记录面试过程中被问到的几个需要手写代码的小案例
1.请手写出线程的等待唤醒机制
案例中两个线程：SyncSetThread设置学生信息，SyncGetThread用来获取学生信息，在Student实体中提供一个标记属性flag，记录当前是否有数据。
等待唤醒机制
-
设置信息线程SyncSetThread
/*
* 使用Object的wait() 和 notify() 来实现等待唤醒机制
* Created by JackYang on 2017/10/17.
*/
class SyncSetThread implements Runnable {
private final Student student;
SyncSetThread(Student student) {
this.student = student;
}
@Override
public void run() {
int num = 0;
while (true) {
synchronized (student) {
if (student.flag) {
try {
student.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
if (num % 2 == 0) {
student.name = "JackYang";
student.age = 26;
} else {
student.name = "江一燕";
student.age = 28;
}
++num;
student.flag = true;
student.notify();
//此时唤醒，SyncSetThread和SyncGetThread两个线程都有同等的机会去抢占资源
}
}
}
}
-
获取信息线程SyncGetThread
class SyncGetThread implements Runnable {
private final Student student;
SyncGetThread(Student student) {
this.student = student;
}
@Override
public void run() {
while (true) {
synchronized (student) {
if (!student.flag) {
try {
//对象中没有数据的时候就等待
student.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(student.name + "---" + student.age);
//数据消费完了(取出后)改变标记
student.flag = false;
student.notify();
//此时唤醒，SyncSetThread和SyncGetThread两个线程都有同等的机会去抢占资源
}
}
}
}
-
测试入口
/*
* 线程的等待唤醒机制，实现一人一次有规律
* Created by JackYang on 2017/10/17.
*/
public class TestSyncThread {
public static void main(String[] args) {
Student student = new Student();
SyncSetThread syncSetThread = new SyncSetThread(student);
SyncGetThread syncGetThread = new SyncGetThread(student);
Thread thread1 = new Thread(syncSetThread);
Thread thread2 = new Thread(syncGetThread);
thread1.start();
thread2.start();
}
}
2.请手写出线程死锁代码
这个没得商量，直接上代码
/**
* 死锁代码
* Created by JackYang on 2017/10/17.
*/
class DieThread extends Thread {
private boolean flag;
DieThread(boolean flag) {
this.flag = flag;
}
@Override
public void run() {
if (flag) {
//防止一次卡不住
while (true) {
synchronized (MyLock.lockA) {
System.out.println("true lockA");
synchronized (MyLock.lockB) {
System.out.println("true lockB");
}
}
}
} else {
while (true) {
synchronized (MyLock.lockB) {
System.out.println("false lockB");
synchronized (MyLock.lockA) {
System.out.println("false lockA");
}
}
}
}
}
}
