JUC

如何了解JUC

源码 + 官方文档（面试高频问

java.util 工具包，分类

Runnable 没有返回值，效率相比Callable相对较低

java默认有两个线程；

Java本身不能开启线程

public synchronized void start() {
        /**
         * This method is not invoked for the main method thread or "system"
         * group threads created/set up by the VM. Any new functionality added
         * to this method in the future may have to also be added to the VM.
         *
         * A zero status value corresponds to state "NEW".
         */
        if (threadStatus != 0)
            throw new IllegalThreadStateException();

        /* Notify the group that this thread is about to be started
         * so that it can be added to the group's list of threads
         * and the group's unstarted count can be decremented. */
        group.add(this);

        boolean started = false;
        try {
            start0();
            started = true;
        } finally {
            try {
                if (!started) {
                    group.threadStartFailed(this);
                }
            } catch (Throwable ignore) {
                /* do nothing. If start0 threw a Throwable then
                  it will be passed up the call stack */
            }
        }
    }

    private native void start0();

    /**
     * If this thread was constructed using a separate
     * Runnable run object, then that
     * Runnable object's run method is called;
     * otherwise, this method does nothing and returns.
     * 

     * Subclasses of Thread should override this method.
     *
     * @see     #start()
     * @see     #stop()
     * @see     #Thread(ThreadGroup, Runnable, String)
     */
    @Override
    public void run() {
        if (target != null) {
            target.run();
        }
    }
	//本地方法，底层是C++,java无法直接操作硬件
	private native void start0();

线程/进程

线程有几个状态

public enum State {
       //新生
        NEW,

       //运行
        RUNNABLE,

       //阻塞
        BLOCKED,

      //等待，死死等待
        WAITING,

       //超时等待
        TIMED_WAITING,

        //终止
        TERMINATED;
    }

wait和sleep的区别

1. 来自不同的类

   • wait ：Object
   • sleep：Thread

2. 关于锁的释放

   wait会释放锁，sleep睡觉了，不释放锁

3. 使用的范围是不同的

   wait：必须在同步代码块中使用

   sleep：可以在任何地方

4. 是否需要捕获异常

   • wait：不需要捕获异常
   • sleep：需要捕获异常

Lock锁（重点

传统synchronized

本质是：队列

Lock 接口

• 公平锁：十分公平，可以先来后到
• 非公平锁：十分不公平，可以插队(默认)

Lock三部曲

1. new ReentrantLock()
2. lock.lock()
3. finally=> lock.unlock()//解锁

synchronized和Lock锁的区别

• synchronized 内置的java关键字，Lock是一个Java类
• synchronized 无法判断获取锁的状态，Lock可以判断获取到锁的状态
• synchronized 会自动释放锁，Lock必须手动释放锁，如果不释放会死锁
• synchronized 线程1获取锁，线程2会一直等待。Lock不一定会等待下去
• synchronized 可重入锁，不可中断，非公平。Lock，可重入锁，可以判断锁，非公平(可以自己设置)
• synchronized 适合锁少量的代码同步问题，Lock适合锁大量的同步代码

生产者，消费者：判断等待，业务，通知

package com.chen.pc;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/14 0:10
 * @Version V1.0
 **/

public class OldLock {

    public static void main(String[] args) {

        Data1 data = new Data1();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.increament();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"A").start();


        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.increament();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"B").start();


        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.decrement();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"C").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.decrement();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"D").start();

    }
}

class Data1{
    private int number = 0;

    public synchronized void increament() throws Exception{
            //业务代码
            while (number!= 0){
                //等待
                this.wait();
            }
            number++;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            //通知其他线程我+1完毕了
            this.notifyAll();
    }

    public synchronized void decrement() throws Exception{
            //业务代码
            while (number == 0){
                this.wait();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            //通知其他线程我减一完毕了
            this.notifyAll();
    }
}

业务代码需要在每次循环进入的适合等待，不能用if

JUC版的生产者消费者问题

通过Lock找到Condition

package com.chen.pc;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/14 0:10
 * @Version V1.0
 **/

public class jucPC {

    public static void main(String[] args) {

        final Data data = new Data();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.increament();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"A").start();


        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.increament();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"B").start();


        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.decrement();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"C").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try{
                    data.decrement();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        },"D").start();

    }
}

class Data{
    private int number = 0;

