Java多线程-Lock锁的使用，以及生产者和消费者的实现
本文中将主要介绍Java多线程编程基础中的Lock锁对象的使用，以及如何一步一步实现Java代码的生产者与消费者；
1、Java中如何使用Lock锁以及死锁问题的描述
2、Java实现生产者与消费者的过程（一步一步优化的步骤）
1、Java中如何使用Lock锁以及死锁问题的描述
LOCK锁的出现：为了更清晰的表达如何加锁和释放锁，JDK5以后提供了一个新的锁对象LOCK；
Lock锁中最重要的个方法：
void lock()
void unlock()
下面就是Lock锁的一个简单的演示Demo，之后的死锁问题也会使用Lock锁来进行表现；
1）例子一：利用Lock对象实现售票机制：
SellTicket.java
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class SellTicket implements Runnable {
// 定义票
private int tickets = 100;
// 定义锁对象
private Lock lock = new ReentrantLock();
@Override
public void run() {
while (tickets > 0) {
// 之所以不带catch是因为保证在出错的情况下保证锁的释放
try{
// 加锁
lock.lock();
if (tickets > 0) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets-- + "张票" );
}
} finally {
// 释放锁
lock.unlock();
}
}
}
}SellTicketDemo.java
public class SellTicketDemo {
public static void main(String[] args) {
// 创建资源对象
SellTicket st = new SellTicket();
// 创建窗口
Thread thread1 = new Thread(st, "窗口一");
Thread thread2 = new Thread(st, "窗口二");
Thread thread3 = new Thread(st, "窗口三");
// 开启线程
thread1.start();
thread2.start();
thread3.start();
}
}运行效果：
可以看见线程在运行的时候，基本上都是成片运行的，并没有比较好的交叉运行
2）例子二：利用Lock实现死锁机制
MyLock.java
/** * 创建两把锁可以直接调用 * @author YQ * */
public class MyLock {
//创建两把锁对象
public static final Object objA = new Object();
public static final Object objB = new Object();
}DieLock.java
public class DieLock extends Thread {
private boolean flag;
public DieLock(boolean flag) {
this.flag = flag;
}
@Override
public void run() {
if (flag) {
synchronized (MyLock.objA) {
System.out.println("if ObjA");
synchronized (MyLock.objB) {
System.out.println("if ObjB");
}
}
} else {
synchronized (MyLock.objB) {
System.out.println("else ObjB");
synchronized (MyLock.objA) {
System.out.println("else ObjA");
}
}
}
}
}DieLockDemo.java
/** * 同步的弊端： * A:效率低 * B:容易产生死锁 * 死锁： * 两个或者两个以上的线程在争夺资源的过程中，发生的一种互相等待的现象 * @author YQ */
public class DieLockDemo {
public static void main(String[] args) {
DieLock dieLock1 = new DieLock(true);
DieLock dieLock2 = new DieLock(false);
dieLock1.start();
dieLock2.start();
}
}运行效果：
2、Java实现生产者与消费者的过程（一步一步优化的步骤）
1）初始实现，定义一个Student的JavaBean的类，然后通过set保存Student的数据作为生产者，之后通过get取出Student的数据作为消费者，但是以下的实现仅仅只有一次！
Student.java
public class Student {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Student [name=" + name + ", age=" + age + "]";
}
}SetThread.java
public class SetThread extends Thread{
private Student student;
public SetThread(Student student) {
super();
this.student = student;
}
@Override
public void run() {
student.setName("admin");
student.setAge(24);
}
}GetThread.java
public class GetThread extends Thread {
private Student student;
public GetThread(Student student) {
super();
this.student = student;
}
@Override
public void run() {
System.out.println(student.getName() + "====" + student.getAge());
}
}StudentDemo.java
public class StudentDemo {
public static void main(String[] args) {
// 创建两个线程的共用资源
Student student = new Student();
// 创建生产者和消费者
SetThread thread1 = new SetThread(student);
GetThread thread2 = new GetThread(student);
//开启生产者和消费者线程
thread1.start();
thread2.start();
}
}运行效果：
2）进一步的循环实现多次生产多次消费，使用的是同步的方式
Student.java代码同上！
GetThread.java
public class GetThread extends Thread {
private Student student;
public GetThread(Student student) {
super();
this.student = student;
}
@Override
public void run() {
while (true) {
synchronized (student) {
System.out.println(student.getName() + "====" + student.getAge());
}
}
}
}SetThread.java
public class SetThread extends Thread{
private Student student;
private int x = 0;
public SetThread(Student student) {
super();
this.student = student;
}
@Override
public void run() {
while (true) {
//必须是相同的同一把锁
synchronized (student) {
if (x%2 == 0) {
student.setName("admin");
student.setAge(24);
} else {
student.setName("manager");
student.setAge(28);
}
x++;
}
}
}
}StudentDemo.java
public class StudentDemo {
public static void main(String[] args) {
// 创建两个线程的共用资源
Student student = new Student();
// 创建生产者和消费者
SetThread thread1 = new SetThread(student);
GetThread thread2 = new GetThread(student);
//开启生产者和消费者线程
thread1.start();
thread2.start();
}
}运行效果（停止的时候出现的ad没有完整与线程的实现没有关系，主要是因为命令窗口的缓冲没有完整的原因）：
3）真正实现生产者与消费者：生产者生产后消费者才可以消费，消费者消费之后生产者才可以生产如此往复：
Student.java
public class Student {
private String name;
private int age;
//默认情况下不存在数据
private boolean flag;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public boolean isFlag() {
return flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
@Override
public String toString() {
return "Student [name=" + name + ", age=" + age + "]";
}
}SetThread.java
public class SetThread extends Thread{
private Student student;
private int x = 0;
public SetThread(Student student) {
super();
this.student = student;
}
@Override
public void run() {
while (true) {
// 必须是相同的同一把锁
synchronized (student) {
// 判断
if (student.isFlag()) {
try {
student.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (x%2 == 0) {
student.setName("admin");
student.setAge(24);
} else {
student.setName("manager");
student.setAge(28);
}
x++;
// 修改标记
student.setFlag(true);
student.notify();
}
}
}
}GetThread.java
public class GetThread extends Thread {
private Student student;
public GetThread(Student student) {
super();
this.student = student;
}
@Override
public void run() {
while (true) {
synchronized (student) {
if (!student.isFlag()) {
try {
student.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
System.out.println(student.getName() + "====" + student.getAge());
student.setFlag(false);
student.notify();
}
}
}
}运行效果：
StudentDemo.java
/** * 等待唤醒： * Object类中提供了三个方法： * wait():等待; * notify():唤醒单个线程; * notifyAll():唤醒所有线程; * @author YQ * */
public class StudentDemo {
public static void main(String[] args) {
// 创建两个线程的共用资源
Student student = new Student();
// 创建生产者和消费者
SetThread thread1 = new SetThread(student);
GetThread thread2 = new GetThread(student);
//开启生产者和消费者线程
thread1.start();
thread2.start();
}
}运行效果：
