Callable() Callable()可以有返回值，可以抛出异常Callable通过Runnable接口的实现类FetuerTask调用线程package com.sw.callable; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.FutureTask; /** * @Author suaxi * @Date 2021/2/12 21:24 */ public class callableTest { public static void main(String[] args) throws ExecutionException, InterruptedException { MyThread thread = new MyThread(); FutureTask futureTask = new FutureTask(thread); //适配类 new Thread(futureTask,"A").start(); new Thread(futureTask,"B").start(); /* call()方法测试 泛型的参数 = 方法的返回值 相同的两个线程运行后只返回一个结果（有缓存） */ Object o = futureTask.get(); //获取callable返回值，此处的get可能会产生阻塞，接收返回值时可能需要等待 System.out.println(o); } } class MyThread implements Callable<String>{ @Override public String call(){ System.out.println("call()方法测试"); return "泛型的参数 = 方法的返回值"; } }

集合不安全问题 集合类不安全List不安全package com.sw.unsafe; import java.util.*; import java.util.concurrent.CopyOnWriteArrayList; /** * @Author suaxi * @Date 2021/1/4 17:12 * java.util.ConcurrentModificationException 并发修改异常 */ public class ListTest { public static void main(String[] args) { /* 并发情况下ArrayList不安全 解决方案： 1、List<String> list = new Vector<>(); 2、List<String> list = Collections.synchronizedList(new ArrayList<>()); 3、List<String> list = new CopyOnWriteArrayList<>(); CopyOnWrite 写入时复制（是一种优化策略） 多个线程调用的时候可能存在写入覆盖问题，读取没问题 CopyOnWrite在写入的时候复制一份给调用者，调用者写入新的数据完成之 后再把之前复制的数据放回原来的位置，保证线程的安全，以此避免了写入覆盖问题 相较于Vector，它没有采用synchronized锁，而是采用Lock锁，效率更高 */ List<String> list = new CopyOnWriteArrayList<>(); for (int i = 0; i < 100; i++) { new Thread(() ->{ list.add(UUID.randomUUID().toString().substring(0,5)); System.out.println(list); },String.valueOf(i)).start(); } } } Set不安全package com.sw.unsafe; import java.util.*; import java.util.concurrent.CopyOnWriteArraySet; /** * @Author suaxi * @Date 2021/1/4 22:08 * java.util.ConcurrentModificationException 并发修改异常 * 解决方法： * 1、Set<String> set = Collections.synchronizedSet(new HashSet<>()); * 2、Set<String> set = new CopyOnWriteArraySet<>(); */ public class SetTest { public static void main(String[] args) { Set<String> set = new CopyOnWriteArraySet<>(); for (int i = 0; i < 30; i++) { new Thread(() ->{ set.add(UUID.randomUUID().toString().substring(0,5)); System.out.println(set); },String.valueOf(i)).start(); } } } hashSet底层是什么？public HashSet(){ map = new HashMap<>(); } //源码 //set add的本质就是map public boolean add(E e) { return map.put(e, PRESENT)==null; } //PRESENT是静态终类 private static final Object PRESENT = new Object();Map不安全package com.sw.unsafe; import java.util.HashMap; import java.util.Map; import java.util.UUID; import java.util.concurrent.ConcurrentHashMap; /** * @Author suaxi * @Date 2021/1/4 22:26 * java.util.ConcurrentModificationException * 解决方法： * Map<String, String> map = new ConcurrentHashMap<>(); */ public class MapTest { public static void main(String[] args) { //默认等价于？ new HashMap<>(16,0.75); Map<String, String> map = new ConcurrentHashMap<>(); for (int i = 0; i < 30; i++) { new Thread(() ->{ map.put(Thread.currentThread().getName(),UUID.randomUUID().toString().substring(0,5)); System.out.println(map); },String.valueOf(i)).start(); } } }

8锁问题 8锁问题什么是锁？锁的对象是谁？package com.sw.lock8; import java.util.concurrent.TimeUnit; /** * @Author suaxi * @Date 2021/1/4 15:44 * 1、执行顺序：发短信 打电话 * 2、增加睡眠时间后，执行顺序：发短信 打电话 */ public class Test1 { public static void main(String[] args) { Phone1 phone1 = new Phone1(); new Thread(() ->{ phone1.sms(); },"A").start(); try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); } new Thread(() ->{ phone1.call(); },"B").start(); } } class Phone1{ //synchronized锁的对象是方法的调用者 //两个方法用的是同一个锁，谁先拿到锁，谁先调用 public synchronized void sms(){ try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("发短信"); } public synchronized void call(){ System.out.println("打电话"); } }package com.sw.lock8; import java.util.concurrent.TimeUnit; /** * @Author suaxi * @Date 2021/1/4 15:51 * 3、增加一个hello的普通方法后，执行顺序为 hello 发短信 * 4、两个对象、两个同步方式，执行顺序为 打电话 发短信 */ public class Test2 { public static void main(String[] args) { //两个对象、两个调用者、两把锁 Phone2 phone1 = new Phone2(); Phone2 phone2 = new Phone2(); new Thread(() ->{ phone1.sms(); },"A").start(); try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); } new Thread(() ->{ phone2.call(); },"B").start(); } } class Phone2{ //synchronized锁的对象是方法的调用者 public synchronized void sms(){ try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("发短信"); } public synchronized void call(){ System.out.println("打电话"); } //普通方法不受锁的限制 public void hello(){ System.out.println("hello"); } }package com.sw.lock8; import java.util.concurrent.TimeUnit; /** * @Author suaxi * @Date 2021/1/4 15:58 * 5、增加static后，执行顺序为 发短信 打电话 * 6、两个Phone对象，执行顺序依然为为 发短信 打电话 */ public class Test3 { public static void main(String[] args) { //两个对象的Class类模板只有一个，与问题5一样锁的也是Class Phone3 phone = new Phone3(); Phone3 phone1 = new Phone3(); new Thread(() ->{ phone.sms(); },"A").start(); try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); } new Thread(() ->{ phone1.call(); },"B").start(); } } class Phone3{ //synchronized锁的对象是方法的调用者 //static静态方法，类一加载就有了，此处锁的是Class对象 public static synchronized void sms(){ try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("发短信"); } public static synchronized void call(){ System.out.println("打电话"); } }package com.sw.lock8; import java.util.concurrent.TimeUnit; /** * @Author suaxi * @Date 2021/1/4 16:05 * 7、1个静态同步方法，1个普通同步方法，一个对象，执行顺序 打电话 发短信 * 8、1个静态同步方法，1个普通同步方法，两个对象，执行顺序 打电话 发短信 */ public class Test4 { public static void main(String[] args) { //两个对象的Class类模板只有一个，与问题5一样锁的也是Class Phone4 phone1 = new Phone4(); Phone4 phone2 = new Phone4(); new Thread(() ->{ phone1.sms(); },"A").start(); try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); } new Thread(() ->{ phone2.call(); },"B").start(); } } class Phone4{ //静态同步方法 锁的是Class类模板 public static synchronized void sms(){ try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("发短信"); } //普通同步方法 锁的是调用者，不需要再等待发短信的sleep睡眠时间，两个方法用的不是同一个锁 public synchronized void call(){ System.out.println("打电话"); } }小结一个对象，拿的是同一把锁两个对象拿的是不同的锁加了static静态方法之后，不论有几个对象，锁的只有一个Class模板普通方法不受锁的限制

生产者和消费者问题 生产者和消费者问题package com.sw.pc; /** * @Author suaxi * @Date 2021/1/4 14:25 */ public class A { public static void main(String[] args) { Data data = new Data(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data.incr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"A").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data.decr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"B").start(); } } class Data{ private int num = 0; //+1 public synchronized void incr() throws InterruptedException { if (num!=0){ //等待 this.wait(); } num++; System.out.println(Thread.currentThread().getName()+"===>"+num); //通知 this.notifyAll(); } //-1 public synchronized void decr() throws InterruptedException { if (num==0){ //等待 this.wait(); } num--; System.out.println(Thread.currentThread().getName()+"===>"+num); //通知 this.notifyAll(); } } 当增加多个线程时（A，B，C，D），会出现虚假唤醒的问题虚假唤醒：线程可以被唤醒，但不会被通知、中断或超时解决方法：将if判断换为whilepackage com.sw.pc; /** * @Author suaxi * @Date 2021/1/4 14:25 */ public class A { public static void main(String[] args) { Data data = new Data(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data.incr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"A").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data.decr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"B").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data.incr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"C").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data.decr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"D").start(); } } class Data{ private int num = 0; //+1 public synchronized void incr() throws InterruptedException { while (num!=0){ //等待 this.wait(); } num++; System.out.println(Thread.currentThread().getName()+"===>"+num); //通知 this.notifyAll(); } //-1 public synchronized void decr() throws InterruptedException { while (num==0){ //等待 this.wait(); } num--; System.out.println(Thread.currentThread().getName()+"===>"+num); //通知 this.notifyAll(); } } JUC版生产者消费者问题使用了Condition接口下的await()等待和signalAll()通知package com.sw.pc; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @Author suaxi * @Date 2021/1/4 14:55 */ public class B { public static void main(String[] args) { Data1 data1 = new Data1(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data1.incr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"A").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data1.decr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"B").