static void update(int count){ map.put(count, count); } }输出结果：每次都是5000.线程安全。Collections.synchronizedList线程安全，同步容器package com.yanxizhu.demo.concurrency.synContainer; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 安全容器，Collections下的同步容器，线程安全 * @author: <a href="mailto:vip@foxmail.com">清风</a> * @date: 2022/4/24 10:47 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoCollections { private static List<Integer> list = Collections.synchronizedList(new ArrayList<>()); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("list size:{}", list.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ list.add(count); } }输出结果：每次输出5000，线程安全。Collections.synchronizedSet线程安全，同步容器，代码示例package com.yanxizhu.demo.concurrency.synContainer; import com.google.common.collect.Sets; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.Collections; import java.util.Set; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 安全容器，Collections下的同步容器，synchronizedSet,线程安全 * @author: <a href="mailto:vip@foxmail.com">清风</a> * @date: 2022/4/24 10:47 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoCollectionsSynSet { private static Set<Integer> set = Collections.synchronizedSet(Sets.newHashSet()); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("set size:{}", set.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ set.add(count); } }输出结果：每次输出5000，线程安全Collections.synchronizedMap线程安全同步容器，代码示例：package com.yanxizhu.demo.concurrency.synContainer; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.Collections; import java.util.HashMap; import java.util.Map; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 安全容器，Collections.synchronizedMap，线程安全 * @author: <a href="mailto:vip@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoCollectionsSynHashMap { private static Map<Integer, Integer> map = Collections.synchronizedMap(new HashMap()); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("map size:{}", map.size()); } private static void update(int count){ map.put(count, count); } }输出结果：每次输出5000，线程安全。常用操作错误package com.yanxizhu.demo.concurrency.synContainer; import java.util.Iterator; import java.util.Vector; /** * @description: 常见容器使用错误，解决办法 * @author: <a href="mailto:vip@foxmail.com">清风</a> * @date: 2022/4/24 11:04 * @version: 1.0 */ public class DemoErrorUser { //增强for循环中修改，报错：java.util.ConcurrentModificationException public static void test1(Vector<Integer> vector) { for (Integer integer: vector) { //使用增强for循环 if (integer.equals(3)) { // vector.remove(integer); vector.add(4); } } } //迭代器中循环修改，报错：java.util.ConcurrentModificationException public static void test2(Vector<Integer> vector) { Iterator<Integer> iterator = vector.iterator(); while (iterator.hasNext()){ Integer integer = iterator.next(); if( integer.equals(3)) { vector.remove(integer); } } } //普通for循环中修改，正常。 public static void test3(Vector<Integer> vector) { for(int i=0; i< vector.size(); i++) { if(i==3) { vector.remove(i); } } } //总结：增强for、迭代器循环中修改，可以先标记，然后最后进行修改。 public static void main(String[] args) { Vector<Integer> vector = new Vector<>(); vector.add(1); vector.add(2); vector.add(3); test1(vector); // test2(vector); // test3(vector); } }输出结果：ConcurrentModificationExceptionException in thread "main" java.util.ConcurrentModificationException at java.base/java.util.Vector$Itr.checkForComodification(Vector.java:1321) at java.base/java.util.Vector$Itr.next(Vector.java:1277) at com.yanxizhu.demo.concurrency.synContainer.DemoErrorUser.test1(DemoErrorUser.java:16) at com.yanxizhu.demo.concurrency.synContainer.DemoErrorUser.main(DemoErrorUser.java:52)增强for、迭代器中循环修改线程报错，正常for循环，正常，解决办法，通过标记后，再单独进行移除操作。

