并发编程juc

该笔记大部分搬运B站遇见狂神说的javaJUC，顺便把图文合并记录，便于回顾

视频地址：【狂神说Java】JUC并发编程最新版通俗易懂_哔哩哔哩_bilibili记得三连

目录

1.什么是JUC?

2.线程进程和程序

3.Lock锁(重点)

4.生产者和消费者问题!

5.八锁现象

6.集合安全问题

7.Callable (简单)

8.常用辅助类（必会）

9.读写锁

10.阻塞队列

11.线程池(重点)

12.四大函数式接口(必须掌握)

13.Stream流式计算

14.ForkJoin

15.异步回调

16.JMM

1.什么是JUC?

JUC是指javaUtil包中的三个操作线程的包!

2.线程进程和程序

程序(Program):是一个静态的概念，一般对应于操作系统中的一个可执行的文件

，比如：我们要启动酷狗听音乐，则对应酷狗可执行程序。当我们双击酷狗，则加载

程序到内存中，开始执行该程序，于是产生了"进程".

进程:执行中的程序叫做进程(Process),是一个动态的概念。现代的操作系统都可以同时启动多个进程。比如:我们在用酷狗听音乐，也可以使用wps写文档，也可以同时用浏览器查看网页。可以通过任务管理器查看当前的进程.

线程:是进程的一个执行路径，一个进程中至少有一个线程，进程中的多个线程共享进程的资源。

java默认有两个线程:main(主)现场和GC(垃圾回收)线程

提问:java真的可以开启线程吗?开启不了!

    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 */
            }
        }
    }
        //这是一个C++底层，Java是没有权限操作底层硬件的
    private native void start0();

Java是没有权限去开启线程、操作硬件的，这是一个native的一个本地方法，它调用的底层的C++代码。

并发、并行

并发： 多线程操作同一个资源。

• CPU 只有一核，模拟出来多条线程，天下武功，唯快不破。那么我们就可以使用CPU快速交替，来模拟多线程。

并行： 多个人(CPU内核)一起行走(运行)

• CPU多核，多个线程可以同时执行。 我们可以使用线程池！

public class Test1 {
    public static void main(String[] args) {
        //获取cpu的核数
        System.out.println(Runtime.getRuntime().availableProcessors());
    }
}

并发编程的本质：充分利用CPU的资源！

线程有几个状态？

线程的状态：6个状态

public enum State {
        /**
         * Thread state for a thread which has not yet started.
         */
        //运行(新生,就绪)
        NEW,

        /**
         * Thread state for a runnable thread.  A thread in the runnable
         * state is executing in the Java virtual machine but it may
         * be waiting for other resources from the operating system
         * such as processor.
         */
        //运行
        RUNNABLE,

        /**
         * Thread state for a thread blocked waiting for a monitor lock.
         * A thread in the blocked state is waiting for a monitor lock
         * to enter a synchronized block/method or
         * reenter a synchronized block/method after calling
         * {@link Object#wait() Object.wait}.
         */
        //阻塞
        BLOCKED,

        /**
         * Thread state for a waiting thread.
         * A thread is in the waiting state due to calling one of the
         * following methods:
         * <ul>
         *   <li>{@link Object#wait() Object.wait} with no timeout</li>
         *   <li>{@link #join() Thread.join} with no timeout</li>
         *   <li>{@link LockSupport#park() LockSupport.park}</li>
         * </ul>
         *
         * <p>A thread in the waiting state is waiting for another thread to
         * perform a particular action.
         *
         * For example, a thread that has called <tt>Object.wait()</tt>
         * on an object is waiting for another thread to call
         * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
         * that object. A thread that has called <tt>Thread.join()</tt>
         * is waiting for a specified thread to terminate.
         */
        //等待
        WAITING,

        /**
         * Thread state for a waiting thread with a specified waiting time.
         * A thread is in the timed waiting state due to calling one of
         * the following methods with a specified positive waiting time:
         * <ul>
         *   <li>{@link #sleep Thread.sleep}</li>
         *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
         *   <li>{@link #join(long) Thread.join} with timeout</li>
         *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
         *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
         * </ul>
         */
        //超时等待
        TIMED_WAITING,

        /**
         * Thread state for a terminated thread.
         * The thread has completed execution.
         */
        //终止
        TERMINATED;
    }

wait/sleep的区别？

1、来自不同的类

wait => Object

sleep => Thread

一般情况企业中使用休眠是：

TimeUnit.DAYS.sleep(1); //休眠1天
TimeUnit.SECONDS.sleep(1); //休眠1s

2、关于锁的释放

wait 释放锁睡；

sleep 抱着锁睡；

3、使用的范围是不同的

wait 必须在同步代码块中；

sleep 可以在任何地方睡；

4、是否需要捕获异常

wait是不需要捕获异常(中断异常除外,所有线程都有中断异常)；

sleep必须要捕获异常；

3.Lock锁(重点)

传统:synchronized

package com.test.demo;

/**
 * 基本的卖票例子
 * 记住:线程就是一个单独的资源类,没用任何的附属操作！
 */
public class Demo01{
    public static void main(String[] args) {
        //多线程操作
        Ticket ticket = new Ticket();

        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"A").start();
        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"B").start();
        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"C").start();
        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"D").start();
    }
}

//资源类
class Ticket{
    private static int number=50;

