Java并发编程--基础进阶高级(完结)

Java并发编程--基础进阶高级完整笔记。

这都不知道是第几次刷狂神的JUC并发编程了,从第一次的迷茫到现在比较清晰,算是个大进步了,之前JUC笔记不见了,重新做一套笔记。

参考链接:https://www.bilibili.com/video/BV1B7411L7tE

Java并发编程--基础进阶高级(完结)
Java并发编程--基础进阶高级(完结)
Java并发编程--基础进阶高级(完结)
Java并发编程--基础进阶高级(完结)
Java并发编程--基础进阶高级(完结)


目录

1.多线程--基础内容

1.Thread状态

​ 6种:新建、运行、阻塞、等待、超时等待、结束(可点击Thread查看源代码)

public enum State {
NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED;
}
2.Synchronized
  • 非公平锁
  • 可重入锁,

​ Synchronized:是非公平锁(不能保证线程获得锁的顺序,即线程不会依次排队去获取资源,而是争抢,但是结果一定是正确的),是可重入锁(已获得一个锁,可以再获得锁且不会造成死锁,比如synchronized内部可以再写个synchronized函数)

    /**
* Author: HuYuQiao
* Description: Synchronized实现方式(修饰函数即可)
*/
class TicketSync{
public int number = 50;
//synchronized本质是队列,锁
public synchronized void sale(){
if(number > 0) {
System.out.println(Thread.currentThread().getName() + "获得了第" + number-- +"票");
}
}
}
3.Lock锁
  • 可重入锁

  • 公平还是不公平锁可以设置(默认不公平锁)

        /**
    * Creates an instance of {@code ReentrantLock} with the
    * given fairness policy.
    *
    * @param fair {@code true} if this lock should use a fair ordering policy
    */
    public ReentrantLock(boolean fair) {
    sync = fair ? new FairSync() : new NonfairSync();
    }

    Lock:加锁之后必须解锁,,否则其他线程就获取不到了,所以用try-catch-finally包起来。

    /**
* Author: HuYuQiao
* Description: Lock实现方式(加锁、解锁)
*/
class TicketLock{
Lock lock = new ReentrantLock();
public int number = 50;
public void sale(){
lock.lock();
try {
System.out.println(Thread.currentThread().getName() + "获得了第" + number-- +"票"); } catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
4.总结

​ 在不加锁情况下,多线程会争抢,导致输出顺序、计算结果都会不一致(上面例子结果如果一样是因为只有3个线程,for循环即出错,因为number--这个函数本身不是线程安全的),所以就引入了锁的概念,synchronized,lock保证了输出顺序、计算结果的一致性。

虚假唤醒:在synchronized.wait与lock.condition.await唤醒线程时,是从await代码之后开始运行,所以为了保证能唤醒线程,需要用while语句将代码包含起来。

​ 完整代码

package com.empirefree.springboot;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import sun.security.krb5.internal.Ticket; import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; /**
* @program: springboot
* @description: 多线程
* @author: huyuqiao
* @create: 2021/06/26 14:26
*/ @RunWith(SpringRunner.class)
@SpringBootTest
@Slf4j
public class ThreadTest { /**
* Author: HuYuQiao
* Description: Synchronized实现方式(修饰函数即可)
*/
class TicketSync{
public int number = 50;
//synchronized本质是队列,锁
public synchronized void sale(){
System.out.println(Thread.currentThread().getName() + "获得了第" + number-- +"票"); }
} /**
* Author: HuYuQiao
* Description: Lock实现方式(加锁、解锁)
*/
class TicketLock{
Lock lock = new ReentrantLock();
public int number = 50;
public void sale(){
lock.lock();
try {
System.out.println(Thread.currentThread().getName() + "获得了第" + number-- +"票"); } catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
} @Test
public void testThread() {
// TicketSync ticket = new TicketSync();
TicketLock ticket = new TicketLock();
new Thread( () ->{
for (int i = 0; i < 50; i++) {
ticket.sale();
} },"ThreadA").start();
new Thread(()->{
for (int i = 0; i < 50; i++) {
ticket.sale();
}
},"ThreadB").start();
new Thread(()->{
for (int i = 0; i < 50; i++) {
ticket.sale();
}
},"ThreadC").start(); for (int i = 0; i < 500; i++) {
new Thread(() -> {
ticket.sale();
}).start();
}
}
}

2.八锁现象(synchronized、static)

即synchronized、static修饰的函数,执行顺序、输出结果。

结果表明:

​ 1.synchronized修饰的函数:会锁住对象(可以看成锁对象中某个方法),看起来代码会依次执行,而没有锁的方法即不受影响,一来就先执行

​ 2.static synchronized修饰的函数:会锁住类.class(可以不同对象访问的都是同一个函数),所以2个对象访问自己的函数依然还是顺序执行.