线程不安全的类与写法 线程不安全的类与写法线程不安全的类：类的对象可以同时被多个线程访问，比如抛出异常，逻辑错误。下面介绍一些常见的类。StringBuilderStringBuilder线程不安全的类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全的类：StringBuilder * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:01 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoStringBuilder { //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; //累加总和 private static StringBuilder stringBuilder = new StringBuilder(); public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("字符长度Length=【{}】",stringBuilder.length()); } /** * 累加 */ private static void update(){ stringBuilder.append(1); } }每次输出字符长度不一样，也不等于5000StringBuffer线程安全的类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程安全的类：StringBuffer * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:06 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoStringBuffer { //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; //累加总和 private static StringBuffer stringBuffer = new StringBuffer(); public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("字符长度Length=【{}】", stringBuffer.length()); } /** * 累加 */ private static void update(){ stringBuffer.append(1); } }输出结果：每次都是长度为5000.StringBuffer为什么线程安全，看源码 @Override @HotSpotIntrinsicCandidate public synchronized StringBuffer append(int i) { toStringCache = null; super.append(i); return this; }因为StringBuffer所有的方法操作都加了synchronized。区别StringBuffer由于加了synchronized，性能上有损耗，没有StringBuilder性能高，在线程封闭中，堆栈封闭时，一般处理字符串局部变量时用StringBuilfer就行了。SimpleDateFormat线程不安全的类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类： SimpleDateFormat * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:18 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoSimpleDateFormat { private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyyMMMdd"); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); } /** * 累加 */ private static void update(){ try { simpleDateFormat.parse("20220424"); } catch (ParseException e) { log.error(e.getMessage()); } } }输出结果： at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-824" java.lang.NumberFormatException: For input string: "E.0220E0" at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-717" java.lang.NumberFormatException: multiple points at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1890) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-671" java.lang.NumberFormatException: For input string: "" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Long.parseLong(Long.java:702) at java.base/java.lang.Long.parseLong(Long.java:817) at java.base/java.text.DigitList.getLong(DigitList.java:195) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-805" java.lang.NumberFormatException: multiple points at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1914) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-736" java.lang.NumberFormatException: For input string: ".20220424" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Long.parseLong(Long.java:678) at java.base/java.lang.Long.parseLong(Long.java:817) at java.base/java.text.DigitList.getLong(DigitList.java:195) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-740" java.lang.NumberFormatException: multiple points at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1914) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-695" java.lang.NumberFormatException: For input string: "E.0220" at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-888" java.lang.NumberFormatException: For input string: "202204242022042420220424" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Long.parseLong(Long.java:692) at java.base/java.lang.Long.parseLong(Long.java:817) at java.base/java.text.DigitList.getLong(DigitList.java:195) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834)虽然SimpleDateFormat是线程不安全的类，但是可以通过线程封闭中，堆栈封闭(栈封闭)方法，将SimpleDateFormat定义到局部变量中，每次是一个新对象，这样来保证线程安全。package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类： SimpleDateFormat,通过堆栈封闭，实现线程安全。 