java.util工具包
业务:普通的线程代码 Thread
Runnable 没有返回值,效率相比于Callable相对较低!
线程、进程
进程:
线程
java真的能开启线程吗? 不能
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 */
}
}
}
//本地方法,调运的是底层的c++,java无法直接操作硬件
private native void start0();
并发、并行
并发(多线程操作同一资源)
并行(多个人一起行走)
package com.swan.demo01;
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(6种)
public enum State {
// 新生
NEW,
//运行
RUNNABLE,
//阻塞
BLOCKED,
//等待
WAITING,
//超时等待
TIMED_WAITING,
//终止
TERMINATED;
}
wait/sleep 区别
传统 synchronized
package com.swan.demo01;
// 基本的买票例子
/**
* 真正的多线程
* 线程就是一个单独的资源类,没有任何附属操作
*
*/
public class SaleTicketDemo01 {
public static void main(String[] args) {
// 并发:多线程操作同一个资源类
Ticket ticket = new Ticket();
new Thread(() -> {
for (int i = 0; i < 40; i++) {
ticket.sale();
}
},"A").start();
new Thread(() -> {
for (int i = 0; i < 40; i++) {
ticket.sale();
}
},"B").start();
new Thread(() -> {
for (int i = 0; i < 40; i++) {
ticket.sale();
}
},"C").start();
}
}
// 资源类 OOP
class Ticket {
//属性、方法
private int number = 30;
// 买票的方式
//synchronized 本质:队列,锁
public synchronized void sale(){
if (number > 0){
System.out.println(Thread.currentThread().getName()+"卖出了"+(number--) + "票,剩余:"+number);
}
}
}
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)
package com.swan.demo01;
// 基本的买票例子
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 真正的多线程
* 线程就是一个单独的资源类,没有任何附属操作
*
*/
public class SaleTicketDemo02 {
public static void main(String[] args) {
// 并发:多线程操作同一个资源类
Ticket2 ticket = new Ticket2();
new Thread(() -> { for (int i = 0; i < 40; i++) ticket.sale(); },"A").start();
new Thread(() -> { for (int i = 0; i < 40; i++) ticket.sale(); },"B").start();
new Thread(() -> { for (int i = 0; i < 40; i++) ticket.sale(); },"C").start();
}
}
// 资源类 OOP
//lock锁
// 1 new ReentrantLock();
// 2 加锁
// 3 解锁
class Ticket2 {
//属性、方法
private int number = 30;
Lock lock = new ReentrantLock();
// 买票的方式
public synchronized void sale(){
lock.lock(); //加锁
try {
//业务代码
if (number > 0){
System.out.println(Thread.currentThread().getName()+"卖出了"+(number--) + "票,剩余:"+number);
}
}catch (Exception e){
e.printStackTrace();
} finally {
lock.unlock(); //解锁
}
}
}
synchronized 和 Lock 区别
锁是什么?如何判断锁的是谁
生产者和消费者问题 Synchronized 版
package com.swan.pc;
/**
* 线程之间的通信问题:生产者和消费者问题 等待唤醒 通知唤醒
* 线程交替执行 A B 操作同一个变量 num = 0
* A num + 1
* B num - 1
*/
public class A {
public static void main(String[] args) {
Data data = new Data();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"B").start();
}
}
//数字 资源类
// 等待 业务 通知
class Data{
private int number = 0;
// +1
public synchronized void increment() throws InterruptedException {
if (number != 0){
//等待操作
this.wait();
}
number ++;
System.out.println(Thread.currentThread().getName()+"=>"+number);
// 通知其他线程 我+1 完毕了
this.notifyAll();
}
// -1
public synchronized void decrement() throws InterruptedException {
if (number == 0){
//等待操作
this.wait();
}
number --;
System.out.println(Thread.currentThread().getName()+"=>"+number);
// 通知其他线程 我-1 完毕了
this.notifyAll();
}
}
问题存在 A B C D 4个线!虚假唤醒
package com.swan.pc;
/**
* 线程之间的通信问题:生产者和消费者问题 等待唤醒 通知唤醒
* 线程交替执行 A B 操作同一个变量 num = 0
* A num + 1
* B num - 1
*/
public class A {
public static void main(String[] args) {
Data data = new Data();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"B").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"C").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"D").start();
}
}
//数字 资源类
// 等待 业务 通知
class Data{
private int number = 0;
// +1
public synchronized void increment() throws InterruptedException {
while (number != 0){
//等待操作
this.wait();
}
number ++;
System.out.println(Thread.currentThread().getName()+"=>"+number);
// 通知其他线程 我+1 完毕了
this.notifyAll();
}
// -1
public synchronized void decrement() throws InterruptedException {
while (number == 0){
//等待操作
this.wait();
}
number --;
System.out.println(Thread.currentThread().getName()+"=>"+number);
// 通知其他线程 我-1 完毕了
this.notifyAll();
}
}
JUC 版生产者和消费者问题
通过Lock找到Condition
代码实现:当时代码跑起来一直会陷入等待中,没有测试成功
package com.swan.pc;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 线程之间的通信问题:生产者和消费者问题 等待唤醒 通知唤醒
* 线程交替执行 A B 操作同一个变量 num = 0
* A num + 1
* B num - 1
*/
public class B {
public static void main(String[] args) {
Data2 data = new Data2();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"B").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"C").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"D").start();