    Lock lock = new ReentrantLock();
    //添加锁的监视器对象
    Condition condition = lock.newCondition();

    public void increament(){
        lock.lock();
        try{
            //业务代码
            while (number!= 0){
                //等待
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            //通知其他线程我+1完毕了
            condition.signalAll();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }

    public void decrement(){
        lock.lock();
        try{
            //业务代码
            while (number == 0){
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            //通知其他线程我减一完毕了
            condition.signalAll();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
}

Condtion 精准的通知和唤醒线程

package com.chen.pc;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/14 0:30
 * @Version V1.0
 **/

/***
 * A执完调用B
 * B执行完调用C
 * C执行完调用A
 */

public class ConditionLock {

    public static void main(String[] args) {

        Data3 data3 = new Data3();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printA();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printB();
            }
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printC();
            }
        },"C").start();
    }
}


class Data3{
    //资源类

    private Lock lock = new ReentrantLock();
    private Condition condition1 =lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();

    private int number = 1;

    public void printA(){
        lock.lock();
        try{
            //业务,判断，执行 通知
            while (number != 1){
                //等待
                condition1.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>AAAAAAAA");
            //唤醒指定的 人
            number = 2;
            condition2.signal();

        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }

    }

    public void printB(){

        lock.lock();
        try{
            //业务,判断，执行 通知
            while (number != 2){
                //等待
                condition2.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>BBBBBB");
            //唤醒指定的 人
            number = 3;
            condition3.signal();

        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }

    }

    public void printC(){

        lock.lock();
        try{
            //业务,判断，执行 通知
            while (number != 3){
                //等待
                condition3.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>CCCCCC");
            //唤醒指定的 人
            number = 1;
            condition1.signal();

        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }

    }

}

锁现象

锁的是谁！锁到底锁的是谁~

小结

new this 具体的一个收集

static Class 唯一的一个模板

集合类不安全

List不安全

package com.chen.unsafe;

import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/14 1:08
 * @Version V1.0
 **/
//并发修改异常
public class ListTest {
    public static void main(String[] args) {
//        List list = Arrays.asList("1","2","3");
//        list.forEach(System.out::println);

        /**
         * 1.List list = new Vector()
         * 2.  List list = Collections.synchronizedList(new ArrayList<>());
         * 3. List list = new CopyOnWriteArrayList<>();
         */
        //CopyOnWrite写入时 复制COW

        List<String> list = new CopyOnWriteArrayList<>();
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            },String.valueOf(i)).start();
        }

    }
}

set

package com.chen.unsafe;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 0:27
 * @Version V1.0
 **/

/**
 * 同理可证
 */

public class SetTest {
    public static void main(String[] args) {
//        Set set = new HashSet<>();
//        Set set = Collections.synchronizedSet(new HashSet<>());
        Set<String> set = new CopyOnWriteArraySet();

        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                set.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(set);
            },String.valueOf(i)).start();
        }
    }
}

HashMap 不安全

package com.chen.unsafe;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 0:38
 * @Version V1.0
 **/

public class MapTest {
    public static void main(String[] args) {
        //默认等价于什么
//        Map map = new HashMap(16, (float) 0.75);

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

        //加载因子，初始化容量
        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).toString()).start();

        }
    }
}

Callable(简单)

1. 可以有返回值
2. 可以抛出异常
3. 方法不同 run/call

package com.chen.callable;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 1:10
 * @Version V1.0
 **/

public class callableTest {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        new Thread().start();

        MyThread myThread = new MyThread();
        FutureTask futureTask = new FutureTask(myThread);   //适配器类

        new Thread(futureTask,"A").start();

        Integer o = (Integer)futureTask.get();//获取callable的返回结果

        System.out.println(o);
    }
}

class MyThread implements Callable<Integer> {

    @Override
    public Integer call() throws Exception {
        return 11;
    }
}

细节：

1. 有缓存
2. 结果可能需要等待,会阻塞!