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:18 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoSimpleDateFormatOk { //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); } /** * 通过线程封闭，将SimpleDateFormat定义在方法内，每次都是一个新的对象，来保证线程安全 */ private static void update(){ try { SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyyMMMdd"); simpleDateFormat.parse("20220424"); } catch (ParseException e) { log.error(e.getMessage()); } } }输出结果：输出5000条，一样的。09:27:17.633 [pool-1-thread-461] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.633 [pool-1-thread-460] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.634 [pool-1-thread-452] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.634 [pool-1-thread-445] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.634 [pool-1-thread-453] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 。。。。。joda.time第三方包中DateTimeFormatter代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import org.joda.time.DateTime; import org.joda.time.format.DateTimeFormat; import org.joda.time.format.DateTimeFormatter; import java.util.Date; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程安全的类：Joda-time包里面的DateTimeFormatter需要单独导入 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:31 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoJodaTime { private static DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyyyMMdd"); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(clientsTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(concurrencyTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ Date date = DateTime.parse("20220424", dateTimeFormatter).toDate(); log.info("{},{}", count, date); } }输出结果：有5000条，线程安全的09:45:06.164 [pool-1-thread-1947] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 1946,Sun Apr 24 00:00:00 CST 2022 09:45:06.154 [pool-1-thread-491] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 490,Sun Apr 24 00:00:00 CST 2022 09:45:06.184 [pool-1-thread-2943] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 2942,Sun Apr 24 00:00:00 CST 2022 09:45:06.169 [pool-1-thread-1911] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 1910,Sun Apr 24 00:00:00 CST 2022 09:45:06.169 [pool-1-thread-616] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 615,Sun Apr 24 00:00:00 CST 2022 09:45:06.168 [pool-1-thread-2551] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 2550,Sun Apr 24 00:00:00 CST 2022 09:45:06.144 [pool-1-thread-1415] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 1414,Sun Apr 24 00:00:00 CST 2022 09:45:06.154 [pool-1-thread-4611] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 4610,Sun Apr 24 00:00:00 CST 2022 09:45:06.169 [pool-1-thread-4760] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 4759,Sun Apr 24 00:00:00 CST 2022 09:45:06.167 [pool-1-thread-2388] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 2387,Sun Apr 24 00:00:00 CST 2022 09:45:06.184 [pool-1-thread-3990] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 3989,Sun Apr 24 00:00:00 CST 2022 。。。。。ArrayList线程不安全的代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import org.checkerframework.checker.units.qual.A; import org.joda.time.DateTime; import java.util.ArrayList; import java.util.Date; import java.util.List; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类：ArrayList * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoArrayList { private static List<Integer> list = new ArrayList<>(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("list size:{}", list.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ list.add(count); } }输出结果：每次输出ist长度不同，线程不安全的。HashSet线程不安全类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.HashSet; import java.util.Set; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类：HashSet * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoHashSet { private static Set<Integer> set = new HashSet<>(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("set size:{}", set.