}
}
//数字 资源类
// 等待 业务 通知
class Data2{
private int number = 0;
Lock lock = new ReentrantLock();
Condition condition = lock.newCondition();
// +1
public synchronized void increment() throws InterruptedException {
lock.lock();
try {
while (number != 0){
//等待操作
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();
}
}
// -1
public synchronized void decrement() throws InterruptedException {
lock.lock();
try {
while (number == 0){
//等待操作
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();
}
}
}
Condition 精准的通知和唤醒线程
package com.swan.pc;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 线程之间的通信问题
* A -> B -> C -> A 按次序执行
*/
public class C {
public static void main(String[] args) {
Data3 data = new Data3();
new Thread(()->{
for (int i = 0; i < 10; i++) {
data.printA();
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
data.printB();
}
},"B").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
data.printC();
}
},"C").start();
}
}
//数字 资源类
// 等待 业务 通知
class Data3{
private int number = 1; // 1A 2B 3C
Lock lock = new ReentrantLock();
Condition condition1 = lock.newCondition();
Condition condition2 = lock.newCondition();
Condition condition3 = lock.newCondition();
public void printA(){
lock.lock();
try {
while (number != 1){
condition1.await();
}
System.out.println(Thread.currentThread().getName()+" =>aaaaaa");
//唤醒指定的人
number = 2;
condition2.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printB(){
lock.lock();
try {
while (number != 2){
condition2.await();
}
System.out.println(Thread.currentThread().getName()+" =>aaaaaa");
//唤醒指定的人
number = 3;
condition3.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printC(){
lock.lock();
try {
while (number != 3){
condition3.await();
}
System.out.println(Thread.currentThread().getName()+" =>aaaaaa");
//唤醒指定的人
number = 1;
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
如何判断锁的是谁!永远知道什么是锁,锁到底锁的是谁!
深刻理解锁
package com.swan.lock8;
import java.util.concurrent.TimeUnit;
/**
* 8锁 就是关于锁的8个问题
* 1、标准情况下,两个线程先打印发短信还是打电话?1/发短信 2/打电话 =》 发短信
* 2、sendSms延迟4秒,两个线程先打印发短信还是打电话?1/发短信 2/打电话 =》 发短信
*/
public class Test1 {
public static void main(String[] args) {
Phone phone = new Phone();
new Thread(()->{phone.sendSms();},"A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(()->{phone.call();},"A").start();
}
}
class Phone{
// synchronized 锁的对象是方法的调用者
//两个方法用的是同一把锁,谁先拿到谁先执行
public synchronized void sendSms(){
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
public synchronized void call(){
System.out.println("打电话");
}
}
package com.swan.lock8;
import java.util.concurrent.TimeUnit;
/**
* 8锁 就是关于锁的8个问题
* 3、增加了一个普通方法后,先执行发短信还是hello?1/发短信 2/hello =》 hello(普通方法)
* 4、两个对象,两个同步方法,先执行发短信还是打电话?1/发短信 2/打电话 =》 打电话
*/
public class Test2 {
public static void main(String[] args) {
//两个对象,两个不同的调运者,两把锁
Phone2 phone = new Phone2();
Phone2 phone2 = new Phone2();
new Thread(()->{phone.sendSms();},"A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(()->{phone2.call();},"A").start();
}
}
class Phone2{
// synchronized 锁的对象是方法的调用者
public synchronized void sendSms(){
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
public synchronized void call(){
System.out.println("打电话");
}
//这里没有锁!不是同步方法,不受锁的影响
public void hello(){
System.out.println("hello");
}
}
package com.swan.lock8;
import java.util.concurrent.TimeUnit;
/**
* 8锁 就是关于锁的8个问题
* 5、增加两个静态的同步方法,只有一个对象,先执行发短信还是打电话?1/发短信 2/打电话 =》 发短信
* 6、两个对象!增加两个静态的同步方法,只有一个对象,先执行发短信还是打电话?1/发短信 2/打电话 =》 发短信
*/
public class Test3 {
public static void main(String[] args) {
//两个对象的class类模板只有一个,static,锁的是class
Phone3 phone = new Phone3();
Phone3 phone2 = new Phone3();
new Thread(()->{phone.sendSms();},"A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(()->{phone2.call();},"A").start();
}
}
class Phone3{
// synchronized 锁的对象是方法的调用者
// static 静态方法,类一加载就有了!锁的是class
public static synchronized void sendSms(){
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
public static synchronized void call(){
System.out.println("打电话");
}
}
package com.swan.lock8;
import java.util.concurrent.TimeUnit;
/**
* 8锁 就是关于锁的8个问题
* 7、1个静态同步方法,一个普通同步方法,只有一个对象,先执行发短信还是打电话?1/发短信 2/打电话 =》 打电话
* 8、1个静态同步方法,一个普通同步方法,2个对象,先执行发短信还是打电话?1/发短信 2/打电话 =》 打电话
*/
public class Test4 {
public static void main(String[] args) {
//
Phone4 phone = new Phone4();
