Java学习个人备忘录之线程间的通信
线程间通讯
多个线程在处理同一资源,但是任务却不同.
多个线程在处理同一资源,但是任务却不同.
class Resource
{
String name;
String sex;
}
//输入
class Input implements Runnable
{
Resource r;
Input(Resource r)
{
this.r = r;
}
public void run()
{
int i = 0;
while(true)
{
synchronized(r) //保证两个线程用同一个锁
{
if (i==0)
{
r.name = "mike";
r.sex = "nan";
}
else
{
r.name = "丽丽";
r.name = "女女女女女女女女女";
}
x = (x+1)%2;
}
}
}
}
//输出
class Output implements Runnable
{
Resource r;
Output(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
synchronized(r) //保证两个线程用同一个锁
{
System.out.println(r.name+"....."+r.sex);
}
}
}
}
class ResourceDemo
{
public static void main(String[] args)
{
//创建资源
Resource r = new Resource();
//创建任务
Input in = new Input(r);
Output out = new Output(r);
//创建线程
Thread t1 = new Thread(in);
Thread t2 = new Thread(out);
//开启线程
t1.start();
t2.start();
}
}
但是这样会造成大量的才重复, 没有交替性。
等待唤醒机制
涉及的方法:
1. wait(): 让线程处于冻结状态, 被wait的线程会被存储到线程池中.
2. notify(): 唤醒线程池中一个线程(任意)
3. notifyAll(): 唤醒线程池中的所有线程.
这些方法都必须定义在同步中,
因为这些方法都是用于操做线程状态的方法.
必须要明确到底操做的是哪个锁上的线程.
为什么操做线程的方法wait notify notifyAll定义在了Object类中.
因为这些方法时监视器的方法, 坚持其其实就是锁.
锁可以是任意的对象,任意的对象调用的方式一定定义在Object类中的.
class Resource
{
String name;
String sex;
boolean flag = false;
}
//输入
class Input implements Runnable
{
Resource r;
Input(Resource r)
{
this.r = r;
}
public void run()
{
int i = 0;
while(true)
{
synchronized(r) //保证两个线程用同一个锁
{
if (r.flag)
{
r.wait();
}
if (i==0)
{
r.name = "mike";
r.sex = "nan";
}
else
{
r.name = "丽丽";
r.name = "女女女女女女女女女";
}
r.flag = true;
r.notify(); //唤醒对方
x = (x+1)%2;
}
}
}
}
//输出
class Output implements Runnable
{
Resource r;
Output(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
synchronized(r) //保证两个线程用同一个锁
{
if (!r.flag)
{
r.wait();
}
System.out.println(r.name+"....."+r.sex);
r.flag = false;
r.notify(); //唤醒对方
}
}
}
}
class ResourceDemo2
{
public static void main(String[] args)
{
//创建资源
Resource r = new Resource();
//创建任务
Input in = new Input(r);
Output out = new Output(r);
//创建线程
Thread t1 = new Thread(in);
Thread t2 = new Thread(out);
//开启线程
t1.start();
t2.start();
}
}
上面代码的优化
class Resource
{
private String name; //这里要私有化
private String sex;
boolean flag = false;
public synchronized void set(String name,String sex) //对数据要可控化
{
if (this.flag)
try{this.wait();}catch(InterruptedException e){}
this.name = name;
this.sex = sex;
flag = true;
this.notify();
}
public synchronized void out()
{
if (this.flag)
try{this.wait();}catch(InterruptedException e){}
System.out.println(name+"....."+sex);
flag = false;
this.notify();
}
}
//输入
class Input implements Runnable
{
Resource r;
Input(Resource r)
{
this.r = r;
}
public void run()
{
int i = 0;
while(true)
{
if (i==0)
{
r.set("mike","nan");
}
else
{
r.set"丽丽","女女女女女女女女女");
}
x = (x+1)%2;
}
}
}
//输出
class Output implements Runnable
{
Resource r;
Output(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
r.out();
}
}
}
class ResourceDemo3
{
public static void main(String[] args)
{
//创建资源
Resource r = new Resource();
//创建任务
Input in = new Input(r);
Output out = new Output(r);
//创建线程
Thread t1 = new Thread(in);
Thread t2 = new Thread(out);
//开启线程
t1.start();
t2.start();
}
}
多生产者多消费者问题
class Resource
{
private String name;
private int count = 1;
private boolean flag = false;
public synchronized void set(String name)
{
if (flag)
try{this.wait();}catch(InterruptedException e){}
this.name = name + count;
count++;
System.out.println(Thread.currentThread().getName()+".....生产者....."+this.name);
flag = true;
notify();
}
public synchronized void out()
{
if (!flag)
try{this.wait();}catch(InterruptedException e){}
System.out.println(Thread.currentThread().getName()+".....消费者....."+this.name);
flag = false;
notify();
}
}
class Producer implements Runnable
{
private Resource r;
Producer(Resource r)
{
this.r = r;
}
public void run()
{
while (true)
{
r.set("烤鸭");
}
}
}
class Consumer implements Runnable
{
private Resource r;
Consumer(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
r.out();
}
}
}
class ProducerConsumerDemo
{
public static void main(String[] args)
{
Resource r = new Resource();
Producer pro = new Producer(r);
Consumer con = new Consumer(r);
Thread t0 = new Thread(pro);
Thread t1 = new Thread(pro);
Thread t2 = new Thread(con);
Thread t3 = new Thread(con);
t0.start();
t1.start();
t2.start();
t3.start();
}
}
但是这样会出现安全隐患, 从这4个线程上看, 一共分了两组, t0和t1一组, t2和t3一组, 当t1 t2 t3 睡眠时, t0出来后再次唤醒t1, 这时t1是不用判断的if条件的,直接向下继续执行. 这样就又进行了"生产烤鸭", 所以出现了安全隐患. 解决办法: 将两个if 换成 while, 这样在t1醒来的时候会继续判断flag是否为真. 但是这样又会出现死锁现象, 因为t1判断flag时, flag为真, 这时t1会再次等待,这时4个线程都进入等待状态---死锁!!