    //卖票方式
    public synchronized void sale(){
        if (number>0){
            System.out.println(Thread.currentThread().getName() + "购买了第" + (number--) + "张票,剩余票数为"+number);
        }
    }
}

Lock接口

公平锁:十分公平，必须先来后到~

非公平锁:十分不公平,可以插队(默认为非公平锁).

package com.test.demo;

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

/**
 * 基本的卖票例子
 * 记住:线程就是一个单独的资源类,没用任何的附属操作！
 */
public class Demo01{
    public static void main(String[] args) {
        //多线程操作
        Ticket ticket = new Ticket();

        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"A").start();
        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"B").start();
        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"C").start();
        new Thread(()-> { for (int i = 0; i < 60; i++) ticket.sale(); },"D").start();
    }
}

//资源类
class Ticket{
    private static int number=50;

    Lock lock= new ReentrantLock();

    //卖票方式
    public void sale(){
        //加锁
        lock.lock();
        try {
            if (number>0){
                System.out.println(Thread.currentThread().getName() + "购买了第" + (number--) + "张票,剩余票数为"+number);
            }
        } finally {
            //解锁
            lock.unlock();
        }
    }
}

synchronized锁与Lock锁的区别

1. synchronized是内置的java关键字而Lock是一个接口
2. synchronized无法判断获取锁的状态,Lock可以判断是否获取到了锁
3. synchronized会自动释放锁,Lock必须要手动释放锁！否则会造成死锁.
4. synchronized 线程1(获得锁,阻塞),线程2(等待,傻傻的等);Lock锁就不会一直等下去
5. synchronized 可重入锁 不可以中断的 非公平,Lock 可重入锁 可以判断的 非公平(可以设置)
6. synchronized 适合锁少量同步代码,Lock适合锁大量同步代码.

锁是什么?如何判断锁的是谁?

个人理解:锁是一种用于解决安全的机制,java中锁一般都是锁的对象,或者锁的是需要进行增删改的属性或发方法.

4.生产者和消费者问题!

synchronized版

package JUC.PC;

public class A {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(()->{
            try {
                for (int i = 0; i < 20; i++) {
                    data.Production();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"A").start();

        new Thread(()->{
            try {
                for (int i = 0; i < 20; i++) {
                    data.Consumption();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"B").start();
    }
}

//资源类
class Data {
    private int number = 0;

    //生产
    public synchronized void Production() throws InterruptedException {
        if (number != 0) {
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName()+"线程生产+1，目前总数"+number);
        this.notifyAll();
    }

    //消费
    public synchronized void Consumption() throws InterruptedException {
        if (number==0){
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName()+"线程消费-1，目前总数"+number);
        this.notifyAll();
    }
}

如果有ABCD4个线程则会出现问题！虚假唤醒！

解决方案:将if改为while即可

package JUC.PC;

public class A {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Production();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Consumption();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "B").start();

        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Production();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "C").start();

        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Consumption();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "D").start();

    }
}

//资源类
class Data {
    private int number = 0;

    //生产
    public synchronized void Production() throws InterruptedException {
        while (number != 0) {
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName() + "线程生产+1，目前总数" + number);
        this.notifyAll();
    }

    //消费
    public synchronized void Consumption() throws InterruptedException {
        while (number == 0) {
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName() + "线程消费-1，目前总数" + number);
        this.notifyAll();
    }
}

JUC版的生产者和消费者问题

package JUC.PC;

import java.lang.management.LockInfo;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class A {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Production();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Consumption();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "B").start();

        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Production();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "C").start();

        new Thread(() -> {
            try {
                for (int i = 0; i < 20; i++) {
                    data.Consumption();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "D").start();

    }
}

//资源类
class Data {
    private int number = 0;

    Lock reentrantLock = new ReentrantLock();
    Condition condition = reentrantLock.newCondition();

    //生产
    public void Production() throws InterruptedException {
        try {
            reentrantLock.lock();
            while (number != 0) {
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName() + "线程生产+1，目前总数" + number);
            condition.signalAll();
        } finally {
            reentrantLock.unlock();
        }
    }

    //消费
    public void Consumption() throws InterruptedException {
        try {
            reentrantLock.lock();
            while (number == 0) {
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName() + "线程消费-1，目前总数" + number);
            condition.signalAll();
        } finally {
            reentrantLock.unlock();
        }

    }
}

任何一个新技术,绝不仅仅只是覆盖了原来的技术,一定有它的优势和补充了原来的技术！

Condition 精准通知和唤醒线程

可以定义多个监视器进行精准通知如:

package JUC.PC;

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

public class B {
    public static void main(String[] args) {
        Data01 data01 = new Data01();
        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                data01.printA();
            }
        }, "A").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                data01.printB();
            }
        }, "B").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                data01.printC();
            }
        }, "C").start();


        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                data01.printD();
            }
        }, "D").start();
    }
}

class Data01 {
    //可重入锁
    private final Lock lock = new ReentrantLock();
    //监视器
    private final Condition condition1 = lock.newCondition();
    private final Condition condition2 = lock.newCondition();
    private final Condition condition3 = lock.newCondition();
    private final Condition condition4 = lock.newCondition();
    //物品数量
    private int count = 0;

    //生产
    public void printA() {
        lock.lock();
        try {
            while (count != 0) {
                //等待
                condition1.await();
            }
            count++;
            System.out.println(Thread.currentThread().getName() + "生产物品数量+1物品还剩" + count + "个,通知B消费");
            //唤醒B
            condition2.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