Phone4 phone2 = new Phone4();
new Thread(()->{phone.sendSms();},"A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(()->{phone2.call();},"A").start();
}
}
class Phone4{
// 静态同步方法,锁的是class模板
public static synchronized void sendSms(){
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
//普通同步方法,锁的是方法调运者
public synchronized void call(){
System.out.println("打电话");
}
}
小结
new: this 具体的一个手机
static: class 唯一的一个模板
package com.swan.unsafe;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;
// java.util.ConcurrentModificationException 并发修改异常
public class ListTest {
public static void main(String[] args) {
// 并发下 ArrayList 是不安全的
/**
* 解决方案:
* 1、List list = new Vector<>();
* 2、List list = Collections.synchronizedList(new ArrayList<>());
* 3、List list = new CopyOnWriteArrayList<>();
*/
//CopyOnWrite 写入时复制 COW 计算机程序设计领域的一种优化策略;
// 多个线程调用的时候,list,读取的时候,固定的,写入(覆盖)
//在写入的时候避免覆盖,造成数据问题
// CopyOnWriteArrayList 比 Vector 好在哪里?读写分离
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();
}
}
}
package com.swan.unsafe;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.CopyOnWriteArraySet;
/**
* java.util.ConcurrentModificationException 并发修改异常
*/
public class SetTest {
public static void main(String[] args) {
// 并发下 HashSet 是不安全的
/**
* 解决方案:
* 1、Set
// Set set = new HashSet<>();
Set<Object> set = new CopyOnWriteArraySet<>();
for (int i = 0; i < 30; i++) {
new Thread(()->{
set.add(UUID.randomUUID().toString().substring(0,5));
System.out.println(set);
},String.valueOf(i)).start();
}
}
}
hashSet的底层是什么?
public HashSet() {
map = new HashMap<>();
}
//add set 本质就是 map key是无法重复的!
public boolean add(E e) {
return map.put(e, PRESENT)==null;
}
private static final Object PRESENT = new Object(); //不变的值
package com.swan.unsafe;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
// ConcurrentModificationException
public class MapTest {
public static void main(String[] args) {
//map 是这样用的吗?不是,工作中不用 HashMap
// 默认等价于什么?new HashMap<>(16,0.75);
/**
* 并发下:HashMap是不安全的 解决方案:
* 1、Map map = new ConcurrentHashMap<>();
*/
Map<String, String> map = new ConcurrentHashMap<>();
for (int i = 0; i < 30; i++) {
new Thread(()->{
map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0,5));
System.out.println(map);
},String.valueOf(i)).start();
}
}
}
package com.swan.callable;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
public class CallableTest {
public static void main(String[] args) throws ExecutionException, InterruptedException {
MyThread myThread = new MyThread();
FutureTask futureTask = new FutureTask(myThread);
//适配类
new Thread(futureTask,"A").start(); // 怎么启动 Callable
String str = (String) futureTask.get(); //获取Callable的返回结果,可能会产生阻塞!
System.out.println(str);
}
}
class MyThread implements Callable<String> {
@Override
public String call() throws Exception {
System.out.println("call()");
return "123";
}
}
细节:
package com.swan.add;
import java.util.concurrent.CountDownLatch;
// 计数器
public class CountDownLatchDemo {
public static void main(String[] args) throws InterruptedException {
//总数是6,必须要执行任务的时候在使用
CountDownLatch countDownLatch = new CountDownLatch(6);
for (int i = 0; i < 6; i++) {
new Thread(()->{
System.out.println(Thread.currentThread().getName()+"离开了");
countDownLatch.countDown(); //数量减一
},String.valueOf(i)).start();
}
countDownLatch.await(); //等待计数器归0,然后在向下执行
System.out.println("关门");
}
}
原理:
countDownLatch.countDown();
//数量减一
countDownLatch.await();
//等待计数器归0,然后在向下执行
每次有线程调用countDown(); 数量减一,假设计数器变为0,countDownLatch.await();
方法就会被唤醒,继续执行
package com.swan.add;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
/**
* 集齐7颗龙珠召唤神龙
*/
public class CyclicBarrierDemo {
public static void main(String[] args) {
// 召唤神龙的线程
CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> {
System.out.println("召唤神龙的成功");
});
for (int i = 0; i < 7; i++) {
final int temp = i;
//lambda 能操作到i吗
new Thread(()->{
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();
}
}
}
package com.swan.add;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
public class SemaphoreDemo {
public static void main(String[] args) {
//线程数量,停车位!限流
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 {
semaphore.release();// release() 释放
}
},String.valueOf(i)).start();
}
}
}
原理
semaphore.acquire();
获得,假设如果已经满了,等待,等待被释放为止!
semaphore.release();
释放,会将当前信号量释放 +1
作用:多个共享资源互斥的使用!并发限流,控制最大线程数!