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data1.incr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"C").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { try { data1.decr(); } catch (InterruptedException e) { e.printStackTrace(); } } },"D").start(); } } class Data1{ private int num = 0; Lock lock = new ReentrantLock(); Condition condition = lock.newCondition(); //+1 public void incr() throws InterruptedException { try { lock.lock(); //加锁 while (num!=0){ //等待 condition.await(); } num++; System.out.println(Thread.currentThread().getName()+"===>"+num); //通知 condition.signalAll(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); //解锁 } } //-1 public void decr() throws InterruptedException { try { lock.lock(); //加锁 while (num==0){ //等待 condition.await(); } num--; System.out.println(Thread.currentThread().getName()+"===>"+num); //通知 condition.signalAll(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); //解锁 } } }Condition精准通知与线程唤醒可以看到之前的线程执行顺序是无序的。package com.sw.pc; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @Author suaxi * @Date 2021/1/4 15:08 * Condition精准通知与线程唤醒 * ABC三个人互相打电话，A->B,B->C,C->A顺序执行 */ public class C { public static void main(String[] args) { Data2 data2 = new Data2(); new Thread(() ->{ for (int i = 0; i < 10; i++) { data2.CallA(); } },"A").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { data2.CallB(); } },"B").start(); new Thread(() ->{ for (int i = 0; i < 10; i++) { data2.CallC(); } },"C").start(); } } class Data2{ private int num = 1; // 1A 2B 3C private Lock lock = new ReentrantLock(); Condition condition1 = lock.newCondition(); Condition condition2 = lock.newCondition(); Condition condition3 = lock.newCondition(); public void CallA(){ try { lock.lock(); //加锁 while (num!=1){ //等待 condition1.await(); } num = 2; System.out.println(Thread.currentThread().getName()+"===>A打完了"); //通知 condition2.signal(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); //解锁 } } public void CallB(){ try { lock.lock(); //加锁 while (num!=2){ //等待 condition2.await(); } num = 3; System.out.println(Thread.currentThread().getName()+"===>B打完了"); //通知 condition3.signal(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); //解锁 } } public void CallC(){ try { lock.lock(); //加锁 while (num!=3){ //等待 condition3.await(); } num = 1; System.out.println(Thread.currentThread().getName()+"===>C打完了"); //通知 condition1.signal(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); //解锁 } } } 通过不同的监视器监视线程来达到精准通知与线程唤醒的目的

Lock锁 Lock锁传统synchronized锁package com.sw; /** * @Author suaxi * @Date 2021/1/4 14:00 */ public class SaleTicket01 { public static void main(String[] args) { Ticket1 ticket1 = new Ticket1(); new Thread(() ->{for (int i = 0; i < 30; i++) ticket1.sale();},"A").start(); new Thread(() ->{for (int i = 0; i < 30; i++) ticket1.sale();},"B").start(); new Thread(() ->{for (int i = 0; i < 30; i++) ticket1.sale();},"C").start(); } } //synchronized锁 class Ticket1{ private int num = 30; public synchronized void sale(){ if (num>0){ System.out.println(Thread.currentThread().getName()+"卖了"+(num--)+"张票，剩余："+num); } } } Lock接口公平锁：先来后到非公平锁：可以插队（默认使用）package com.sw; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @Author suaxi * @Date 2021/1/4 11:28 */ public class SaleTicket02 { public static void main(String[] args) { Ticket ticket = new Ticket(); new Thread(() ->{for (int i = 0; i < 30; i++) ticket.sale();},"A").start(); new Thread(() ->{for (int i = 0; i < 30; i++) ticket.sale();},"B").start(); new Thread(() ->{for (int i = 0; i < 30; i++) ticket.sale();},"C").start(); } } //Lock锁 class Ticket{ private int num = 30; //1.新建重入锁 Lock lock = new ReentrantLock(); public void sale(){ lock.lock(); //2.加锁 try{ //业务代码 if (num>0){ System.out.println(Thread.currentThread().getName()+"卖了"+(num--)+"张票，剩余："+num); } }catch (Exception e){ e.printStackTrace(); }finally { lock.unlock(); //3.解锁 } } } synchronized与Lock的区别1、synchronized 是内置的Java关键字；Lock是一个Java类2、synchronized 无法判断 获取锁 的状态；Lock可以判断3、synchronized 会自动释放锁；Lock必须手动释放，如果不释放，会产生死锁问题4、synchronized 线程1（获得锁，阻塞），线程2（一直傻傻的等待）；Lock锁就不一定会一直等待下去lock.trylock()5、synchronized 可重入锁，不可中断，非公平；Lock 可重入锁，可以判断锁的状态，非公平（可自定义公平性）6、synchronized 适用于锁少量的同步代码问题；Lock 适合大量同步代码问题