    //消费
    public void printB() {
        lock.lock();
        try {
            while (count <= 0) {
                condition2.await();
            }
            count--;
            System.out.println(Thread.currentThread().getName() + "消费物品数量-1物品还剩" + count + "个，通知C生产");
            //通知C
            condition3.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    //生产
    public void printC() {
        try {
            lock.lock();
            while (count != 0) {
                //等待
                condition3.await();
            }
            count++;
            System.out.println(Thread.currentThread().getName() + "生产物品数量+1物品还剩" + count + "个,通知D消费");
            //唤醒D
            condition4.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    //消费
    public void printD() {
        lock.lock();
        try {
            while (count <= 0) {
                condition4.await();
            }
            count--;
            System.out.println(Thread.currentThread().getName() + "消费物品数量-1物品还剩" + count + "个，通知A生产");
            //通知A
            condition1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

5.八锁现象

如何判断锁的是什么?

锁对象或class对象!

问题1:在标准情况下，两个线程是先发短信还是先打电话?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 1.在标准情况下，两个线程是先发短信还是先打电话?    先发短信
 */
public class Test1 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> {
            phone.sendSms();
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

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

class Phone {
    //发短信
    public synchronized void sendSms()  {
        System.out.println("发短信中...");
    }

    //打电话
    public synchronized void call() {
        System.out.println("打电话中...");
    }
}

问题2:在sendSms方法延迟了4秒后的情况下，两个线程是先发短信还是先打电话?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 1.在标准情况下，两个线程是先发短信还是先打电话?    先发短信
 * 2.在sendSms方法延迟了4秒后的情况下，两个线程是先发短信还是先打电话?    先发短信，因为两个方法都是同一个对象所以代表着谁先拿到锁谁就先执行
 */
public class Test1 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> {
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

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

class Phone {
    //发短信 
    public synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信中...");
    }

    //打电话
    public synchronized void call() {
        System.out.println("打电话中...");
    }
    
}

问题3:这里输出发短信还是hello?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 1.在标准情况下，两个线程是先发短信还是先打电话?    先发短信
 * 2.在sendSms方法延迟了4秒后的情况下，两个线程是先发短信还是先打电话?    先发短信，因为两个方法都是同一个对象所以代表着谁先拿到锁谁就先执行
 * 3.这里输出发短信还是hello?    hello 因为着hello这个方法并没有上锁，且发短信的方法以及拉到了锁但是需要睡眠4秒所以是hello
 */
public class Test1 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> {
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

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

class Phone {
    //发短信
    public synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信中...");
    }

    //打电话
    public synchronized void call() {
        System.out.println("打电话中...");
    }

    public void hello(){
        System.out.println("hello");
    }
}

问题四:有两个对象先执行发短信还是打电话?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 1.在标准情况下，两个线程是先发短信还是先打电话?    先发短信
 * 2.在sendSms方法延迟了4秒后的情况下，两个线程是先发短信还是先打电话?    先发短信，因为两个方法都是同一个对象所以代表着谁先拿到锁谁就先执行
 * 3.这里输出发短信还是hello?    hello 因为着hello这个方法并没有上锁，且发短信的方法以及拉到了锁但是需要睡眠4秒所以是hello
 * 4.有两个对象先执行发短信还是打电话? 打电话,应为这里有了两个对象将不在受锁的影响,而sendSms方法中又睡眠的4秒所以是先打电话
 */
public class Test1 {
    public static void main(String[] args) throws InterruptedException {
        //两个对象
        Phone phone = new Phone();
        Phone phone01 = new Phone();
        new Thread(() -> {
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

        new Thread(() -> {
            phone01.call();
        }, "B").start();
    }
}

class Phone {
    //发短信
    public synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信中...");
    }

    //打电话
    public synchronized void call() {
        System.out.println("打电话中...");
    }
}

5.增加两个静态同步方法，只有一个对象，先发短信还是先打电话?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 5.增加两个静态同步方法，只有一个对象，先发短信还是先打电话? 发短信,因为静态的方法从属于类则锁锁的就是类了,而sendSms短信是最先拿到锁的
 */
public class Test2 {
    public static void main(String[] args) throws InterruptedException {
        //两个对象
        Phone phone = new Phone();
        new Thread(() -> {
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

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

class Phone {
    //发短信
    public static synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信中...");
    }

    //打电话
    public static synchronized void call() {
        System.out.println("打电话中...");
    }
}

6.增加两个静态同步方法，两个个对象，先发短信还是先打电话?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 6.增加两个静态同步方法，两个个对象，先发短信还是先打电话? 发短信,因为静态的方法从属于类则锁锁的就是类了,而sendSms短信是最先拿到锁的
 */
public class Test3 {
    public static void main(String[] args) throws InterruptedException {
        //两个对象
        Phone phone = new Phone();
        Phone phone02 = new Phone();

        new Thread(() -> {
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

        new Thread(() -> {
            phone02.call();
        }, "B").start();
    }
}

class Phone {
    //发短信
    public static synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信中...");
    }

    //打电话
    public static synchronized void call() {
        System.out.println("打电话中...");
    }
}