package com.swan.rw;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* 独占锁(写锁)一次只能被一个线程占用
* 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) {
MyCacheLock myCache = new MyCacheLock();
//写入
for (int i = 0; i < 5; i++) {
int finalI = i;
new Thread(()->{
myCache.put(finalI+"",finalI+"");
},String.valueOf(i)).start();
}
//读取
for (int i = 0; i < 5; i++) {
int finalI = i;
new Thread(()->{
myCache.get(finalI+"");
},String.valueOf(i)).start();
}
}
}
/**
* 自定义缓存:加锁
*/
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,写入的时候只希望同时只有一个线程写
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
public Object get(String key){
readWriteLock.readLock().lock();
Object o = null;
try {
System.out.println(Thread.currentThread().getName()+"读取"+key);
o = map.get(key);
System.out.println(Thread.currentThread().getName()+"读取OK");
} catch (Exception e) {
e.printStackTrace();
} finally {
readWriteLock.readLock().unlock();
}
return o;
}
}
/**
* 自定义缓存
*/
class MyCache {
private volatile Map<String,Object> map = new HashMap<>();
//存
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
public Object 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");
return o;
}
}
阻塞队列:
BlockingQueue 不是新东西
什么情况下我们会使用 阻塞队列:多线程并发处理,线程池
方式 | 抛出异常 | 有返回值,不抛出异常 | 阻塞等待 | 超时等待 |
---|---|---|---|---|
添加 | add | offer() | put() | offer(“d”,2, TimeUnit.SECONDS) |
移出 | remove | poll() | take() | poll(2, TimeUnit.SECONDS) |
检测队首元素 | element | peek() | - | - |
/**
* 抛出异常
*/
public static void test1(){
//队列的大小
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.add("a"));
System.out.println(blockingQueue.add("b"));
System.out.println(blockingQueue.add("c"));
//IllegalStateException: Queue full 抛出异常
//System.out.println(blockingQueue.add("d"));
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
//NoSuchElementException
System.out.println(blockingQueue.remove());
}
/**
*有返回值,不抛出异常
*/
public static void test2(){
//队列的大小
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.offer("a"));
System.out.println(blockingQueue.offer("b"));
System.out.println(blockingQueue.offer("c"));
System.out.println(blockingQueue.offer("d")); // false 不抛出异常
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll()); // null 不抛出异常
}
/**
* 阻塞等待(一直阻塞)
*/
public static void test3() throws InterruptedException {
//队列的大小
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
//一直阻塞
blockingQueue.put("a");
blockingQueue.put("b");
blockingQueue.put("c");
// blockingQueue.put("d"); // 队列没有位置了,一直阻塞
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,一直阻塞
}
/**
* 阻塞等待(等待超时)
*/
public static void test4() throws InterruptedException {
//队列的大小
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
System.out.println("===============");
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll(2, TimeUnit.SECONDS)); // null 不抛出异常
}
没有容量,进去一个元素,必须等待取出来之后,才能在进去一个元素
package com.swan.bq;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;
/**
* 同步队列demo
*/
public class SynchronousQueueDemo {
public static void main(String[] args) {
SynchronousQueue<String> synchronousQueue = new SynchronousQueue<>();//同步队列
new Thread(()->{
try {
System.out.println(Thread.currentThread().getName()+" put 1");
synchronousQueue.put("1");
System.out.println(Thread.currentThread().getName()+" put 2");
synchronousQueue.put("2");
System.out.println(Thread.currentThread().getName()+" put 3");
synchronousQueue.put("3");
} catch (InterruptedException e) {
e.printStackTrace();
}
},"T1").start();
new Thread(()->{
try {
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+"=>"+synchronousQueue.take());
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+"=>"+synchronousQueue.take());
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+"=>"+synchronousQueue.take());
} catch (InterruptedException e) {
e.printStackTrace();
}
},"T2").start();
}
}
线程池:三大方法、7大参数、4种拒绝策略
池化技术
程序的运行,本质:占用系统的资源!优化资源的使用!=> 池化技术
线程池、连接池、内存池、对象池。。。
池化技术: 事先准备好一些资源,有人要用,就来我这里来拿,用完之后还给我。
线程池的好处
线程复用、控制最大并发数、管理线程
package com.swan.pool;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
* Executors 工具类,3大方法
* 使用了线程池之后,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); //创建一个固定的线程池大小
ExecutorService threadPool =Executors.newCachedThreadPool(); //可伸缩的线程池
try {
for (int i = 0; i < 100; i++) {
//使用了线程池之后,使用线程池来创建线程
threadPool.execute(()->{
System.out.println(Thread.currentThread().getName()+ " OK");
});
}
} catch (Exception e) {
e.printStackTrace();
} finally {
//关闭线程池
threadPool.shutdown();
}
}
}
源码分析
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 没有人调运了 就会释放
TimeUnit unit, //超时单位
BlockingQueue<Runnable> workQueue, // 阻塞队列
ThreadFactory threadFactory, // 线程工厂
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;
}
package com.swan.pool;
import java.util.concurrent.*;
/**
* Executors 工具类,3大方法
* 使用了线程池之后,使用线程池来创建线程
* 四大策略:
* 1 new ThreadPoolExecutor.AbortPolicy() //银行满了,还有人进来,不处理这个人的,抛出异常
* 2 new ThreadPoolExecutor.CallerRunsPolicy() //那来的去哪里
* 3 new ThreadPoolExecutor.DiscardPolicy() //队列满了,丢掉任务,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
*/
public class Demo01 {
public static void main(String[] args) {
//自定义线程池
//最大线程到底该如何定义
// 1 cpu 密集型 ,几核,就是几,可以保证CPU的效率最高 Runtime.getRuntime().availableProcessors()
// 2 IO 密集型,> 判断你程序中十分耗 IO 的线程
// 程序 15个大型任务 IO十分占资源!