常用的辅助类

CountDownLatchDemo

package com.chen.add;

import java.util.concurrent.CountDownLatch;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 13:53
 * @Version V1.0
 **/

public class CountDownLatchDemo {

    public static void main(String[] args) throws InterruptedException {
        //总数是6,必须要执行的任务的时候，再使用！
        CountDownLatch countDownLatch = new CountDownLatch(6);

        for (int i = 0; i < 6; i++) {
            new Thread(()->{
                System.out.println(Thread.currentThread().getName()+"Go out");
                countDownLatch.countDown();
            },String.valueOf(i).toString()).start();
        }

        //等待计数器归零，然后再向下执行
        countDownLatch.await();

        System.out.println("Close Door");

    }

}

原理：

• countDownLatch.countDown(); //数量减一
• countDownLatch.await();//等待计数器归零

每次有线程调用的时候countDown()数量减一，假设计数器变为0，countDownLatch.await();就会被唤醒,继续执行！

CyclicBarrier

package com.chen.add;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 14:01
 * @Version V1.0
 **/

public class CyclicBarrierDemo {
    public static void main(String[] args) {
        /**
         * 集齐7颗龙珠召唤神龙
         */

        //召唤龙珠的线程
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7,()->{
            System.out.println("召唤神龙成功!!");
        });




        for (int i = 0; i < 7; i++) {
            final int temp = i;
            new Thread(()->{
                //lambda能操作到i吗
                System.out.println(Thread.currentThread().getName()+" 收集"+ temp+"个龙珠");
                try {
                    cyclicBarrier.await();// 等待
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }

            }).start();
        }

    }
}

Semaphore

package com.chen.add;

import java.sql.Time;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 14:06
 * @Version V1.0
 **/

public class semaphoreDemo {

    public static void main(String[] args) {
        //线程数量: 停车位
        Semaphore semaphore = new Semaphore(3);

        for (int i = 0; i <= 6; i++) {
            new Thread(()->{
                // acquire()  得到
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName()+"抢到车位");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println(Thread.currentThread().getName()+"离开车位");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }finally {
                    //release()  释放
                    semaphore.release();
                }
            },String.valueOf(i)).start();
        }
    }
}

原理：

semaphore.acquire()获得，假设如果已经满了，等待，等待被释放~

semaphore.release() 释放，会将当前的信号量释放+1，然后唤醒等待的线程！

共享资源互斥的使用!并发限流，控制最大的线程数

读写锁

package com.chen.rw;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 14:16
 * @Version V1.0
 **/

/**
 *   独占锁 （写锁）   一次只能被一个线程占有
 *   共享锁   （读锁） 多个线程可以同时占有
 *  ReadWriteLock
 *  读-读 可以共存
 *  读-写 不能共存
 *  写-写 不能共存
 */

public class ReadWriteLockDemo {

    public static void main(String[] args) {
        MyCache myCache  = new MyCache();

        //写入
        for (int i = 0; i < 5; i++) {
            final  int temp = i;
            new Thread(()->{
                myCache.put(temp+"",temp+"");
            },String.valueOf(i)).start();
        }

        //读取
        for (int i = 0; i < 5; i++) {
            final  int temp = i;
            new Thread(()->{
                myCache.get(temp+"",temp+"");
            },String.valueOf(i)).start();
        }

    }

}

/**
 * 加锁的缓存
 */

class MyCacheLock{

    private volatile Map<String,Object> map = new HashMap<>();
    // 读写锁:更加细粒度的控制
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    //存   写入的时候，只希望有一个线程写
    public void put(String key,Object value){
        readWriteLock.writeLock().lock();
      try{
          System.out.println(Thread.currentThread().getName()+"写入"+key);
          map.put(key,value);
          System.out.println(Thread.currentThread().getName()+"写入ok");

      }catch (Exception e){
          e.printStackTrace();
      }finally {
          readWriteLock.writeLock().unlock();
      }
    }

    //取   读
    public void get(String key){

        readWriteLock.readLock().lock();

       try{
           System.out.println(Thread.currentThread().getName()+"读取"+key);
           Object o = map.get(key);
           System.out.println(Thread.currentThread().getName()+"读取ok");
       }catch (Exception e){
           e.printStackTrace();
       }finally {
           readWriteLock.readLock().unlock();
       }
    }
}




/**
 * 自定义缓存
 */
class MyCache{

    private volatile Map<String,Object> map = new HashMap<>();

    //存   写
    public void put(String key,Object value){
        System.out.println(Thread.currentThread().getName()+"写入"+key);
        map.put(key,value);
        System.out.println(Thread.currentThread().getName()+"写入ok");
    }

    //取   读
    public void get(String key){
        System.out.println(Thread.currentThread().getName()+"读取"+key);
        Object o = map.get(key);
        System.out.println(Thread.currentThread().getName()+"读取ok");
    }
}

阻塞队列

阻塞：

队列：

BlockingQueue：多线程并发处理，线程池!