7.一个静态同步方法,一个非静态同步方法，只有一个对象，先发短信还是先打电话?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 7.一个静态同步方法,一个非静态同步方法，只有一个对象，先发短信还是先打电话? 打电话,因为一个锁的是class一个锁的是对象,但是发短信会延迟4秒而打电话只延迟一秒所以是打电话.
 */
public class Test4 {
    public static void main(String[] args) throws InterruptedException {
        //两个对象
        Phone phone = new Phone();

        new Thread(() -> {
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

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

class Phone {
    //发短信
    public static synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信中...");
    }

    //打电话
    public synchronized void call() {
        System.out.println("打电话中...");
    }
}

8. 一个静态同步方法,一个非静态同步方法，两个对象，先发短信还是先打电话?

package JUC.Lock8;

import java.util.concurrent.TimeUnit;

/**
 * 8锁，就是关于锁的八个问题
 * 8.一个静态同步方法,一个非静态同步方法，两个对象，先发短信还是先打电话? 打电话,因为一个锁的是class一个锁的是对象,但是发短信会延迟4秒而打电话只延迟一秒所以是打电话.
 */
public class Test4 {
    public static void main(String[] args) throws InterruptedException {
        //两个对象
        Phone phone = new Phone();
        Phone phone02 = new Phone();
        new Thread(() -> {
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);

        new Thread(() -> {
            phone02.call();
        }, "B").start();
    }
}

class Phone {
    //发短信
    public static synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信中...");
    }

    //打电话
    public synchronized void call() {
        System.out.println("打电话中...");
    }
}

小结：

• 如果是非静态的synchronized是锁的调用它的对象!
• 如果为静态的synchronized是锁的是Class类模板!

6.集合安全问题

List

当在单线程中List是安全的,但在并发中ArrayList是不安全的如:

package JUC.List;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

public class TestList {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        for (int i = 1; i <= 100; i++) {
            new Thread(()->{
                list.add(UUID.randomUUID().toString().substring(0, 10));
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

就会出现了:ConcurrentModificationException(并发修改异常),解决方案:

• 使用synchronized给ArrayList的add方法加锁(ArrayList是1.2出来的)
• 使用List的子类Vector集合类着里面加入了synchronized(Vector是1.0出来的)
• 使用Collections.synchronizedList()方法将集合转换为安全的集合
• 使用CopyOnWriteArrayList类在java并发包concurrent下！

这里推荐使用CopyOnWriteArrayList因为:

• 不同于Vector，它并不是锁的对象,而是锁了进行修改的数组,提高了效率
• 它的add方法对传入的数据进行了Copy然后才进行保存，提高了安全。

package JUC.List;

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

public class TestList {
    public static void main(String[] args) {
        List<String> list = new CopyOnWriteArrayList<>();
        for (int i = 1; i <= 100; i++) {
            new Thread(()->{
                list.add(UUID.randomUUID().toString().substring(0, 10));
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

Set

package JUC.List;

import java.util.*;

//同理可得:ConcurrentModificationException(并发修改异常)
public class TestList {
    public static void main(String[] args) {
        Set<String> set = new HashSet<>();
        for (int i = 1; i <= 100; i++) {
            new Thread(()->{
                set.add(UUID.randomUUID().toString().substring(0, 10));
                System.out.println(set);
            },String.valueOf(i)).start();
        }
    }
}

解决方案:

• 使用Collections.synchronizedSet()方法将集合转换为安全的set集合！
• 使用ConcurrentSkipListSet类在java并发包concurrent下!

HashSet的底层就是使用了HashMap的键去存储的！同理ConcurrentSkipListSet类的底层是使用了ConcurrentSkipListMap的键进行存储！

Map

面试题:

Map是这样用的吗?

HashMap<Object, Object> objectObjectHashMap = new HashMap<>();

默认等价什么?

默认的容量为16默认的加载因子是0.75

同时HashMap也是不安全的

package JUC.List;

import java.util.HashMap;
import java.util.UUID;

//同理会报:ConcurrentModificationException(并发修改异常)
public class TestMap {
    public static void main(String[] args) {
        HashMap<Object, Object> hashMap = new HashMap<>();
        for (int i = 0; i < 100; i++) {
            new Thread(()->{
                hashMap.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0, 10));
                System.out.println(hashMap);
            }).start();
        }
    }
}

解决方案:

• 使用Collections.synchronizedSortedMap()把Map转换为安全的集合
• 使用ConcurrentHashMap类在java并发包concurrent下!

7.Callable (简单)

Callable多线程的第三种实现方式:

1. 表示有返回值
2. 可以抛出异常
3. 方法不同，run()/call()

而这样如何去调用Thread进行启动Callable线程了?

这里就有一个实现了Runnable的类叫做FutureTask类(适配器模式),它去实现了Runnable接口可以通过它去进行调用Thread.