ExecutorService threadPool = new ThreadPoolExecutor(
2,
Runtime.getRuntime().availableProcessors(), //获取CPU核数
3,
TimeUnit.SECONDS,
new LinkedBlockingDeque<>(3),
Executors.defaultThreadFactory(),
new ThreadPoolExecutor.DiscardOldestPolicy()); //队列满了,尝试去和最早的竞争,也不会抛出异常
try {
for (int i = 0; i < 9; i++) {
//使用了线程池之后,使用线程池来创建线程
threadPool.execute(()->{
System.out.println(Thread.currentThread().getName()+ " OK");
});
}
} catch (Exception e) {
e.printStackTrace();
} finally {
//关闭线程池
threadPool.shutdown();
}
}
}
/**
* 1 new ThreadPoolExecutor.AbortPolicy() //银行满了,还有人进来,不处理这个人的,抛出异常
* 2 new ThreadPoolExecutor.CallerRunsPolicy() //那来的去哪里
* 3 new ThreadPoolExecutor.DiscardPolicy() //队列满了,丢掉任务,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
*/
小结和拓展
了解: IO 密集型、CPU密集型:(调优)
package com.swan.pool;
import java.util.concurrent.*;
public class Demo01 {
public static void main(String[] args) {
//自定义线程池
//最大线程到底该如何定义?
// 1 cpu 密集型 ,几核,就是几,可以保证CPU的效率最高 Runtime.getRuntime().availableProcessors()
// 2 IO 密集型,> 判断你程序中十分耗 IO 的线程
// 程序 15个大型任务 IO十分占资源!
ExecutorService threadPool = new ThreadPoolExecutor(
2,
Runtime.getRuntime().availableProcessors(), //获取CPU核数
3,
TimeUnit.SECONDS,
new LinkedBlockingDeque<>(3),
Executors.defaultThreadFactory(),
new ThreadPoolExecutor.DiscardOldestPolicy()); //队列满了,尝试去和最早的竞争,也不会抛出异常
try {
for (int i = 0; i < 9; i++) {
//使用了线程池之后,使用线程池来创建线程
threadPool.execute(()->{
System.out.println(Thread.currentThread().getName()+ " OK");
});
}
} catch (Exception e) {
e.printStackTrace();
} finally {
//关闭线程池
threadPool.shutdown();
}
}
}
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
@FunctionalInterface
public interface Runnable {
public abstract void run();
}
//超级多FunctionalInterface
//简化编程模型,在新版本的框架底层大量应用
//forEach(消费者类的函数式接口)
package com.swan.function;
import java.util.function.Function;
/**
* Function:函数式接口,有一个输入参数,有一个输出
* 只要是 函数型接口,可以用lambda简化
*/
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 function = (str) -> {return str;};
System.out.println(function.apply("123"));
}
}
断定型接口:有一个输入参数,返回值只能是 布尔值!
package com.swan.function;
import java.util.function.Predicate;
/**
* 断定型接口:有一个输入参数,返回值只能是 布尔值!
*/
public class PredicateDemo {
public static void main(String[] args) {
//判断字符串是否为空
// Predicate predicate = new Predicate() {
// @Override
// public boolean test(String str) {
// return str.isEmpty();
// }
// };
Predicate<String> predicate = str -> str.isEmpty();
System.out.println(predicate.test("123"));
}
}
package com.swan.function;
import java.util.function.Consumer;
/**
* Consumer 消费型接口:只有输入,没有返回值
*/
public class ConsumerDemo {
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("123");
}
}
Supplier:没有参数,只有返回值
package com.swan.function;
import java.util.function.Supplier;
/**
* Supplier:没有参数,只有返回值
*/
public class SupplierDemo {
public static void main(String[] args) {
// Supplier supplier = new Supplier() {
// @Override
// public String get() {
// return "123";
// }
// };
Supplier<String> supplier = () -> "123";
System.out.println(supplier.get());
}
}
什么是Stream 流式计算
大数据:存储 + 计算
存储:集合、MySQL 本质就是存储东西的
计算都应该交给流来操作!
package com.swan.stream;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Locale;
/**
* 题目要求:一分钟内完成此题,只能用一行代码来实现
* 现在有五个用户!筛选
* 1 ID必须是偶数
* 2 年龄必须大于23岁
* 3 用户名转为大写字母
* 4 用户名字母倒着排序
* 5 只输出一个用户
*/
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(5,"e",25);
User u6 = new User(6,"f",26);
// 集合就是存储
List<User> list = Arrays.asList(u1, u2, u3, u4, u5, u6);
// 计算交给流
//lambda表达式、链式编程、函数式接口、Stream流式计算
list.stream()
.filter(u ->{ return u.getId() % 2 == 0;})
.filter(user -> user.getAge() > 23)
.map(user -> user.getName().toUpperCase(Locale.ROOT))
.sorted(Comparator.reverseOrder())
.limit(1)
.forEach(System.out::println);
}
}
什么是 ForkJoin
ForkJoin在jdk1.7,并行执行任务!提高效率。大数据量!