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ set.add(count); } }输出结果：每次长度不同，不是5000，线程不安全。HashMap线程不安全的代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.*; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类：HashMap * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoHashMap { private static Map<Integer, Integer> map = new HashMap(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("map size:{}", map.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ map.put(count, count); } }输出结果： 长度不是5000，每次长度不一样，线程不安全。总结：线程安全类对应的不只一个。后面专门说明。注意：先检查再执行这种类是线程不安全的，因为被分成2步了，if (condition(a)) { handle(1);}

可见性和有序性 可见性可见性：一个线程对主内存的修改可以及时的被其它线程观察到。导致共享变量在线程间不可见的原因：线程交叉执行重排序结合线程交叉执行共享变量更新后的值没有在工作内存与主存间及时更新可见性-synchronizedJMM关于synchronized的两条规定：线程解锁前，必须把共享变量的最新值刷新到主内存线程加锁时，将清空工作内存中共享变量的值，从而使用共享变量时需要从主内存中重新读取最新的值（注意，加锁与解锁是同一把锁）可见性-volatilevolatile，通过加入内存屏障和禁止重排序优化来实现。对volatile变量写操作时，会在写操作后加入一条store屏障指令，将本地内存中的共享变量值刷新到主内存对volatile变量读操作时，会在读操作前加入一条load屏障指令，从主内存中读取共享变量volatile写：volatile读：有序性Java内存模型中，允许编译器和处理器对指令进行重排序，但是重排序过程不会影响到单线程程序的执行，却会影响到多线程并发执行的正确性.可通过volatile、synchronized、Lock保证有序性。有序性-happens-before原则程序次序规则：一个线程内，按照代码顺序，书写在前面的操作先行发生于书写在后面的操作锁定规则：一个unLock操作先行发生于后面对同一个锁的lock操作volatile变量规则：对一个变量的写操作先行发生于后面对这个变量的读操作传递规则：如果操作A先行发生于操作B，而操作B又先行发生于操作C，则可以得出操作A先行发生于操作C线程启动规则：Thread对象的start（）方法先行发生于此线程的每一个动作线程中断规则：对线程interrupt（）方法的调用先行发生于被中断线程的代码检测到中断事件的发生线程终结规则：线程中所有的操作都先行发生于线程的终止检测，我们可以通过Thread.join（）方法结束、Thread.isAlive（）的返回值手段检测到线程已经终止执行对象终结规则：一个对象的初始化完成先行发生于他的finalize（）方法的开始线程安全性-总结原子性：Atomic包、CAS算法、synchronized、Lock可见性：synchronized、volatile有序性：happens-before

线程八锁 线程八锁package com.yanxizhu; /* * 题目：判断打印的 "one" or "two" ？ * * 1. 两个普通同步方法，两个线程，标准打印， 打印? //one two * 2. 新增 Thread.sleep() 给 getOne() ,打印? //one two * 3. 新增普通方法 getThree() , 打印? //three one two * 4. 两个普通同步方法，两个 Number 对象，打印? //two one * 5. 修改 getOne() 为静态同步方法，打印? //two one * 6. 修改两个方法均为静态同步方法，一个 Number 对象? //one two * 7. 一个静态同步方法，一个非静态同步方法，两个 Number 对象? //two one * 8. 两个静态同步方法，两个 Number 对象? //one two * * 线程八锁的关键： * ①非静态方法的锁默认为 this, 静态方法的锁为 对应的 Class 实例 * ②某一个时刻内，只能有一个线程持有锁，无论几个方法。 */ public class TestThread8Monitor { public static void main(String[] args) { Number number = new Number(); Number number2 = new Number(); new Thread(new Runnable() { @Override public void run() { number.getOne(); } }).start(); new Thread(new Runnable() { @Override public void run() { //number.getTwo(); number2.getTwo(); } }).start(); /*new Thread(new Runnable() { @Override public void run() { number.getThree(); } }).start();*/ } } class Number{ public static synchronized void getOne(){//Number.class try { Thread.sleep(3000); } catch (InterruptedException e) { } System.out.println("one"); } public synchronized void getTwo(){//this System.out.println("two"); } public void getThree(){ System.out.println("three"); } }一个对象里面如果有多个synchronized方法，某一个时刻内，只要一个线程去调用 其中的一个synchronized方法了，其它的线程都只能等待，换句话说，某一个时刻 内，只能有唯一一个线程去访问这些synchronized方法锁的是当前对象this，被锁定后，其它的线程都不能进入到当前对象的其它的 synchronized方法加个普通方法后发现和同步锁无关换成两个对象后，不是同一把锁了，情况立刻变化。都换成静态同步方法后，情况又变化所有的非静态同步方法用的都是同一把锁——实例对象本身，也就是说如果一个实 例对象的非静态同步方法获取锁后，该实例对象的其他非静态同步方法必须等待获 取锁的方法释放锁后才能获取锁，可是别的实例对象的非静态同步方法因为跟该实 例对象的非静态同步方法用的是不同的锁，所以毋须等待该实例对象已获取锁的非 静态同步方法释放锁就可以获取他们自己的锁。所有的静态同步方法用的也是同一把锁——类对象本身，这两把锁是两个不同的对 象，所以静态同步方法与非静态同步方法之间是不会有竞态条件的。但是一旦一个 静态同步方法获取锁后，其他的静态同步方法都必须等待该方法释放锁后才能获取 锁，而不管是同一个实例对象的静态同步方法之间，还是不同的实例对象的静态同 步方法之间，只要它们同一个类的实例对象！