解决办法1
将notify换成notifyAll, 这样就一定会唤醒对方的线程,同时自己方的线程因为while循环出不去.
class Resource
{
private String name;
private int count = 1;
private boolean flag = false;
public synchronized void set(String name)
{
while (flag)
try{this.wait();}catch(InterruptedException e){}
this.name = name + count;
count++;
System.out.println(Thread.currentThread().getName()+".....生产者....."+this.name);
flag = true;
notifyAll();
}
public synchronized void out()
{
while (!flag)
try{this.wait();}catch(InterruptedException e){}
System.out.println(Thread.currentThread().getName()+".....消费者....."+this.name);
flag = false;
notifyAll();
}
}
class Producer implements Runnable
{
private Resource r;
Producer(Resource r)
{
this.r = r;
}
public void run()
{
while (true)
{
r.set("烤鸭");
}
}
}
class Consumer implements Runnable
{
private Resource r;
Consumer(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
r.out();
}
}
}
class ProducerConsumerDemo
{
public static void main(String[] args)
{
Resource r = new Resource();
Producer pro = new Producer(r);
Consumer con = new Consumer(r);
Thread t0 = new Thread(pro);
Thread t1 = new Thread(pro);
Thread t2 = new Thread(con);
Thread t3 = new Thread(con);
t0.start();
t1.start();
t2.start();
t3.start();
}
}
if判断标记只有一次, 会导致不该运行的线程运行了, 出现了数据错误的情况. while判断标记, 解决了线程获取执行权后, 是否要运行。
notify: 只能唤醒一个线程, 如果本方唤醒了本方, 就没有意义, 而且while判断标记notify会导致死锁. notifyAll解决了, 本方线程一定会唤醒对方线程.
解决办法2:
JDK1.5新特征的解决办法--Lock
可以看出来, 上面的解决方法会造成多次无用的判断, 这会降低效率,可以用这面的方法解决.
Lock l = new ReentrantLock();
void show()
{
l.lock(); //获取锁
code...
l.unlock(); //释放锁
}
jdk1.5以后将同步和锁封装成了对象.
并将操作锁的隐式方法定义到了该对象中,
将隐式动作变成了显示动作.
但是如果执行的代码抛出了异常, 这样代码就会一直持有锁,不释放,所以要如下
Lock l = new ReentrantLock();
void show()
{
l.lock(); //获取锁
try
{
code...
}
finally
{
l.unlock(); //释放锁
}
}
import java.util.concurrent.locks.*
class Resource
{
private String name;
private int count = 1;
private boolean flag = false;
Lock l = new ReentrantLock();//因为Lock是java.util.concurrent.locks包中的类, 所以要先导入包.
public void set(String name) //这里的同步就可以去掉了
{
l.lock(); //在这里加上锁
try
{
while (flag)
try{this.wait();}catch(InterruptedException e){}
this.name = name + count;
count++;
System.out.println(Thread.currentThread().getName()+".....生产者....."+this.name);
flag = true;
notifyAll();
}
finally
{
l.unlock();
}
}
public void out()
{
l.lock();
try
{
while (!flag)
try{this.wait();}catch(InterruptedException e){}
System.out.println(Thread.currentThread().getName()+".....消费者....."+this.name);
flag = false;
notifyAll();
}
finally
{
l.unlock();
}
}
}
class Producer implements Runnable
{
private Resource r;
Producer(Resource r)
{
this.r = r;
}
public void run()
{
while (true)
{
r.set("烤鸭");
}
}
}
class Consumer implements Runnable
{
private Resource r;
Consumer(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
r.out();
}
}
}
class ProducerConsumerDemo
{
public static void main(String[] args)
{
Resource r = new Resource();
Producer pro = new Producer(r);
Consumer con = new Consumer(r);
Thread t0 = new Thread(pro);
Thread t1 = new Thread(pro);
Thread t2 = new Thread(con);
Thread t3 = new Thread(con);
t0.start();
t1.start();
t2.start();
t3.start();
}
}
解决办法3:
JDK1.5新特征的解决办法--Condition
Condition在底层上是这样实现的:
interface Condition
{
await();
signal();
signalAll();
}
所以要这样实现, 如下:
Lock l = new ReectrantLock();
Condition c1 = l.newCondition();
Condition c2 = l.newCondition();
import java.util.concurrent.locks.*
class Resource
{
private String name;
private int count = 1;
private boolean flag = false;
//创建一个锁对象.