如:

package JUC.Callable;

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

public class TestCallable {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //创建适配器
        FutureTask<Integer> futureTask = new FutureTask<>(new MyCallable());
        //因为FutureTask实现了RunnableFuture接口所以可以通过Thread启动线程
        new Thread(futureTask,"A").start();
        //获取线程返回值
        System.out.println(futureTask.get());
    }
}

class MyCallable implements Callable<Integer> {

    /**
     * Computes a result, or throws an exception if unable to do so.
     *
     * @return computed result
     * @throws Exception if unable to compute a result
     */
    @Override
    public Integer call() throws Exception {
        System.out.println("你好");
        return 1024;
    }
}

细节问题:

• 有缓存!
• 接口可能会遭到堵塞,需要等待线程执行完毕！

8.常用辅助类（必会）

CountDownLatch类:

该类可以用作一个减法计数器去执行实例:

package JUC.AuxiliaryClass;

import java.util.concurrent.CountDownLatch;

//计数器
public class TestCountDownLatch {
    public static void main(String[] args) throws InterruptedException {
        //总数是6
        CountDownLatch countDownLatch = new CountDownLatch(6);
        for (int i = 0; i < 6; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName()+"走了");
                countDownLatch.countDown();//表示数量-1
            },String.valueOf(i)).start();
        }
        //等待计数器归零在往下执行!
        countDownLatch.await();

        System.out.println("关门!");
    }
}

常用方法:

• countDownLatch.countDown();//表示数量-1
• countDownLatch.await(); //等待计数器归零在往下执行!

原理:当每次有线程调用 countDown()方法则数量减一,假设数量变为0，await()方法就会被唤醒继续执行！

CyclicBarrier类

加法计数器:

package JUC.AuxiliaryClass;

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

public class TestSemaphore {
    public static void main(String[] args) {
        //线程数量,停车位,限流的时候会用
        Semaphore semaphore = new Semaphore(3);
        for (int i = 0; i < 8; i++) {
            new Thread(()->{
                //acquire() 得到
                //release() 释放
                try {
                    //得到车位
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName()+"得到车位!");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println(Thread.currentThread().getName()+"停车两秒后离开车位!");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }finally {
                    //离开车位
                    semaphore.release();
                }
            }).start();
        }
    }
}

Semaphore类

实例:

package JUC.AuxiliaryClass;

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

public class TestSemaphore {
    public static void main(String[] args) {
        //线程数量,停车位,限流的时候会用
        Semaphore semaphore = new Semaphore(3);
        for (int i = 0; i < 8; i++) {
            new Thread(()->{
                //acquire() 得到
                //release() 释放
                try {
                    //得到车位
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName()+"得到车位!");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println(Thread.currentThread().getName()+"停车两秒后离开车位!");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }finally {
                    //离开车位
                    semaphore.release();
                }
            }).start();
        }
    }
}

常用方法:

• semaphore.acquire(); //获得
• semaphore.release(); //释放

原理:使用acquire()方法获取一个资源,如果没有则等待,release()释放资源则资源+1.

作用:多个共享资源的互斥使用！并发限流,控制最大线程数！

9.读写锁

ReadWriteLock

ReadWriteLock叫做读写锁是java.util.concurrent.locks包下的,它的写锁可以进行一次只被一个线程共享的操作,读锁则可以被所有线程共享,锁已又称为，独占锁(写锁)和共享锁(读锁)，如:

package JUC.Lock;

import java.util.HashMap;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * 小结:
 * 独占锁(写锁):一次只能被一个线程占用
 * 共享锁(读锁):多线程可以同时占有
 * 读-读:可以共存!
 * 读-写:不能共存!
 * 写-写:不能共存!
 */
public class TestReadWriteLock {
    public static void main(String[] args) {
        MyCacheLock myCache = new MyCacheLock();
        //存写的线程
        for (int i = 0; i < 5; i++) {
            int temp=i;
            new Thread(()->{
                myCache .put(String.valueOf(temp),temp);
            },String.valueOf(i)).start();
        }

        //读写的线程
        for (int i = 0; i < 5; i++) {
            int temp=i;
            new Thread(()->{
                myCache.get(String.valueOf(temp));
            },String.valueOf(i)).start();
        }
    }
}

/**
 * 自定义缓存
 */
class MyCache{
    private volatile HashMap<String,Object> map=new HashMap<>();

    //存写
    public void put(String key,Object value){
        System.out.println(Thread.currentThread().getName()+"正在写入"+key+":"+value);
        map.put(key,value);
        System.out.println(Thread.currentThread().getName()+"写入完毕");
    }

    //读取
    public void get(String key){
        System.out.println(Thread.currentThread().getName()+"正在读取"+key);
        Object o = map.get(key);
        System.out.println(Thread.currentThread().getName()+"读取完毕");
    }
}


/**
 * 加锁的自定义缓存
 */
class MyCacheLock{
    private volatile HashMap<String,Object> map=new HashMap<>();
    //读写锁,更加细腻度的控制
    private final ReentrantReadWriteLock lock=new ReentrantReadWriteLock();

    //存写 (存写的时候只希望有一个线程进行)
    public void put(String key,Object value){
        //上一把写锁
        lock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"正在写入"+key+":"+value);
            map.put(key,value);
            System.out.println(Thread.currentThread().getName()+"写入完毕");
        } finally {
            lock.writeLock().unlock();
        }
    }

    //读取 (所有人都可以读)
    public void get(String key){
        lock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"正在读取"+key);
            Object o = map.get(key);
            System.out.println(Thread.currentThread().getName()+"读取完毕");
        } finally {
            lock.readLock().unlock();
        }
    }
}

10.阻塞队列

BlockingQueue不是新的东西同它的老祖宗也继承了Collection接口(同时也继承了Queue队列接口))

什么情况下会使用堵塞队列?