ScheduledThreadPool线程调度 ScheduledThreadPool线程调度package com.yanxizhu; import java.util.Random; import java.util.concurrent.Callable; import java.util.concurrent.Executors; import java.util.concurrent.Future; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; /* * 一、线程池：提供了一个线程队列，队列中保存着所有等待状态的线程。避免了创建与销毁额外开销，提高了响应的速度。 * * 二、线程池的体系结构： * java.util.concurrent.Executor : 负责线程的使用与调度的根接口 * |--**ExecutorService 子接口: 线程池的主要接口 * |--ThreadPoolExecutor 线程池的实现类 * |--ScheduledExecutorService 子接口：负责线程的调度 * |--ScheduledThreadPoolExecutor ：继承 ThreadPoolExecutor， 实现 ScheduledExecutorService * * 三、工具类 : Executors * ExecutorService newFixedThreadPool() : 创建固定大小的线程池 * ExecutorService newCachedThreadPool() : 缓存线程池，线程池的数量不固定，可以根据需求自动的更改数量。 * ExecutorService newSingleThreadExecutor() : 创建单个线程池。线程池中只有一个线程 * * ScheduledExecutorService newScheduledThreadPool() : 创建固定大小的线程，可以延迟或定时的执行任务。 */ public class TestScheduledThreadPool { public static void main(String[] args) throws Exception { ScheduledExecutorService pool = Executors.newScheduledThreadPool(5); for (int i = 0; i < 5; i++) { Future<Integer> result = pool.schedule(new Callable<Integer>(){ @Override public Integer call() throws Exception { int num = new Random().nextInt(100);//生成随机数 System.out.println(Thread.currentThread().getName() + " : " + num); return num; } }, 1, TimeUnit.SECONDS); System.out.println(result.get()); } pool.shutdown(); } }

Executor线程池 Executors线程池package com.yanxizhu; import java.util.ArrayList; import java.util.List; import java.util.concurrent.Callable; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; /* * 一、线程池：提供了一个线程队列，队列中保存着所有等待状态的线程。避免了创建与销毁额外开销，提高了响应的速度。 * * 二、线程池的体系结构： * java.util.concurrent.Executor : 负责线程的使用与调度的根接口 * |--**ExecutorService 子接口: 线程池的主要接口 * |--ThreadPoolExecutor 线程池的实现类 * |--ScheduledExecutorService 子接口：负责线程的调度 * |--ScheduledThreadPoolExecutor ：继承 ThreadPoolExecutor， 实现 ScheduledExecutorService * * 三、工具类 : Executors * ExecutorService newFixedThreadPool() : 创建固定大小的线程池 * ExecutorService newCachedThreadPool() : 缓存线程池，线程池的数量不固定，可以根据需求自动的更改数量。 * ExecutorService newSingleThreadExecutor() : 创建单个线程池。线程池中只有一个线程 * * ScheduledExecutorService newScheduledThreadPool() : 创建固定大小的线程，可以延迟或定时的执行任务。 */ public class TestThreadPool { public static void main(String[] args) throws Exception { //1. 创建线程池 ExecutorService pool = Executors.newFixedThreadPool(5); List<Future<Integer>> list = new ArrayList<>(); for (int i = 0; i < 10; i++) { Future<Integer> future = pool.submit(new Callable<Integer>(){ @Override public Integer call() throws Exception { int sum = 0; for (int i = 0; i <= 100; i++) { sum += i; } return sum; } }); list.add(future); } pool.shutdown(); for (Future<Integer> future : list) { System.out.println(future.get()); } /*ThreadPoolDemo tpd = new ThreadPoolDemo(); //2. 为线程池中的线程分配任务 for (int i = 0; i < 10; i++) { pool.submit(tpd); } //3. 关闭线程池 pool.shutdown();*/ } // new Thread(tpd).start(); // new Thread(tpd).start(); } class ThreadPoolDemo implements Runnable{ private int i = 0; @Override public void run() { while(i <= 100){ System.out.println(Thread.currentThread().getName() + " : " + i++); } } }

ReadWriteLock读写锁 读写锁package com.yanxizhu; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; /** * @description: 读写锁(互斥锁) * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/19 15:23 * @version: 1.0 */ public class ReadWriteDemo { public static void main(String[] args) { ReadWriteTest readWriteTest = new ReadWriteTest(); new Thread(()->{ readWriteTest.write((int) (Math.random()*101)); },"写锁").start(); for(int i=1;i<50;i++){ new Thread(()->{ readWriteTest.get(); },"读锁").start(); } } } class ReadWriteTest{ int num =0; private ReadWriteLock readWriteLock = new ReentrantReadWriteLock(); //读 public void get(){ readWriteLock.readLock().lock(); try{ System.out.println(num+"=="+Thread.currentThread().getName()); }finally { readWriteLock.readLock().unlock(); } } //写 public void write(int i){ readWriteLock.writeLock().lock(); try{ this.num=i; }finally { readWriteLock.writeLock().unlock(); } } }