​ 3.一个有static,一个没有static:即一个锁类.class,另一个锁对象,不管是同一个对象还是不同对象,就都不需要等待了,不会顺序执行。

1.synchronized

​ 修饰函数会保证同一对象依次顺序执行()

class Phone{
//synchronized
public synchronized void sendSms() {
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("sendSms");
}
public synchronized void call() {
System.out.println("call");
} public void playGame(){
System.out.println("playGame");
}
} public static void main(String[] args) {
//Thread--代码执行顺序问题
Phone phone = new Phone();
new Thread(phone::sendSms, "A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(phone::call, "B").start();
new Thread(phone::playGame, "C").start();
}
2.static synchronized
class PhoneStatic{
//static synchronized
public static synchronized void sendSmsStatic() {
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("sendSmsStatic");
}
public static synchronized void callStatic() {
System.out.println("callStatic");
}
} public static void main(String[] args) {
PhoneStatic phoneStatic = new PhoneStatic();
PhoneStatic phoneStatic2 = new PhoneStatic();
new Thread(() ->{
phoneStatic2.sendSmsStatic();
}, "A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(() ->{
phoneStatic2.callStatic();
}, "B").start();
}

3.Java集合--安全性

        //集合安全性--list,set,map都非线程安全
List<String> list = new Vector<>();
List<String> list = Collections.synchronizedList(new ArrayList<>());
List<String> list = new CopyOnWriteArrayList<>(); Map<String, String> objectObjectHashMap = new ConcurrentHashMap<>();
Map<Object, Object> objectObjectHashMap1 = Collections.synchronizedMap(new HashMap<>());
//set底层就是map:无论hashset还是linkedhashset
Set<String> set = Collections.synchronizedSet(new LinkedHashSet<>());
Set<String> set = new CopyOnWriteArraySet<>();

4.高并发--辅助类

​ 学习链接:https://www.cnblogs.com/meditation5201314/p/14395972.html

1.countdownLatch

Countdownlatch:减一操作,直到为0再继续向下执行

package Kuangshen.JUC.Thread;

import java.util.concurrent.CountDownLatch;

public class countDownLatch {
public static void main(String[] args) throws InterruptedException { final CountDownLatch countDownLatch = new CountDownLatch(5); for (int i = 0; i < 5; i++) {
new Thread(() -> {
System.out.println(Thread.currentThread().getName() + "get out");
countDownLatch.countDown();
}, String.valueOf(i)).start();
}
countDownLatch.await(); //等待上述执行完毕再向下执行
System.out.println("close door");
}
}
2.cyclicbarrier

Cyclicbarrier:+1操作,对于每个线程都自动+1并等待,累计到规定值再向下执行,

package Kuangshen.JUC.Thread;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier; /**
* @author :Empirefree
* @description:TODO
* @date :2021/2/10 10:56
*/
public class cyclicbarrier {
public static void main(String[] args) throws BrokenBarrierException, InterruptedException {
//CyclicBarrier里面是容量 + runnable
final CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () ->{
System.out.println("不断增加到7即向后执行,与countdownlatch相反");
}
); /*对于指派的局部变量,lambda只能捕获一次 ,故而需定义成final(int内部定义就是final),而且线程中,
不能对局部变量进行修改,如需要修改,需定义成原子类atomic
*/
for (int i = 0; i < 7; i++) {
int finalI = i;
new Thread(() ->{
System.out.println(finalI);
try {
cyclicBarrier.await();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
} }).start();
}
} }
3.semaphore

semaphore:对于规定的值,多个线程只规定有指定的值能获取,每次获取都需要最终释放,保证一定能互斥执行

package Kuangshen.JUC.Thread;

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit; /**
* @author :Empirefree
* @description:TODO
* @date :2021/2/10 15:24
*/
public class semaphore {
public static void main(String[] args) {
final Semaphore semaphore = new Semaphore(3); for (int i = 0; i < 60; i++) {
new Thread(() -> {
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 {
semaphore.release();
}
}).start();
}
}
}

5.读写锁(ReadWriteLock)