Lock l = new ReentrantLock();//因为Lock是java.util.concurrent.locks包中的类, 所以要先导入包.
//通过已有的锁获取该锁上的监视器对象.
Condition con = l.newCondition();
public void set(String name) //这里的同步就可以去掉了
{
l.lock(); //在这里加上锁
try
{
while (flag)
// try{this.wait();}catch(InterruptedException e){} //这里用con.await()替换
try{con.await();}catch(InterruptedException e){}
this.name = name + count;
count++;
System.out.println(Thread.currentThread().getName()+".....生产者....."+this.name);
flag = true;
// notifyAll(); //这里用con.signalAll() 替换
con.signalAll();
}
finally
{
l.unlock();
}
}
public void out()
{
l.lock();
try
{
while (!flag)
// try{this.wait();}catch(InterruptedException e){} //这里用con.await()替换
try{con.await();}catch(InterruptedException e){}
System.out.println(Thread.currentThread().getName()+".....消费者....."+this.name);
flag = false;
// notifyAll(); //这里用con.signalAll() 替换
con.signalAll();
}
finally
{
l.unlock();
}
}
}
class Producer implements Runnable
{
private Resource r;
Producer(Resource r)
{
this.r = r;
}
public void run()
{
while (true)
{
r.set("烤鸭");
}
}
}
class Consumer implements Runnable
{
private Resource r;
Consumer(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
r.out();
}
}
}
class ProducerConsumerDemo2
{
public static void main(String[] args)
{
Resource r = new Resource();
Producer pro = new Producer(r);
Consumer con = new Consumer(r);
Thread t0 = new Thread(pro);
Thread t1 = new Thread(pro);
Thread t2 = new Thread(con);
Thread t3 = new Thread(con);
t0.start();
t1.start();
t2.start();
t3.start();
}
}
其实解决办法3和解决办法2没有太大的区别.并没有真的运用了1.5的新特征。
解决办法4
这个解决办法才真正的运用到了1.5的新特征。
import java.util.concurrent.locks.*
class Resource
{
private String name;
private int count = 1;
private boolean flag = false;
//创建一个锁对象.
Lock l = new ReentrantLock();//因为Lock是java.util.concurrent.locks包中的类, 所以要先导入包.
//通过已有的锁获取该锁上的监视器对象.
// Condition con = l.newCondition();
//通过已有的锁获取两组监视器, 一组监视生产者, 一组监视消费者.
Condition producer_con = l.newCondition();
Condition consumer_con = l.newCondition();
public void set(String name) //这里的同步就可以去掉了
{
l.lock(); //在这里加上锁
try
{
while (flag)
try{producer_con.await();}catch(InterruptedException e){} //这里只让生产者等待
this.name = name + count;
count++;
System.out.println(Thread.currentThread().getName()+".....生产者....."+this.name);
flag = true;
consumer_con.signal(); //这里直接唤醒消费者
}
finally
{
l.unlock();
}
}
public void out()
{
l.lock();
try
{
while (!flag)
try{consumer_con.await();}catch(InterruptedException e){} //这里只让消费者等待
System.out.println(Thread.currentThread().getName()+".....消费者....."+this.name);
flag = false;
producer_con.signalAll(); //这里只唤醒生产者
}
finally
{
l.unlock();
}
}
}
class Producer implements Runnable
{
private Resource r;
Producer(Resource r)
{
this.r = r;
}
public void run()
{
while (true)
{
r.set("烤鸭");
}
}
}
class Consumer implements Runnable
{
private Resource r;
Consumer(Resource r)
{
this.r = r;
}
public void run()
{
while(true)
{
r.out();
}
}
}
class ProducerConsumerDemo2
{
public static void main(String[] args)
{
Resource r = new Resource();
Producer pro = new Producer(r);
Consumer con = new Consumer(r);
Thread t0 = new Thread(pro);
Thread t1 = new Thread(pro);
Thread t2 = new Thread(con);
Thread t3 = new Thread(con);
t0.start();
t1.start();
t2.start();
t3.start();
}
}