• 多线程并发处理
• 线程池！

使用队列

四组API:

    //会抛出异常
    public static void test1(){
        ArrayBlockingQueue<Object> objects = new ArrayBlockingQueue<>(3);
        System.out.println(objects.add("a"));
        System.out.println(objects.add("b"));
        System.out.println(objects.add("c"));
        //IllegalStateException: Queue full(队列已满异常!)
        //System.out.println(objects.add("d"));

        System.out.println("===================");

        System.out.println(objects.remove());
        System.out.println(objects.remove());
        System.out.println(objects.remove());
        //NoSuchElementException(队列为空异常!)
        //System.out.println(objects.remove());
    }

    //有返回值.不抛出异常
    public static void test2(){
        ArrayBlockingQueue<Object> objects = new ArrayBlockingQueue<>(3);
        System.out.println(objects.offer("a"));
        System.out.println(objects.offer("b"));
        System.out.println(objects.offer("c"));
        System.out.println(objects.offer("d"));//false
        System.out.println("===================");
        System.out.println(objects.poll());
        System.out.println(objects.poll());
        System.out.println(objects.poll());
        System.out.println(objects.poll());//null
    }

    //等待,阻塞(一直阻塞)
    public static void test3() throws InterruptedException {
        ArrayBlockingQueue<Object> arrayBlockingQueue = new ArrayBlockingQueue<>(3);
        arrayBlockingQueue.put("a");
        arrayBlockingQueue.put("b");
        arrayBlockingQueue.put("c");
        //arrayBlockingQueue.put("d");//队列没有位置了则会等待

        System.out.println(arrayBlockingQueue.take());
        System.out.println(arrayBlockingQueue.take());
        System.out.println(arrayBlockingQueue.take());
        //System.out.println(arrayBlockingQueue.take()); //队列没有元素了则会等待
    }

    //超时等待
    public static void test4() throws InterruptedException {
        ArrayBlockingQueue<Object> 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", 2, TimeUnit.SECONDS));//等待超过两秒就退出
        System.out.println("===================");
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll(2, TimeUnit.SECONDS));//等待超过两秒就退出
    }

SynchronousQueue(同步队列)

没有容量,当进去一个元素必须等待取出才能再次进入元素！

package JUC.Queue;

import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;

public class TestSynchronousQueue {
    public static void main(String[] args) throws InterruptedException {
        SynchronousQueue<Object> objects = new SynchronousQueue<>();
        new Thread(()->{
            try {
                objects.put("a");
                System.out.println(Thread.currentThread().getName()+"put a");
                objects.put("b");
                System.out.println(Thread.currentThread().getName()+"put b");
                objects.put("c");
                System.out.println(Thread.currentThread().getName()+"put c");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"T1").start();

        new Thread(()->{
            try {
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+"->"+objects.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+"->"+objects.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+"->"+objects.take());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"T2").start();
    }
}

11.线程池(重点)

线程池:三大方法,七大参数,四种拒绝策略

池化技术

当程序允许时需要的链接如:JDBC链接，IO链接等等他们开启或关闭会极大的耗费资源,这时则引入了一个池化技术的概念。

池化技术本质:事先准备好一些资源,要用的时候来这里取,用完了在放回去,这样就不用一直开启关闭浪费资源了.

线程池的好处:

• 降低资源消耗
• 效率大大提升
• 方便我们管理

线程复用可以控制最大并发数,管理线程！

线程池三大方法

package JUC.Queue;

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

/**
 * 三大方法
 */
public class TestExecutors {
    public static void main(String[] args) {
//        ExecutorService executorService = Executors.newSingleThreadExecutor();//单个线程
//        ExecutorService executorService = Executors.newFixedThreadPool(100);//固定线程池大写
        ExecutorService executorService = Executors.newCachedThreadPool();//可伸缩的线程池
        try {
            for (int i = 0; i < 100; i++) {
                executorService.execute(()->{
                    System.out.println(Thread.currentThread().getName());
                });
            }
        } finally {
            //线程池用完一定要关闭
            executorService.shutdown();
        }
    }
}

七大参数

源码分析:

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

    //固定线程池大写
    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }
    
    //可伸缩的线程池
    public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE, //这里最大核心线程约为21亿!
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }

    //本质开启线程池调用了ThreadPoolExecutor()
    public ThreadPoolExecutor(int corePoolSize, //核心线程池大小
                              int maximumPoolSize,    //最大核心线程池大小
                              long keepAliveTime,     //超时了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，创建线程的，一般不动用
                              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.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

阿里规范手册！

手动创建一个线程池

package JUC.Queue;

import java.util.concurrent.*;

public class TestThreadPoolExecutor {
    public static void main(String[] args) {
        /**
         * 四种拒绝策略
         * 1.new ThreadPoolExecutor.AbortPolicy() //线程满了还有线程要进入则,不做处理,直接抛出异常
         * 2.new ThreadPoolExecutor.CallerRunsPolicy() //那来的那里去
         * 3.new ThreadPoolExecutor.DiscardPolicy() //队列满了丢掉任务,直接开摆,不会抛出异常!
         * 4.new ThreadPoolExecutor.DiscardOldestPolicy() //队列满了,尝试去和最早的竞争，也不会抛出异常!
         */
        ThreadPoolExecutor executor = new ThreadPoolExecutor(
                2,
                5,
                2,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(3),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.CallerRunsPolicy());//队列满了,尝试去和最早的竞争，也不会抛出异常!


        for (int i = 0; i < 19; i++) {
            executor.execute(()->{
                System.out.println(Thread.currentThread().getName()+"线程");
            });
        }
    }
}

四种拒绝策略

• new ThreadPoolExecutor.AbortPolicy() //线程满了还有线程要进入则,不做处理,直接抛出异常
• new ThreadPoolExecutor.CallerRunsPolicy() //那来的那里去
• new ThreadPoolExecutor.DiscardPolicy() //队列满了丢掉任务,直接开摆,不会抛出异常!
• new ThreadPoolExecutor.DiscardOldestPolicy() //队列满了,尝试去和最早的竞争，也不会抛出异常!