​ ReadWriteLock也是多线程下的一种加锁方式,下面列出ReadWriteLock和synchronized对多线程下,保证读完之后在写的实现方式

//读写锁 :写只有一个线程写,写完毕后 可以多个线程读
MyCache myCache = new MyCache();
int num = 6;
for (int i = 1; i < num; i++) {
int finalI = i;
new Thread(()->{
myCache.write(String.valueOf(finalI),String.valueOf(finalI)); },String.valueOf(i)).start();
}
for (int i = 1; i < num; i++) {
int finalI = i;
new Thread(()->{
myCache.read(String.valueOf(finalI));
},String.valueOf(i)).start();
} class MyCache{
private volatile Map<String,String> map = new HashMap<>();
private ReadWriteLock lock = new ReentrantReadWriteLock();
//存,写
public void write(String key,String value){
lock.writeLock().lock(); //写锁
try { System.out.println(Thread.currentThread().getName()+"线程开始写入");
map.put(key,value);
System.out.println(Thread.currentThread().getName()+"线程开始写入ok");
} catch (Exception e){
e.printStackTrace();
} finally {
lock.writeLock().unlock();
}
}
//取,读
public void read(String key){
lock.readLock().lock(); //读锁
try { System.out.println(Thread.currentThread().getName()+"线程开始读取");
map.get(key);
System.out.println(Thread.currentThread().getName()+"线程读取ok");
} catch (Exception e){
e.printStackTrace();
} finally {
lock.readLock().unlock();
}
} //存,写
public synchronized void writeSync(String key,String value){
try {
System.out.println(Thread.currentThread().getName()+"线程开始写入");
map.put(key,value);
System.out.println(Thread.currentThread().getName()+"线程开始写入ok");
} catch (Exception e){
e.printStackTrace();
}
}
//取,读
public void readSync(String key){
try {
System.out.println(Thread.currentThread().getName()+"线程开始读取");
map.get(key);
System.out.println(Thread.currentThread().getName()+"线程读取ok");
} catch (Exception e){
e.printStackTrace();
}
}
}

6.线程池

1.集合--队列(阻塞队列、同步队列)

Java并发编程--基础进阶高级(完结)

  • 阻塞队列:blockingQueue(超时等待--抛弃,所以最后size=1)

            //阻塞队列
    ArrayBlockingQueue<String> arrayBlockingQueue = new ArrayBlockingQueue<>(1);
    arrayBlockingQueue.offer("a", 2, TimeUnit.SECONDS);
    arrayBlockingQueue.offer("a", 2, TimeUnit.SECONDS);
    System.out.println("超时等待==" + arrayBlockingQueue.size());
  • 同步队列:synchronizeQueue(类似于生产者消费者)

            //同步队列
    SynchronousQueue<String> synchronousQueue = new SynchronousQueue<>();
    new Thread(()->{
    try {
    System.out.println(Thread.currentThread().getName()+"put 01");
    synchronousQueue.put("1");
    System.out.println(Thread.currentThread().getName()+"put 02");
    synchronousQueue.put("2");
    System.out.println(Thread.currentThread().getName()+"put 03");
    synchronousQueue.put("3");
    } catch (InterruptedException e) {
    e.printStackTrace();
    }
    }).start();
    new Thread(()->{
    try {
    System.out.println(Thread.currentThread().getName()+"take"+synchronousQueue.take());
    System.out.println(Thread.currentThread().getName()+"take"+synchronousQueue.take());
    System.out.println(Thread.currentThread().getName()+"take"+synchronousQueue.take());
    } catch (InterruptedException e) {
    e.printStackTrace();
    }
    }).start();
2.线程池基本概念(三大方法、七大参数、四种拒绝策略)
  • 三大方法:newSingleThreadExecutro(单个线程),newFixedThreadPool(固定大小线程池),newCachedThreadPool(可伸缩)

     ExecutorService threadPool = Executors.newSingleThreadExecutor();
    ExecutorService threadPool2 = Executors.newFixedThreadPool(5);
    ExecutorService threadPool3 = Executors.newCachedThreadPool();
  • 七大参数:

    ThreadPoolExecutor(int corePoolSize,  //核心线程池大小
    int maximumPoolSize, //最大的线程池大小(当阻塞队列满了就会打开)
    long keepAliveTime, //(空闲线程最大存活时间:即最大线程池中有空闲线程超过这个时间就会释放线程,避免资源浪费)
    TimeUnit unit, //超时单位
    BlockingQueue<Runnable> workQueue, //阻塞队列
    ThreadFactory threadFactory, //线程工厂 创建线程的 一般不用动
    RejectedExecutionHandler handler //拒绝策略
  • 四种拒绝策略:

    new ThreadPoolExecutor.AbortPolicy: // 该 拒绝策略为:银行满了,还有人进来,不处理这个人的,并抛出异常
    new ThreadPoolExecutor.CallerRunsPolicy(): // //该拒绝策略为:哪来的去哪里 main线程进行处理
    new ThreadPoolExecutor.DiscardPolicy(): //该拒绝策略为:队列满了,丢掉异常,不会抛出异常。
    new ThreadPoolExecutor.DiscardOldestPolicy(): //该拒绝策略为:队列满了,尝试去和最早的进程竞争,不会抛出异常