学会使用队列：四组API

1. 抛出异常
2. 不会抛出异常
3. 阻塞 等待
4. 超时等待

方式	抛出异常	有返回值	阻塞 等待	超时等待
添加	add	offer	put	offer(,)
移除	remove	poll	take	poll(),
检测队首元素	element	peek

抛出异常

 /**
     * 抛出异常
     */
    public static void test1(){
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

       System.out.println( blockingQueue.add("a"));
        System.out.println( blockingQueue.add("b"));
        System.out.println( blockingQueue.add("c"));

        //队列慢了抛出异常:java.lang.IllegalStateException:Queue full
//        System.out.println( blockingQueue.add("d"));
        System.out.println("=========================================");

        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());

        //抛出异常：NoSuchElementException 
        System.out.println(blockingQueue.remove());

    }

有返回值没有异常

/**
     * 有返回值没有异常
     */
    public  static void test2(){
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue(3);

        System.out.println(arrayBlockingQueue.offer("a"));
        System.out.println(arrayBlockingQueue.offer("b"));
        System.out.println(arrayBlockingQueue.offer("c"));

//        System.out.println(arrayBlockingQueue.offer("d"));//false 不抛出异常

        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());

//        System.out.println(arrayBlockingQueue.poll());//null

    }

阻塞 等待

 /**
     * 等待，阻塞（一直
     */
    public static void test3() throws InterruptedException {
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue(3);

        //一直阻塞
        blockingQueue.put("a");
        blockingQueue.put("b");
        blockingQueue.put("c");
        //队列没有位置
//        blockingQueue.put("d");

        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());//没有这个元素

    }

阻塞 超时等待，实践限制

/**
     * 等待，阻塞（有计时
     */
    public static void test4() throws InterruptedException {
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue(3);

        blockingQueue.offer("a");
        blockingQueue.offer("b");
        blockingQueue.offer("c");
        blockingQueue.offer("d",2, TimeUnit.SECONDS);// 等待超过两秒就退出了

        System.out.println("=======================================");
        blockingQueue.poll();
        blockingQueue.poll();
        blockingQueue.poll();
        blockingQueue.poll(2,TimeUnit.SECONDS);

    }

线程池

池化技术

线程池的好处

1. 降低资源的消耗
2. 提高响应的速度
3. 方便管理

线程复用，可以控制最大的并发数，管理线程

线程池：三大方法，

package com.chen.pool;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 15:17
 * @Version V1.0
 **/
//使用线程池来创建线程
public class Demo01 {
    public static void main(String[] args) {
//        ExecutorService threadPool = Executors.newSingleThreadExecutor();// 单个线程
//        ExecutorService threadPool = Executors.newFixedThreadPool(5);//创建一个固定大小的线程池
        ExecutorService threadPool = Executors.newCachedThreadPool();//可伸缩的线程池

        //程序结束要关闭线程池
        try{
            for (int i = 0; i < 10; i++) {
                threadPool.execute(()->{
                    System.out.println(Thread.currentThread().getName()+"ok");
                });
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            threadPool.shutdown();
        }

    }
}

七大参数

public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }

 public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }

//本质是：ThreadPoolExecutor()
 
public ThreadPoolExecutor(int corePoolSize,		//核心线程池大小
                              int maximumPoolSize,//最大线程池大小
                              long keepAliveTime,//超时没有人调用就会释放
                              TimeUnit unit,//超时单位
                              BlockingQueue<Runnable> workQueue,//阻塞队列
                              ThreadFactory threadFactory,//线程工厂：创建线程，一般不用动
                              RejectedExecutionHandler handler) {//拒绝策略
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = (System.getSecurityManager() == null)
            ? null
            : AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

手动创建一个线程池

package com.chen.pool;

import java.util.concurrent.*;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 15:32
 * @Version V1.0
 **/

public class Demo02 {
    public static void main(String[] args) {
        //自定义线程。
        /**
         * 最大线程到底该如何定义
         * 1.CPU： 密集型，几核，就是几。可以保持CPU的效率最高
         * 2.IO 密集型->判断你的程序十分耗IO的线程
         *       程序: 15个大型任务,io 十分占用资源！
         */

        //获取CPU的核数
        System.out.println(Runtime.getRuntime().availableProcessors());

        ExecutorService threadPool = new ThreadPoolExecutor(2,5,3, TimeUnit.SECONDS,new LinkedBlockingDeque<>(3)
        , Executors.defaultThreadFactory(),new ThreadPoolExecutor.AbortPolicy());//可伸缩的线程池
        //最后一个参数的策略是，银行满了，还有人进来，就不处理这个人的，抛出异常

        //程序结束要关闭线程池
        try{
            for (int i = 1; i < 5; i++) {
                threadPool.execute(()->{
                    System.out.println(Thread.currentThread().getName()+"ok");
                });
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            threadPool.shutdown();
        }

    }
}

小结和扩展

池的最大的大小如何去设置!