小结和拓展:

池的最大的线程如何去设置?

了解:IO密集型与CPU密集型

package JUC.Queue;

import java.util.concurrent.*;

public class TestThread {
    public static void main(String[] args) {
        /**
         * 最大线程到底该如何定义?
         * CPU密集型:CPU几核就是几 可以使用Runtime.getRuntime().availableProcessors()方法检测出电脑是几核的
         * IO密集型：判断程序中十分消耗资源的IO有多少个最大线程数大于它就好了(最好是它的两倍)
         */
        new ThreadPoolExecutor(1,
                Runtime.getRuntime().availableProcessors(),
                1,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(3),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.DiscardPolicy());
    }
}

12.四大函数式接口(必须掌握)

新时代的程序员:lambda表达式，链式编程，函数式接口，Stream流式计算

函数式接口:只有一个方法的接口

如:

package java.lang;

@FunctionalInterface
public interface Runnable {
    public abstract void run();
}
/**
 * FunctionalInterface超级多
 * 它简化了编程模板，在新版的框架底层大量运用
 * forEach(消费者类的函数式接口)
 */

Function函数式接口

package JUC.FunctionInterface;

import java.util.function.Function;

//Function测试
public class TestFunction {
    public static void main(String[] args) {
        //使用匿名内部类表示
        Function<Integer, String> function = new Function<>() {
            @Override
            public String apply(Integer o) {
                if (o!=null){
                    return String.valueOf(o);
                }else {
                    return null;
                }
            }
        };

        //使用lambda表达式优化
        Function<Integer,String> lambda=o->String.valueOf(o);
        
        System.out.println(lambda.apply(16));
    }
}

断定型接口：Predicate

package JUC.FunctionInterface;

import java.util.Objects;
import java.util.function.Predicate;

/**
 * 断定型接口：有一个输入参数返回值只能是Boolean值
 */
public class TestPredicate {
    public static void main(String[] args) {
        Predicate<String> predicate = new Predicate<>() {
            @Override
            public boolean test(String o) {
                return o.isEmpty();
            }
        };
        
        //简化
        Predicate<String> predicate1=(o)->{return o.isEmpty()};
    }
}

供给型接口:

package JUC.FunctionInterface;

import java.util.function.Supplier;

//供给型接口：只有返回值没有参数列表
public class TestSupplier {
    public static void main(String[] args) {
        
        Supplier<String> supplier = new Supplier<>() {
            @Override
            public String get() {
                return "你好";
            }
        };
        
        //简化
        Supplier<String> s=()-> "你好";
    }
}

13.Stream流式计算

什么是Stream计算

我们一些的集合与Mysql数据库本质是用来存储数据的,计算都应该交给流来操作！

package JUC.Stream;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.Arrays;
import java.util.List;
import java.util.Locale;
import java.util.stream.Stream;

/**
 * 题目:一分钟内完成此题,并且只能用一行代码来实现
 * 1.ID为偶数
 * 2.年龄必须大于23
 * 3.用户名转换为大写字母,并返回
 * 4.用户名字母倒着排序
 * 5.只输出一个用户
 */
public class practice<T> {
    public static void main(String[] args) {
        User user1 = new User(1,"a",21);
        User user2 = new User(2,"b",22);
        User user3 = new User(3,"c",23);
        User user4 = new User(4,"d",24);
        User user5 = new User(6,"e",25);
        Arrays.asList(user1, user2, user3, user4, user5)
                .stream()
                .filter(user -> {return user.id%2==0;})
                .filter(user -> { return user.age>23;})
                .map(user -> {return user.name.toUpperCase();})
                .sorted((uu1,uu2)->{return uu2.compareTo(uu1);})
                .limit(1)
                .forEach(System.out::print);

    }


}

//有参，无参构造,get,set,toString方法！
@Data
@NoArgsConstructor
@AllArgsConstructor
class User{
    int id;
    String name;
    int age;
}

14.ForkJoin

ForkJoin

ForkJoin在JDK1.7,并发执行任务！提高效率，大数据量！

大数据：Map Reduce(把大任务拆分为小任务)

ForkJoin的特点:工作窃取

这个里面维护的都是双端队列

ForkJoin操作:

package JUC.ForkJoin;

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

//测试
public class TestTime {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        test01();//385毫秒
        test02();//140毫秒
        test03();
    }

    //普通计算
    public static void test01(){
        long sum=0L;
        long stare = System.currentTimeMillis();
        for (int i = 1; i <= 10_0000_0000; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sun="+sum+",时间为:"+(end-stare)+"毫秒");
    }

    //使用ForkJoin
    public static void test02() throws ExecutionException, InterruptedException {
        long stare = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        TestForkJoin task = new TestForkJoin(1L, 10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);//提交任务
        Long sum = submit.get();
        long end = System.currentTimeMillis();
        System.out.println("sun="+sum+",时间为:"+(end-stare)+"毫秒");
    }