ForkJoin 特定:工作窃取
ForkJoin 的操作
package com.swan.forkjoin;
import java.util.concurrent.RecursiveTask;
/**
* 求和计算
* // 如何使用ForkJoin
* 1 ForkJoinPool 通过它来执行
* 2 计算任务:execute(ForkJoinTask)
* 3 计算类要继承 ForkJoinTask
*/
public class ForkJoinDemo extends RecursiveTask<Long> {
private long start;
private long end;
//临界值
private long temp = 10000L;
public ForkJoinDemo(long start, long end) {
this.start = start;
this.end = end;
}
@Override
protected Long compute() {
if (end - start < temp){
long sum = 0;
for (long i = start; i < end; i++) {
sum += i;
}
return sum;
} else {
//走分支合并计算,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();
return task1.join() + task2.join();
}
}
}
package com.swan.forkjoin;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;
/**
* @ClassName Test
* @Description
* @Author qzl
* @Date 2021/8/25 9:34 下午
**/
public class Test {
public static void main(String[] args) throws ExecutionException, InterruptedException {
// test1(); // 527
// test2(); // 538
test3(); //399
}
// 普通程序员
public static void test1(){
long sum = 0;
Long start = System.currentTimeMillis();
for (long i = 0; i < 10_0000_0000; i++) {
sum += i;
}
long end = System.currentTimeMillis();
System.out.println("sum="+sum+" =>时间:"+(end - start));
}
//会使用forkjoin
public static void test2() throws ExecutionException, InterruptedException{
Long start = System.currentTimeMillis();
ForkJoinPool forkJoinPool = new ForkJoinPool();
ForkJoinTask<Long> task = new ForkJoinDemo(0L,10_0000_0000);
ForkJoinTask<Long> submit = forkJoinPool.submit(task);
Long sum = submit.get();
long end = System.currentTimeMillis();
System.out.println("sum="+sum+" 时间:"+(end - start));
}
//使用 stream 并行流
public static void test3() {
Long start = System.currentTimeMillis();
Long sum = LongStream.rangeClosed(0L,10_0000_0000).parallel().reduce(0,Long::sum);
long end = System.currentTimeMillis();
System.out.println("sum="+sum+" 时间:"+(end - start));
}
}
Future 设计的初衷:对将来的某个事件的结果进行建模
package com.swan.future;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
/**
* 异步调用
*/
public class FutureDemo {
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 completableFuture = CompletableFuture.runAsync(()->{
// try {
// TimeUnit.SECONDS.sleep(2);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
// System.out.println(Thread.currentThread().getName()+"runAsync");
// });
// completableFuture.get(); //获取阻塞执行结果
//有返回值的 supplyAsync 异步回调
CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread().getName()+"supplyAsync");
int i = 1/0;
return 1024;
});
completableFuture.whenComplete((t,u)->{
//编译通过
System.out.println("t=>"+t); // 正常的返回结果
System.out.println("u=>"+u); //返回过来的错误信息
}).exceptionally((e)->{
System.out.println(e.getMessage());
return 233; // 可以获取到错误的返回结果
}).get();
}
}
Volatile 的理解
Volatile 是 java 虚拟机提供的 轻量级的同步机制
什么是 JMM
JMM:java内存模型,不存在的东西,概念!约定!
