java多少线程操作共享数据线程安全问题加锁-编程知识

java多少线程操作共享数据线程安全问题加锁

1、有问题的写法
AdminController文件

package com.controller;import com.myThread.AdminThread;
import com.myThread.MyCallable;
import com.myThread.MyRunnable;
import org.springframework.web.bind.annotation.*;import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;@RestController
@CrossOrigin
@RequestMapping("/admin")
public class AdminController{public static int count = 10;@GetMapping("/{id}")public long findById(@PathVariable Long id) throws InterruptedException {AdminThread t1 = new AdminThread();AdminThread t2 = new AdminThread();t1.start();t2.start();return id;}
}

AdminThread文件

package com.myThread;import com.controller.AdminController;public class AdminThread extends Thread{@Overridepublic void run() {while (true){if(AdminController.count == 0){break;}AdminController.count--;System.out.print(getName()+"线程"+AdminController.count+"\n");}}
}

执行结果，可以看到重复执行，不安全
在这里插入图片描述

解决方法加锁
AdminController文件

package com.controller;import com.myThread.AdminThread;
import com.myThread.MyCallable;
import com.myThread.MyRunnable;
import org.springframework.web.bind.annotation.*;import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;@RestController
@CrossOrigin
@RequestMapping("/admin")
public class AdminController{//数量public static int count = 10;//锁对象public static final Object lock = new Object();public static boolean flag = false;@GetMapping("/{id}")public long findById(@PathVariable Long id) throws InterruptedException {AdminThread t1 = new AdminThread();AdminThread t2 = new AdminThread();t1.start();t2.start();return id;}
}

AdminThread文件

package com.myThread;import com.controller.AdminController;public class AdminThread extends Thread{@Overridepublic void run() {while (true){synchronized(AdminController.lock){if(AdminController.count == 0){break;}else{if(!AdminController.flag){//操作AdminController.count--;System.out.print(getName()+"线程"+AdminController.count+"\n");//释放AdminController.lock.notifyAll();}else{//一直循环监听try {AdminController.lock.wait();} catch (InterruptedException e) {e.printStackTrace();}}}}}}
}

AdminThread上面这个！会有空执行（虽然没有错，但多跑了一点点），应该下面这样

package com.myThread;import com.controller.AdminController;public class AdminThread extends Thread{@Overridepublic void run() {while (true){synchronized(AdminController.lock){if(AdminController.count == 0){break;}else{//操作AdminController.count--;System.out.print(getName()+"线程"+AdminController.count+"\n");//释放AdminController.lock.notifyAll();}}}}
}