了解：IO密集型，CPU密集型：（调优

四大函数式接口

代码测试：

函数式接口:

package com.chen.function;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 16:38
 * @Version V1.0
 **/

import java.util.function.Function;

/**
 * 函数型接口
 */

public class Demo01 {
    public static void main(String[] args) {
        //工具类：输出输入的值
//        Function function = new Function(){
//            @Override
//            public String apply(String o) {
//                return o;
//            }
//        };

        Function<String,String> function = (str) ->{return  str;};
        System.out.println(function.apply("hello"));
    }
}

断定型接口

package com.chen.function;

import java.util.function.Predicate;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 16:43
 * @Version V1.0
 **/

/**
 *  断定型接口:有一个输入参数，返回值只能是 布尔值！
 */
public class Demo02 {
    public static void main(String[] args) {
//        Predicate predicate = new Predicate() {
//            //判断字符串是否为空
//            @Override
//            public boolean test(String s) {
//                return s.isEmpty();
//            }
//        };

        Predicate<String> predicate = (str)->{ return str.isEmpty();};

        System.out.println(predicate.test("asd"));
    }
}

Consumer 消费型接口

package com.chen.function;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 16:49
 * @Version V1.0
 **/

import java.util.function.Consumer;

/**
 * Consumer 消费型接口：只有输入，目要返回值
 */
public class Demo03 {
    public static void main(String[] args) {
//        Consumer consumer = new Consumer(){
//            @Override
//            public void accept(String str) {
//                System.out.println(str);
//            }
//        };
        Consumer<String> consumer = (str) ->{System.out.println(str);};

        consumer.accept("hello");
    }
}

供给型接口

package com.chen.function;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 16:52
 * @Version V1.0
 **/

import java.util.function.Supplier;

/**
 * Supplier共给型接口，没有参数，只有返回值
 */
public class Demo04 {
    public static void main(String[] args) {
//        Supplier supplier = new Supplier() {
//            @Override
//            public Integer get() {
//              System.out.println("get()");
//              return 1024;
//            }
//        };

        Supplier supplier = ()->{return 1024;};
      System.out.println(supplier.get());
    }
}

要掌握的：泛型，枚举，反射；lambda表达式，链式表达式，函数式接口，Stream流式计算

Stream流式计算

大数据:存储+计算

计算都可以交给流来操作

package com.chen.stream;

import java.util.Arrays;
import java.util.List;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 17:31
 * @Version V1.0
 **/

/**
 * 题目要求：以分组内完成此题，只能用一行代码实现
 * 现有5个用户，筛选：
 * 1.ID必须是偶数
 * 2.年龄必须大于23岁
 * 3.用户名转换为大写字母
 * 4.用户名字母倒叙输出
 * 5.只能输出一个用户！
 */
public class Test {
    public static void main(String[] args) {
        User u1 = new User(1,"a",21);
        User u2 = new User(2,"b",22);
        User u3 = new User(3,"c",23);
        User u4 = new User(4,"d",24);
        User u5 = new User(6,"e",25);
        //集合就是存储
        List<User> list = Arrays.asList(u1,u2,u3,u4,u5);

        //计算交给流
        list.stream()
                .filter(u->{return u.getId()%2==0;})
                .filter(u->{return u.getAge()>23;})
                .map(u->{return u.getName().toUpperCase();})
                .sorted((uu1,uu2)->{return uu2.compareTo(uu1);})
                .limit(1)
                .forEach(System.out::println);
    }
}

ForkJoin

ForkJoin特点：工作窃取

ForkJoin

package com.chen.ForkJoin;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 17:47
 * @Version V1.0
 **/
//求和计算的任务
/**
 * 1. forkjoinPool  通过它来执行
 * 2. 计算任务 forkjoinPool.execute(ForkJoinTask tak)
 * 3. 计算类要继承 ForkJoinTask
 */

import java.util.concurrent.RecursiveTask;