关于JMM的一些同步的约定:
线程 工作内存、主内存
8种操作
内存交互操作有8种,虚拟机实现必须保证每一个操作都是原子的,不可在分的(对于double和long类型的变量来说,load、store、read和write操作在某些平台上允许例外)
JMM对这八种指令的使用,制定了如下规则:
保证可见性
package com.swan.tvolatile;
import java.util.concurrent.TimeUnit;
public class VolatileDemo {
//如果不加volatile,程序就会死循环
//加 volatile 可以保证可见性
private volatile static int num = 0;
public static void main(String[] args) throws InterruptedException { //main
new Thread(()->{ // 线程1,对主内存的变化是不知道的
while (num == 0){
}
}).start();
TimeUnit.SECONDS.sleep(1);
num = 1;
System.out.println(num);
}
}
不保证原子性
原子性:不可分割
package com.swan.tvolatile;
/**
* 测试不保证原子性
*/
public class VolatileDemo2 {
// 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 num结果为 2 万
for (int i = 0; i < 20; i++) {
new Thread(()->{
for (int j = 0; j <1000; j++) {
add();
}
},String.valueOf(i)).start();
}
while (Thread.activeCount() > 2){
Thread.yield();
}
System.out.println(Thread.currentThread().getName() + " "+num);
}
}
如果不加 Lock
和 synchronized
,怎么保证原子性
使用原子类,解决原子性问题
package com.swan.tvolatile;
import java.util.concurrent.atomic.AtomicInteger;
/**
* 测试不保证原子性
*/
public class VolatileDemo2 {
// volatile 不保证原子性
//原子类的 integer
private volatile static AtomicInteger num = new AtomicInteger();
public static void add(){
//num++; // 不是一个原子操作
num.getAndIncrement(); //AtomicInteger + 1 方法 CAS
}
public static void main(String[] args) {
//理论上 num结果为 2 万
for (int i = 0; i < 20; i++) {
new Thread(()->{
for (int j = 0; j <1000; j++) {
add();
}
},String.valueOf(i)).start();
}
while (Thread.activeCount() > 2){
Thread.yield();
}
System.out.println(Thread.currentThread().getName() + " "+num);
}
}
这些类的底层都直接和操作系统挂钩!在内存中修改值!Unsafe类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那样去执行的。
源代码 -> 编译器优化重排 -> 指令并行也可能会重排 -> 内存系统也会重排 -> 执行
volatile可以避免指令重排
内存屏障,CPU指令。作用:
饿汉式 DCL懒汉式,深究
饿汉式
package com.swan.single;
/**
* 饿汉式单例
*/
public class Hungary {
private Hungary(){}
private final static Hungary HUNGARY = new Hungary();
public static Hungary getInstance(){
return HUNGARY;
}
}
DCL懒汉式
package com.swan.single;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
/**
* 懒汉式
* 道高一尺,魔高一丈
*/
public class LazyMan {
private static boolean qinjiang = false;
private LazyMan(){
synchronized (LazyMan.class){
if (!qinjiang){
qinjiang = true;
} else {
throw new RuntimeException("不要试图使用反射破坏异常");
}
}
System.out.println(Thread.currentThread().getName()+"oks");
};
private volatile static LazyMan lazyMan;
//双重检测锁模式 懒汉式单例 DCL懒汉式
public static LazyMan getInstance(){
//加锁
if (lazyMan == null){
synchronized (LazyMan.class){
if (lazyMan == null){
lazyMan = new LazyMan(); // 不是一个原子操作
/**
* 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;
}
//反射
public static void main(String[] args) throws Exception {
// LazyMan instance = LazyMan.getInstance();
Field qinjiang = LazyMan.class.getDeclaredField("qinjiang");
qinjiang.setAccessible(true);
//获取空参构造器
Constructor<LazyMan> constructor = LazyMan.class.getDeclaredConstructor(null);
constructor.setAccessible(true);// 无视私有构造器
LazyMan instance = constructor.newInstance();
qinjiang.set(instance,false);
LazyMan instance2 = constructor.newInstance();
System.out.println(instance);
System.out.println(instance2);
}
}
静态内部类实现
package com.swan.single;
/**
* 静态内部类实现
*/
public class Holder {
private Holder(){}
public static Holder getInstance(){
return InnerClass.HOLDER;
}
public static class InnerClass{
private static final Holder HOLDER = new Holder();
}
}
单例不安全,因为有反射
枚举实现(解决了反射的问题)
package com.swan.single;
import java.lang.reflect.Constructor;
/**
* enum: 本身也是一个class类
*/
public enum EnumSingle {
INSANCE;
public EnumSingle getInsance(){
return INSANCE;
}
}
class Test{
public static void main(String[] args) throws Exception {
EnumSingle instance = EnumSingle.INSANCE;
Constructor<EnumSingle> declaredConstructor = EnumSingle.class.getDeclaredConstructor(String.class,int.class);
declaredConstructor.setAccessible(true);// 无视私有构造方法
EnumSingle instance2 = declaredConstructor.newInstance();
System.out.println(instance);
System.out.println(instance2);
}
}
枚举类型的最终反编译是有个两个参数的构造方法!
什么是CAS
大厂必须要深入研究底层!有所突破!
