467 lines
13 KiB
Markdown
467 lines
13 KiB
Markdown
# 线程
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## 进程和线程
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### 进程介绍：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251226170135578.png" alt="image-20251226170130636" style="zoom:50%;" />
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### 线程Thread介绍：
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进程可以同时执行多个任务，每个任务就是线程：
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### 多线程的作用：
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提升执行效率，使更多进程可以并行执行
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服务器必须用多线程
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## Java中开启线程的方式：
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### 1:继承Thread类：
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案例：
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```Java
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public static void main(String[] args) {
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/*
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* 继承Thread类
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* 重写run方法
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* 将线程任务代码写在run方法
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* 创建对象
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* 对象名.start开启线程
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* 只有调用start方法才会开启一个新线程
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*/
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Demo d1 = new Demo();
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Demo d2 = new Demo();
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d1.start();
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d2.start();
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}
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}
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class Demo extends Thread {
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@Override
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public void run() {
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for (int i = 1; i <= 200; i++) {
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System.out.println("打印了" + i);
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}
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}
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}
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```
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### 注意：
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### 2：实现Runnable接口
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```java
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/*
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方法2 实现runnable接口
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编写一个类实现接口
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重写run方法
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创建线程任务资源（就是创建对象）
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然后创建线程对象，将任务资源传入，走构造方法
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使用线程对象调用start方法
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*/
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public static void main(String[] args) {
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MyRunnable mr = new MyRunnable();
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Thread tr = new Thread(mr);
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tr.start();
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}
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}
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class MyRunnable implements Runnable{
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@Override
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public void run() {
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System.out.println("八奈见杏菜");
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}
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}
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```
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### 3：实现Callable接口(有结果返回)
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```java
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public class ThreadDemo3 {
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public static void main(String[] args) throws Exception {
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/*
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创建一个类实现Callable接口
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重写call方法
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创建线程任务资源对象
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创建线程任务对象，封装线程任务资源（FutureTask）
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创建线程对象传入线程任务
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使用线程对象调用start方法开启线程
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*/
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MyCallAble mc = new MyCallAble();
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FutureTask<Integer> ft = new FutureTask<>(mc);
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Thread t = new Thread(ft);
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t.start();
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Integer result = ft.get();
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System.out.println(result);
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}
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}
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class MyCallAble implements Callable<Integer>{
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@Override
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public Integer call() throws Exception {
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int sum = 0;
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for (int i = 1; i <= 100; i++) {
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sum += i;
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}
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return sum;
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}
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}
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```
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### 尽量选择后两个，拓展性更好
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## 线程的方法
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### 名字相关：
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### 休眠线程：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251226195658228.png" alt="image-20251226195657226" style="zoom: 67%;" />
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### 线程调度方法：
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Java是抢占式调度
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251226200312037.png" alt="image-20251226200310813" style="zoom:67%;" />
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### 守护线程
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`final void setDaemon(boolean on );`
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251226200638217.png" alt="image-20251226200636908" style="zoom: 67%;" />
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如图代码所示，t2守护t1，t1线程任务结束，t2也结束(不是立刻结束，t2会在苟活一会儿)
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哪个线程对象调用setDaemon方法，这个线程就是守护线程
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## 线程的安全与同步
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251227180107783.png" alt="image-20251227180059497" style="zoom: 50%;" />
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### 1.同步代码块：
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**使用同步代码块指定锁对象时，用类的字节码对象**
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**共享数据要用static修饰**
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### 2.同步方法：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251227182958488.png" alt="image-20251227182957021" style="zoom: 67%;" />
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### 3.Lock锁：
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```Java
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public static void main(String[] args) {
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TicketShop1 ts = new TicketShop1();
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Thread t1 = new Thread(ts);
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Thread t2 = new Thread(ts);
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Thread t3 = new Thread(ts);
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t1.start();
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t2.start();
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t3.start();
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}
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}
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class TicketShop1 implements Runnable{
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private int ticket = 100;
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private ReentrantLock lock = new ReentrantLock();
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@Override
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public void run() {
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while (true){
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//上锁
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try {
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lock.lock();
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if (ticket == 0){
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break;
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}
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System.out.println("卖出了"+ticket+"号票");
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ticket--;
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} finally {
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//记得关闭锁
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lock.unlock();
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}
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}
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}
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}
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```
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附加知识点：死锁：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251227184708459.png" alt="image-20251227184706346" style="zoom:50%;" />
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## 线程通信
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228190237885.png" alt="image-20251228190234137" style="zoom:50%;" />
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### 两条线程交替执行案例：
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```Java
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public static void main(String[] args) {
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Print p = new Print();
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Thread t1= new Thread(new Runnable() {
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@Override
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public void run() {
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while (true) {
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synchronized (Print.class) {
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try {
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p.print1();
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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}
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}
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});
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t1.start();
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Thread t2 = new Thread(new Runnable() {
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@Override
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public void run() {
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while (true) {
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synchronized (Print.class) {
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try {
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p.print2();
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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}
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}
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});
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t2.start();
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}