/**
 * 如何使用forkjoin
 * 1.forkjoinpool 通过它来执行
 */
public class ForkJoinDemo extends RecursiveTask<Long> {

    private Long start;//1
    private Long end;//1990900000

    //零界值
    private Long temp = 10000L;

    public ForkJoinDemo(Long star,Long end){
        this.start = star;
        this.end = end;
    }

    public  void test() {
        if((end-start)>temp){
            //分支合并计算

        }else {
            int sum = 0;
            for (int i = 0; i < 10_0000_0000; i++) {
                sum += i;
            }
            System.out.println(sum);
        }
    }

    //计算的方法
    @Override
    protected Long compute() {
       if ((end-start)<temp){
           Long sum = 0L;
           for (Long i = start; i <= end; i++) {
                sum += i;
           }
           return sum;
       }else {//forkjoin 递归
            long middle = (start + end) / 2;// 中间值
           ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
           task1.fork();//拆分任务，把任务压入线程队列
           ForkJoinDemo task2 = new ForkJoinDemo(middle+1, end);
           task2.fork();//拆分任务，把任务压入线程队列
           return task1.join() + task2.join();
       }
    }
}

package com.chen.ForkJoin;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/15 18:57
 * @Version V1.0
 **/

public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
//        test1();//8952
//        test2();
//        test3();295
    }

    //普通程序员
    public static void test1(){
        long start = System.currentTimeMillis();
        Long sum = 0L;
        for(Long i = 1L;i<10_0000_0000;i++){
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sum="+"时间"+(end-start));
    }

    //会使用ForkJoin
    public static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();

        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinDemo task= new ForkJoinDemo(0L, 10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);
        Long summer = submit.get();

        long end = System.currentTimeMillis();
        System.out.println("sum="+"时间"+(end-start));
    }

    public static void test3(){
        long start = System.currentTimeMillis();

        //并行流Stream() ]
        LongStream.rangeClosed(0L,10_0000_0000L).parallel().reduce(0,Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("sum="+"时间"+(end-start));
    }
}

异步回调

Future 设计的初衷：对将未来的某个事情结果进行建模

package com.chen.future;

import java.util.concurrent.*;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 0:10
 * @Version V1.0
 **/

/**
 * 异步调用：CompletableFuture
 * 异步执行
 * 成功回调
 * 失败回调
 */

public class Demo01 {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //发起一个请求
        //没有返回值的异步回调
//        CompletableFuture objectCompletableFuture = CompletableFuture.runAsync(()->{
//            try {
//                TimeUnit.SECONDS.sleep(2);
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
//            System.out.println(Thread.currentThread().getName()+"runAsync=>Void");
//        });

//        objectCompletableFuture.get();// 获取阻塞执行结果
        //有返回值的异步回调
        //ajax 成功和失败的回调
        CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(()->{
            System.out.println(Thread.currentThread().getName()+"supplyAsnc=>Integer");
            return 1024;
        });

        completableFuture.whenComplete((t,u)->{
            System.out.println("t->"+t);//正常的返回结果
            System.out.println("u->"+u);//错误信息：
        }).exceptionally((e)->{
           System.out.println( e.getMessage());//可以获取到错误的结果
           return 233;
        });


    }
}

JMM

volatile 理解

Volatile 的java虚拟机的轻量级的同步机制

1. 保证可见性
2. 不保证原子性
3. 禁止指令重排

JMM what?

JMM:Java内存模型，不存在东西，概念！约定！

1. 线程解锁之前，必须把共享变量立刻刷回主存。
2. 线程加锁前，必须读取主存中的最新值到工作内存中！
3. 加锁和解锁是同一把锁

线程工作内存，主内存的八种操作:

贮存不可见出现的问题。

Volatile

程序不知道主内存中的值已经被修改过了

保证可见性

package com.chen.tvolatile;

import java.util.concurrent.TimeUnit;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 0:36
 * @Version V1.0
 **/

public class JMMDemo {
    //不加volatile程序就回死循环，因为程序不可见
    private volatile  static int num =0;
    public static void main(String[] args) {
        //主线程

        new Thread(()->{//线程1
            while (num == 0){

            }
        }).start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        num =1;
        System.out.println(num);

    }
}

不保证原子性

package com.chen.tvolatile;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 0:43
 * @Version V1.0
 **/

public class VDemo02 {

    //volatile 不保证原子性
    private volatile static int num = 0;

    public static void add(){
        num++;
    }

    public static void main(String[] args) {
        //理论上结果应该为2W
        for (int i = 0; i < 20; i++) {
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    add();
                }
            }).start();
        }

        while (Thread.activeCount()>2){
            Thread.yield();
        }
        System.out.println(Thread.currentThread().getName()+" "+num);
    }
}

指令重排

Volatile可以避免指令重排：

内存屏障，CPU指令。作用:

1. 保证特定的操作顺序
2. 可以保证某些变量的内存可见性(利用这些特性，就可以保持)

volatile 可以保证可见性，不能保证原子性,由于内存屏障，可以保证避免指令重排的现象产生!