7.Stream(4个函数式接口、Lambda、异步回调)

1.函数式接口

​ 学习链接:https://www.cnblogs.com/meditation5201314/p/13693089.html

2.Lambda表达式

​ 学习链接:https://www.cnblogs.com/meditation5201314/p/13651755.html

3.异步回调
        //异步回调--无返回值
CompletableFuture<Void> future = CompletableFuture.runAsync(() ->{
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "....");
});
System.out.println("begin");
System.out.println(future.get());
System.out.println("end"); //异步回调--有返回值
CompletableFuture<Integer> future2 = CompletableFuture.supplyAsync(() ->{
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
return 3;
});
System.out.println("begin");
System.out.println(future2.get());
System.out.println(future2.whenComplete((result, error) ->{
System.out.println("返回结果:" + result);
System.out.println("错误结果" + error);
}).exceptionally(throwable -> {
System.out.println(throwable.getMessage());
return 502;
}).get());
System.out.println("end");

8.单例模式

1.饿汉模式(程序一启动就new,十分占内存)
/**
* @program: untitled
* @description: 单例模式
* @author: huyuqiao
* @create: 2021/06/27 14:44
*/ public class SingleModel { /*
* 可能会浪费空间
* */
private byte[] data1 = new byte[1024*1024];
private byte[] data2 = new byte[1024*1024];
private byte[] data3 = new byte[1024*1024];
private byte[] data4 = new byte[1024*1024];
private static final SingleModel hugrySingle = new SingleModel();
private SingleModel(){ }
public static SingleModel getInstance(){
return hugrySingle;
}
}
2.懒汉模式(DCL模式:双重检测,需要的时候才new)

1.第一层if没有加锁,所以会有多个线程到达if

2.如果内部new对象指令重排,就会导致有些线程认为lazyManModel有对象,所以会直接返回lazyManModel(实际为null)

3.所以需要加上valitile防止指令重排

/**
* @program: untitled
* @description: 懒汉式
* @author: huyuqiao
* @create: 2021/06/27 15:06
*/ public class LazyManModel {
private volatile static LazyManModel lazyManModel;
private LazyManModel(){
System.out.println(Thread.currentThread().getName() + "...");
} //DCL懒汉式:双重检测锁--实现效果,只有为空的才null,否则不用null,所以需要2重if判断。
public static LazyManModel getInstance(){
if (lazyManModel == null){
synchronized (LazyManModel.class){
if (lazyManModel == null){
lazyManModel = new LazyManModel();
}
}
}
return lazyManModel;
} public static void main(String[] args) {
for (int i = 0; i < 10; i++) {
new Thread(() ->{
LazyManModel.getInstance();
}).start();
}
}
}

9.Volatile和Atomic

​ 学习笔记:https://www.cnblogs.com/meditation5201314/p/13707590.html

10.Java中锁

1.公平锁(FIFO):Lock锁可以自定义,synchronized
2.非公平锁(允许插队):Lock锁可以自定义
3.可重入锁(获取一个锁再获取其他锁不会造成死锁):lock锁和synchronized
4.自旋锁:得不到就一直等待(Atomic.getAndIncrement底层就是自旋锁)
import java.util.Collections;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantLock; /**
* @program: untitled
* @description: spinlock
* @author: huyuqiao
* @create: 2021/06/27 15:40
*/ public class SpinLockTest {
public static void main(String[] args) throws InterruptedException { //使用CAS实现自旋锁
SpinlockDemo spinlockDemo=new SpinlockDemo();
new Thread(()->{
spinlockDemo.myLock();
try {
TimeUnit.SECONDS.sleep(3);
} catch (Exception e) {
e.printStackTrace();
} finally {
spinlockDemo.myUnlock();
}
},"t1").start(); TimeUnit.SECONDS.sleep(1); new Thread(()->{
spinlockDemo.myLock();
try {
TimeUnit.SECONDS.sleep(3);
} catch (Exception e) {
e.printStackTrace();
} finally {
spinlockDemo.myUnlock();
}
},"t2").start();
}
} class SpinlockDemo { // 默认
// int 0
//thread null
AtomicReference<Thread> atomicReference=new AtomicReference<>(); //加锁
public void myLock(){
Thread thread = Thread.currentThread();
System.out.println(thread.getName()+"===> mylock"); //自旋锁--为空则返回true,否则返回false
while (!atomicReference.compareAndSet(null,thread)){
System.out.println(Thread.currentThread().getName()+" ==> .自旋中~");
}
} //解锁
public void myUnlock(){
Thread thread=Thread.currentThread();
System.out.println(thread.getName()+"===> myUnlock");
atomicReference.compareAndSet(thread,null);
} }
5.死锁命令排查
jps -l
jstack 进程号
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