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
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）
-
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