单单单 单例模式

饿汉式

package com.chen.Single;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 1:03
 * @Version V1.0
 **/

public class Hungry {

    //耗费内存，还没使用就已经开始加载了
    private Hungry(){

    }

    private  final static Hungry HUNGRY = new Hungry();

    public static Hungry getInstance(){
        return HUNGRY;
    }

}

懒汉式

package com.chen.Single;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.TreeMap;
import java.util.function.Consumer;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 1:05
 * @Version V1.0
 **/
//懒汉式 单例
public class LazyMan {

    private static boolean flag = false;

    private LazyMan(){
      synchronized (LazyMan.class){
          if (flag == false){
              flag = true;
          }else {
              throw new RuntimeException("不要试图使用反射破坏异常");
          }
      }
    }

    private volatile static LazyMan lazyMan;

    //双重检测锁模式下 ，懒汉式单例模式 DCL懒汉式
    public static LazyMan getInstance(){
        if (lazyMan==null){
            synchronized (LazyMan.class){
                if (lazyMan==null){
                    lazyMan = new LazyMan();//不是一个原子性操作
                    /**
                     * 1.  分配内存空间
                     * 2.执行构造方法，初始化对象
                     * 3.把这个对象指向这个空间
                     */
                }
            }
        }
        return lazyMan;
    }

    // 单线程下是ok的
    public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
       LazyMan instance = LazyMan.getInstance();
        Constructor<LazyMan> declaredConstructor = LazyMan.class.getDeclaredConstructor();
        declaredConstructor.setAccessible(true);
        LazyMan instance2 = declaredConstructor.newInstance();

        System.out.println(instance);
        System.out.println(instance2);
    }

}

枚举实现

package com.chen.Single;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 1:19
 * @Version V1.0
 **/
//枚举
public enum EnumSingle {

    INSTANCE;

    public EnumSingle getInstance(){
        return INSTANCE;
    }
}

class Test{
    public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        EnumSingle instance1 = EnumSingle.INSTANCE;
        Constructor<EnumSingle> declaredConstructor = EnumSingle.class.getDeclaredConstructor(null);
        declaredConstructor.setAccessible(true);
        EnumSingle instance2 = declaredConstructor.newInstance();
        System.out.println(instance1);
        System.out.println(instance2);

    }
}

静态内部类

package com.chen.Single;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 1:11
 * @Version V1.0
 **/
//静态内部类
public class Holder {
    private Holder(){

    }

    public static Holder getInstance(){
        return InnerClass.holder;
    }

    public static class InnerClass{
        private static final Holder holder = new Holder();
    }
}

理解CAS

什么是CAS

package com.chen.cas;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 1:29
 * @Version V1.0
 **/

public class CASDemo {

    AtomicInteger atomicInteger = new AtomicInteger(2020);

    //CAS  compareAndSet：比较并交换!
    public static void main(String[] args) {
        AtomicInteger atomicInteger = new AtomicInteger(2020);

        //如果我期望的值达到了就更新，否则就不更新  CAS 是CPU的并发原语！
        System.out.println(atomicInteger.compareAndSet(2020, 2021));
        System.out.println(atomicInteger.get());

        atomicInteger.getAndIncrement();

        System.out.println(atomicInteger.compareAndSet(2020, 2021));
        System.out.println(atomicInteger.get());

    }
}

CAS：比较当前工作内存中的值，如果这个值是期望的，那么则执行操作！如果不是就一直循环！

缺点：

1. 自旋锁循环耗时
2. 一次性只能保证一个共享变量的原子性
3. 存在ABD问题

Unsafe类

ABA 问题

package com.chen.cas;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 1:29
 * @Version V1.0
 **/

public class CASDemo {

    AtomicInteger atomicInteger = new AtomicInteger(2020);