CAS 是CPU的并发原语
package com.swan.cas;
import java.util.concurrent.atomic.AtomicInteger;
public class CASDemo {
// CAS compareAndSet: 比较并交换
public static void main(String[] args) {
AtomicInteger atomicInteger = new AtomicInteger(2020);
//expect 期望、update 更新
//public final boolean compareAndSet(int expect, int update)
// 如果我期望的值达到了,那么就更新,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());
System.out.println(atomicInteger.compareAndSet(2020, 2021));
System.out.println(atomicInteger.get());
}
}
Unsafe 类
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:
CAS: ABA问题(狸猫换太子)
package com.swan.cas;
import java.util.concurrent.atomic.AtomicInteger;
public class CASDemo {
// CAS compareAndSet: 比较并交换
public static void main(String[] args) {
AtomicInteger atomicInteger = new AtomicInteger(2020);
//expect 期望、update 更新
//public final boolean compareAndSet(int expect, int update)
// 如果我期望的值达到了,那么就更新,否则,就不更新,CAS 是CPU的并发原语
//=======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());
//==============期望的线程==================================
System.out.println(atomicInteger.compareAndSet(2020, 2021));
System.out.println(atomicInteger.get());
}
}
解决ABA问题
带版本号的原子操作
Integer 使用了对象缓存机制,默认范围是-128~127,推荐使用静态工厂方法valueOf获取对象实例,而不是new 因为valueof使用缓存,而new一定会创建新的对象的内存空间;
package com.swan.cas;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicStampedReference;
public class CASDemo {
// CAS compareAndSet: 比较并交换
public static void main(String[] args) {
// AtomicInteger atomicInteger = new AtomicInteger(2020);
//AtomicStampedReference 注意:如果泛型是一个包装类,注意对象的引用问题
AtomicStampedReference<Integer> atomicStampedReference = new AtomicStampedReference<>(1,1);
new Thread(()->{
int stamp = atomicStampedReference.getStamp();//获得版本号
System.out.println("a1=>"+stamp);
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(atomicStampedReference.compareAndSet(1, 2,
atomicStampedReference.getStamp(), atomicStampedReference.getStamp() + 1));
System.out.println("a2=>"+atomicStampedReference.getStamp());
System.out.println(atomicStampedReference.compareAndSet(2, 1,
atomicStampedReference.getStamp(), atomicStampedReference.getStamp() + 1));
System.out.println("a3=>"+atomicStampedReference.getStamp());
},"A").start();
new Thread(()->{
int stamp = atomicStampedReference.getStamp();//获得版本号
System.out.println("b1=>"+stamp);
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
atomicStampedReference.compareAndSet(1,6,stamp,stamp+1);
System.out.println("b2=>"+atomicStampedReference.getStamp());
},"B").start();
}
}
公平锁:非常公平,不能插队,必须先来后到!
非公平锁:非常不公平,可以插队
public ReentrantLock() {
sync = new NonfairSync();
}
public ReentrantLock(boolean fair) {
sync = fair ? new FairSync() : new NonfairSync();
}
Synchronized 版
package com.haust.lock;
// Synchronized
public class Demo01 {
public static void main(String[] args) {
Phone phone = new Phone();
new Thread(()->{
phone.sms();
},"A").start();
new Thread(()->{
phone.sms();
},"B").start();
}
}
class Phone{
public synchronized void sms(){
System.out.println(Thread.currentThread().getName()
+ "sms");
call(); // 这里也有锁(sms锁 里面的call锁)
}
public synchronized void call(){
System.out.println(Thread.currentThread().getName()
+ "call");
}
}
Lock 版
package com.haust.lock;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Demo02 {
public static void main(String[] args) {
Phone2 phone = new Phone2();
new Thread(()->{
phone.sms();
},"A").start();
new Thread(()->{
phone.sms();
},"B").start();
}
}
class Phone2{
Lock lock = new ReentrantLock();
public void sms(){
lock.lock();
// 细节问题:lock.lock(); lock.unlock();
// lock 锁必须配对,否则就会死在里面
// 两个lock() 就需要两次解锁
lock.lock();
try {
System.out.println(Thread.currentThread().getName()
+ "sms");
call(); // 这里也有锁
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
lock.unlock();
}
}
public void call(){
lock.lock();
try {
System.out.println(Thread.currentThread().getName()
+ "call");
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
package com.haust.lock;
import java.util.concurrent.atomic.AtomicReference;
/**
* 自旋锁
*/
public class SpinlockDemo {
// int 0
// Thread null
// 原子引用
AtomicReference<Thread> atomicReference =
new AtomicReference<>();
// 加锁
public void myLock(){
Thread thread = Thread.currentThread();
System.out.println(Thread.currentThread().getName()
+ "==> mylock");
// 自旋锁
while (!atomicReference.compareAndSet(null,thread)){
}
}
// 解锁
// 加锁
public void myUnLock(){
Thread thread = Thread.currentThread();
System.out.println(Thread.currentThread().getName()
+ "==> myUnlock");
atomicReference.compareAndSet(thread,null);// 解锁
}
}
测试
package com.haust.lock;
import java.util.concurrent.TimeUnit;
public class TestSpinLock {
public static void main(String[] args) throws
InterruptedException {
// ReentrantLock reentrantLock = new ReentrantLock();
// reentrantLock.lock();
// reentrantLock.unlock();
// 底层使用的自旋锁CAS
SpinlockDemo lock = new SpinlockDemo();// 定义锁
new Thread(()-> {
lock.myLock();// 加锁
try {
TimeUnit.SECONDS.sleep(5);
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.myUnLock();// 解锁
}
},"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();
}
}
死锁是什么?
package com.cjg.lock;
import java.util.concurrent.TimeUnit;
public class deadLock {
public static void main(String[] args) {
dead dead = new dead("a", "b");
dead dead1 = new dead("b", "a");
new Thread(dead).start();
new Thread(dead1).start();
}
}
class dead implements Runnable{
private String a;
private String b;
public dead(String a, String b){
this.a=a;
this.b=b;
}
@Override
public void run() {
synchronized (a){
System.out.println(a+"==>"+b);
try {
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (b){
}
}
}
}
第一步 jps -l 找出 问题提的进程
第二步 jstack 加线程号
看日志
看堆栈信息
https://gitee.com/qiangzhouliang_admin/juc