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}
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class Print{
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private int flag = 1;
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public void print1() throws InterruptedException {
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if (flag != 1){
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//wait只能通过锁对象进行调用
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Print.class.wait();
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}
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System.out.print("八");
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System.out.print("奈");
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System.out.print("见");
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System.out.print("杏");
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System.out.print("菜");
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System.out.println();
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flag = 2;
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//notif拥有空唤醒的权利
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Print.class.notify();
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}
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public void print2() throws InterruptedException {
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if (flag != 2){
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Print.class.wait();
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}
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System.out.print("温");
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System.out.print("水");
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System.out.print("佳");
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System.out.print("树");
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System.out.println();
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flag = 1;
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Print.class.notify();
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}
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}
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```
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### 注意事项：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228190306178.png" alt="image-20251228190304630" style="zoom: 67%;" />
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### 若想提升效率，使用ReentrantLock实现同步，获取Condition对象
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228191731287.png" alt="image-20251228191729896" style="zoom:50%;" />
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注意：第一次指定线程等待时，绑定了线程
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### 三条线程交替执行案例：
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```Java
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public static void main(String[] args) {
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Printer p = new Printer();
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Thread t1= new Thread(new Runnable() {
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@Override
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public void run() {
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while (true) {
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try {
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p.print1();
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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}
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});
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t1.start();
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Thread t2 = new Thread(new Runnable() {
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@Override
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public void run() {
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while (true) {
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try {
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p.print2();
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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}
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});
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t2.start();
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new Thread(new Runnable() {
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@Override
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public void run() {
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while (true) {
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try {
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p.print3();
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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}
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}).start();
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}
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}
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class Printer{
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private int flag = 1;
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ReentrantLock lock = new ReentrantLock();
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//调用newCondition来获取条件对象以此来指定线程
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Condition c1 = lock.newCondition();
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Condition c2 = lock.newCondition();
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Condition c3 = lock.newCondition();
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public void print1() throws InterruptedException {
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lock.lock();
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if (flag != 1){
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//第一次调用await方法时绑定了线程
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c1.await();
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}
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System.out.print("八");
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System.out.print("奈");
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System.out.print("见");
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System.out.print("杏");
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System.out.print("菜");
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System.out.println();
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flag = 2;
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c2.signal();
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lock.unlock();
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}
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public void print2() throws InterruptedException {
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lock.lock();
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if (flag != 2){
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c2.await();
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}
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System.out.print("温");
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System.out.print("水");
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System.out.print("佳");
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System.out.print("树");
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System.out.println();
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flag = 3;
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c3.signal();
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lock.unlock();
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}
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public void print3() throws InterruptedException {
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lock.lock();
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if (flag != 3){
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c3.await();
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}
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System.out.print("温");
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System.out.print("水");
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System.out.print("梦");
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System.out.print("子");
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System.out.println();
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flag = 1;
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c1.signal();
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lock.unlock();
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}
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}
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```
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### 生产者消费者模式：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228193331390.png" alt="image-20251228193330122" style="zoom:50%;" />
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228193430647.png" alt="image-20251228193429569" style="zoom:50%;" />
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### 生产者消费者案例：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228193309975.png" alt="image-20251228193308023" style="zoom:67%;" />
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## 线程生命周期：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228194047345.png" alt="image-20251228194046082" style="zoom:67%;" />
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## 线程池：
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重点：自定义线程池
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228200136901.png" alt="image-20251228200135970" style="zoom:50%;" />
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**拒绝策略**：用的最多的只有第一种AbortPolicy
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**任务队列：**
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228200930260.png" alt="image-20251228200929336" style="zoom: 80%;" />
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### 总结：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228200821304.png" alt="image-20251228200820075" style="zoom:50%;" />
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### 案例：
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```Java
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public class Demo3 {
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public static void main(String[] args) {
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ThreadPoolExecutor tp = new ThreadPoolExecutor(
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3,//核心数
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6,//最大核心数
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10,//空闲时间
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TimeUnit.SECONDS,//时间单位
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new ArrayBlockingQueue<>(10),//排队人数
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Executors.defaultThreadFactory(),//线程对象任务工厂，基本为固定
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new ThreadPoolExecutor.AbortPolicy()//拒绝策略，基本只用这个方法
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);
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for (int i = 1; i <17 ; i++) {
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tp.submit(new Runnable() {
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@Override
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public void run() {
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System.out.println(Thread.currentThread().getName() + "调用了hhh");
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}
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});
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}
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tp.shutdown();
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}
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}
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```
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## 单例设计模式：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228204751280.png" alt="image-20251228204750037" style="zoom:50%;" />
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两种方式：
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**饿汉式：简单不烧脑**：
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直接创建出对象 而不是调用方法的时候再创建对象
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**懒汉式：（延迟加载模式）：**
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251228204928022.png" alt="image-20251228204926855" style="zoom:50%;" /> |