    //CAS  compareAndSet：比较并交换!
    public static void main(String[] args) {
        AtomicInteger atomicInteger = new AtomicInteger(2020);

        //对于我们平时写的sql：乐观锁!
        //如果我期望的值达到了就更新，否则就不更新  CAS 是CPU的并发原语！
        System.out.println("========捣乱的线程=======================");
        System.out.println(atomicInteger.compareAndSet(2020, 2021));
        System.out.println(atomicInteger.get());

        System.out.println(atomicInteger.compareAndSet(2021, 2020));
        System.out.println(atomicInteger.get());

        System.out.println("===========================================");
        System.out.println(atomicInteger.compareAndSet(2020, 2021));
        System.out.println(atomicInteger.get());

    }
}

各种锁的理解

1.公平锁，非公平锁

公平锁:非常公平，不能够插队，必须先来后到

非公平锁：非常不公平，可以插队(默认都是非公平的)

public ReentrantLock() {
        sync = new NonfairSync();
    }

public ReentrantLock(boolean fair) {
        sync = fair ? new FairSync() : new NonfairSync();
    }

2. 可重入锁

可重入锁(递归锁)

Synchronized

package com.chen.lock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 2:02
 * @Version V1.0
 **/
//Synchronized
public class Demo01 {
    public static void main(String[] args) {
        Phone phone = new Phone();

        new Thread(()->{
            phone.ms();
        },"A").start();

        new Thread(()->{
            phone.ms();
        },"B").start();
    }
}

class Phone{
    public synchronized void ms(){
        System.out.println(Thread.currentThread().getName()+"sms");
        call();// 这里也有锁
    }

    public synchronized void call(){
        System.out.println(Thread.currentThread().getName()+"call");
    }
}

Lock

package com.chen.lock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 2:06
 * @Version V1.0
 **/

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 2:02
 * @Version V1.0
 **/
//Synchronized
public class Demo02 {
    public static void main(String[] args) {
        Phone2 phone = new Phone2();

        new Thread(()->{
            phone.ms();
        },"A").start();

        new Thread(()->{
            phone.ms();
        },"B").start();
    }
}

class Phone2{

    Lock lock = new ReentrantLock();

    public  void ms(){
        lock.lock();
        try{
            System.out.println(Thread.currentThread().getName()+"sms");
            call();// 这里也有锁
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }

    public  void call(){
        //锁必须配对
        lock.lock();
        try{
            System.out.println(Thread.currentThread().getName()+"call");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
}

自旋锁

spinLock

package com.chen.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 2:15
 * @Version V1.0
 **/

public class TestSpinLock {
    public static void main(String[] args) throws InterruptedException {
        ReentrantLock reentrantLock = new ReentrantLock();
        reentrantLock.lock();
        reentrantLock.unlock();

        // 底层使用自旋锁实现的
        SpinlockDemo lock = new SpinlockDemo();

        new Thread(()->{
            lock.myLock();
            try{
                TimeUnit.SECONDS.sleep(3);
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                lock.myUnLock();
            }
        },"T1").start();


        TimeUnit.SECONDS.sleep(1);

        new Thread(()->{
            lock.myLock();
            try{
                TimeUnit.SECONDS.sleep(1);
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                lock.myUnLock();
            }
        },"T2").start();
    }
}

死锁

package com.chen.lock;

import java.util.concurrent.TimeUnit;

/**
 * @Author 晨边#CB
 * @Date:created in  2020/5/16 2:21
 * @Version V1.0
 **/

public class DeadLockDemo {
    public static void main(String[] args) {

        String lockA = "lockA";
        String lockB = "lockB";

        new Thread(new MyThread(lockA,lockB),"T1").start();
        new Thread(new MyThread(lockB,lockA),"T2").start();
    }
}

class MyThread implements Runnable{

    private String lockA;
    private String lockB;

    public MyThread(String lockA,String lockB){
        this.lockA = lockA ;
        this.lockB = lockB;
    }

    @Override
    public void run() {
        synchronized (lockA){
            System.out.println(Thread.currentThread().getName()+"lock："+lockA+"=>get"+lockB);

            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (lockB){
                System.out.println(Thread.currentThread().getName()+"lock："+lockB+"=>get"+lockA);
            }
        }
    }

    private String
}

解决问题

1. 使用jps定位进程号

2. 使用jstack进程号查看进行信息

暑期在中国科学院软件应用技术研究所学习的内容。
之前用Typora写了之后上传到GitHub
现在搬运过来csdn了