    //使用Stream流计算
    public static void test03(){
        long stare = System.currentTimeMillis();
        //range表示() 而rangeClosed表示(]
        long sum = LongStream.rangeClosed(1L, 10_0000_0000L).parallel().reduce(0, Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("sun="+sum+" 时间为:"+(end-stare)+"毫秒");
    }
}

package JUC.ForkJoin;

import java.util.concurrent.RecursiveTask;

/**
 * 求和计算的任务
 *
 * 如何使用ForkJoin?
 * 1.ForkJoinPool 通过它来执行
 * 2.计算任务 ForkJoinPool.execute(ForkJoinTask<?> task)
 * 3.计算类需要继承RecursiveTask抽象类
 */
public class TestForkJoin extends RecursiveTask<Long> {
    private final Long start;//起始值  1
    private final Long end;//结束的值   1990999

    //临界值
    private final Long temp=1000L;

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


    /**
     * 计算方法
     * @return 计算结果
     */
    @Override
    protected Long compute() {
        if ((end-start)<temp){
            long sum=0L;
            for (Long i = start; i <= end; i++) {
                sum+=i;
            }
            return sum;
        }else {
            //分支合并计算使用 ForkJoin
            long middle = (start+end)/ 2; //中间值
            TestForkJoin task1 = new TestForkJoin(start, middle);
            task1.fork();//拆分把任务压入线程队列
            TestForkJoin task2 = new TestForkJoin(middle+1, end);
            task2.fork();//拆分把任务压入线程队列
            return task1.join() + task2.join();
        }
    }
}

15.异步回调

Future设计初衷：

package JUC.Future;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
/**
 * 异步调用:CompletableFuture
 */
public class TestCompletableFuture {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(()->{
            System.out.println(Thread.currentThread().getName());
            int i = 10/0;
            return 1024;
        });
        //获取执行结果
        completableFuture.whenComplete((t,u)->{
            System.out.println("t->"+ t);
            System.out.println("u->"+u);
        }).exceptionally((e)->{
            System.out.println(e.getMessage());
            return 0;
        });

    }

}

16.JMM

请你谈谈你对volatile的理解

volatile是java虚拟机提供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

什么是JMM

JMM是java内存模型，不存在的东西,是概念,是约定.

关于JMM的一些同步约定:

1. 线程解锁前,必须立刻把共享遍历刷回主存
2. 线程加锁前,必须读取主存中的最新值到工作内存中
3. 加锁和解锁都是一把锁

如:

package JUC.JMM;

import java.util.concurrent.TimeUnit;

public class TestJMM {
    private static boolean flag=true;

    public static void main(String[] args) throws InterruptedException {
        new Thread(()->{
            while (flag){

            }
        }).start();

        System.out.println("停顿!");
        TimeUnit.SECONDS.sleep(1);
        flag=false;
        System.out.println("修改完毕!");
        //这里直接循环卡死!
    }
}

Volatile

1.保证可见性

package JUC.JMM;

import java.util.concurrent.TimeUnit;

public class TestJMM {
    //加入volatile可以保证程序的可见性
    private static volatile boolean flag=true;

    public static void main(String[] args) throws InterruptedException {
        new Thread(()->{ //该线程对主内存的变化是不可见的!
            while (flag){

            }
        }).start();

        System.out.println("停顿!");
        TimeUnit.SECONDS.sleep(1);
        flag=false;
        System.out.println("修改完毕!");
        //这里直接循环卡死!
    }
}

2.不保证原子性

原子性:不可分割

线程A在执行任务的时候不能被打扰的,也不能被分割,要么一起成功要么一起失败

package JUC.JMM;

public class TestJMM02 {

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

    public static void add(){
        flag++;
    }
    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    add();
                }
            }).start();
        }

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

如果不加Lock和synchronized如何保证原子性?

使用原子类:

package JUC.JMM;

import java.util.concurrent.atomic.AtomicInteger;

public class TestJMM02 {

    //volatile不保证原子性
    private volatile static AtomicInteger flag=new AtomicInteger();

    public static void add(){
        flag.getAndIncrement();//进行+1操作
    }
    public static  void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    add();
                }
            }).start();
        }

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

这些原子类的底层都是直接和操作系统挂钩！在内存中修改值！Unsafe是一个很特殊的存在！

指令重排：

什么是指令重排：你写的程序计算机并不是按照你写的程序去执行的！

源代码->编译器优化的重排->指令并行也可能会重排->内存系统也会重排->执行

int x=1; //1
int y=2; //2
x=x+3;   //3
y=y*x;   //4

我们所希望的是1234而但可能执行的时候会变成:2134,1324但不可能是4321因为处理器在进行指令重排的时候会考虑数据之间的依赖问题！

可能造成影响的结果: a,b,x.v四个值默认为0

正常结果:x,y都为0;但是可能由于指令重排:

指令重排可能导致的诡异结果:x=2,y=1.

Volatile则可以避免指令重排

使其加入了内存屏障，作用:

1.保证特定操作的执行顺序

2.可以保证某些内存表变量的可见性(利用这些特性Volatile实现了可见性)

Volatile可以保证,可见性,不保证原子性，由于内存屏障禁止了指令重排.

Volatile在单例模式下使用的最多！