黑马程序员-----多线程之间的通信（生产者消费者）

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线程间的相互作用：

　　线程间的相互作用：线程之间需要一些协调通信，来共同完成一件任务。
   因为wait和notify方法定义在Object类中，因此会被所有的类所继承。
   这些方法都是final的，即它们都是不能被重写的，不能通过子类覆写去改变它们的行为。

在前面学习了多线程编程中使用同步机制的重要性，并学会了如何实现同步的方法来正确的访问共享资源。这些线程之间的关系是平等的，批次之间并不存在依赖，他们各自竞争CPU的资源，互不相让，并且还无条件的阻止其他线程对共享资源的访问。然而，也有很多现实问题要求不仅仅要同步的访问同一共享资源，而且线程间还彼此牵制，通过相互通信来向前推进。那么，多个线程之间是如何进行通信的呢？

 

线程间的通信其实就是多个线程在操作同一个资源，但操作的动作不同。

class Res {
String name;
String sex;
}

class Input implements Runnable {
private Res r;

public Input(Res r) {
// TODO Auto-generated constructor stub
this.r = r;
}

public void run() {
int x = 0;
while (true) {
if (x == 0) {
r.name = "mike";
r.sex = "man";
} else {
r.name = "丽丽";
r.sex = "女女女";
}
x = ++x % 2;
}
}
}

class Output implements Runnable {
private Res r;

Output(Res r) {
this.r = r;
}

public void run() {
while (true) {
System.out.println(r.name + "----" + r.sex);
}
}
}

public class Communicate {
public static void main(String[] args) {
// TODO Auto-generated method stub
Res r = new Res();
Input in = new Input(r);
Output out = new Output(r);

Thread t1 = new Thread(in);
Thread t2 = new Thread(out);

t1.start();
t2.start();
}
}

但是这样写的会出现名字与性别不相匹配的情况。

这就表明了出现了安全问题，当出现安全问题时就要想到需要同步。

class Res {
String name;
String sex;
}

class Input implements Runnable {
private Res r;
Object obj = new Object();

public Input(Res r) {
// TODO Auto-generated constructor stub
this.r = r;
}

public void run() {
int x = 0;
while (true) {
synchronized (obj) {
if (x == 0) {
r.name = "mike";
r.sex = "man";
} else {
r.name = "丽丽";
r.sex = "女女女";
}
x = ++x % 2;
}
}
}
}

class Output implements Runnable {
private Res r;
Object obj = new Object();
Output(Res r) {
this.r = r;
}

public void run() {
while (true) {
synchronized (obj)
{
System.out.println(r.name + "----" + r.sex);
}
}
}
}

public class Communicate {

public static void main(String[] args) {
// TODO Auto-generated method stub
Res r = new Res();
Input in = new Input(r);
Output out = new Output(r);

Thread t1 = new Thread(in);
Thread t2 = new Thread(out);

t1.start();
t2.start();

}
}

但是这样做之后还是没有解决出现的问题。

那么还是要考虑那两个原则：

1.是否是两个及两个以上的线程？（满足）

2.是否是同一个锁？（？？）

用生产者和消费者的例子来观察同步的效果：

class ConsumeDemo
{
public static void main(String[] args)
{
Resource r = new Resource();
Producer pro = new Producer(r);
Consumer con = new Consumer(r);

Thread t1 = new Thread(pro);
Thread t2 = new Thread(con);

t1.start();
t2.start();
}
}

class Resource
{
private String name;
private int count = 1;
private boolean flag = false;
public synchronized void set (String name)
{
if(flag)
try{wait();}catch(Exception e){}
this.name = name+"--"+count++;
System.out.println(Thread.currentThread().getName()+"..生产者.."+this.name);
flag = true;
this.notify();
}
public synchronized void out()
{
if(!flag)
try{wait();}catch(Exception e){}
System.out.println(Thread.currentThread().getName()+"..消费者.."+this.name);
flag = false;
this.notify();

}
}
class Producer implements Runnable
{
private Resource res;
Producer(Resource res)
{
this.res=res;
}
public void run()
{
while(true)
{
res.set("+商品+");

}

}
}

class Consumer implements Runnable
{
private Resource res;
Consumer(Resource res)
{
this.res=res;
}
public void run()
{
while(true)
{
res.out();

}

}

}

运行结果：
Thread-0..生产者..+商品+--5857

Thread-1..消费者..+商品+--5857

Thread-0..生产者..+商品+--5858

Thread-1..消费者..+商品+--5858

Thread-0..生产者..+商品+--5859

Thread-1..消费者..+商品+--5859

Thread-0..生产者..+商品+--5860

Thread-1..消费者..+商品+--5860

Thread-0..生产者..+商品+--5861

Thread-1..消费者..+商品+--5861

Thread-0..生产者..+商品+--5862

Thread-1..消费者..+商品+--5862

Thread-0..生产者..+商品+--5863

Thread-1..消费者..+商品+--5863

Thread-0..生产者..+商品+--5864

Thread-1..消费者..+商品+--5864

Thread-0..生产者..+商品+--5865

Thread-1..消费者..+商品+--5865

Thread-0..生产者..+商品+--5866

Thread-1..消费者..+商品+--5866

Thread-0..生产者..+商品+--5867

Thread-1..消费者..+商品+--5867

同时开启两个生产着和两个消费者时：

class ConsumeDemo1
{
public static void main(String[] args)
{
Resource r = new Resource();
Producer pro = new Producer(r);
Consumer con = new Consumer(r);

Thread t1 = new Thread(pro);
Thread t2 = new Thread(pro);
Thread t3 = new Thread(con);
Thread t4 = new Thread(con);

t1.start();
t2.start();
t3.start();
t4.start();
}
}

class Resource
{
private String name;
private int count = 1;
private boolean flag = false;
public synchronized void set (String name)
{
while(flag)
try{wait();}catch(Exception e){}
this.name = name+"--"+count++;
System.out.println(Thread.currentThread().getName()+"..生产者.."+this.name);
flag = true;
this.notifyAll();
}
public synchronized void out()
{
while(!flag)
try{wait();}catch(Exception e){}
System.out.println(Thread.currentThread().getName()+"..消费者.."+this.name);
flag = false;
this.notifyAll();

}
}
class Producer implements Runnable
{
private Resource res;
Producer(Resource res)
{
this.res=res;
}
public void run()
{
while(true)
{
res.set("+商品+");

}

}
}

class Consumer implements Runnable
{
private Resource res;
Consumer(Resource res)
{
this.res=res;
}
public void run()
{
while(true)
{
res.out();

}

}

}

运行结果：

Thread-1..生产者..+商品+--6175

Thread-3..消费者..+商品+--6175

Thread-0..生产者..+商品+--6176

Thread-2..消费者..+商品+--6176

Thread-1..生产者..+商品+--6177

Thread-3..消费者..+商品+--6177

Thread-0..生产者..+商品+--6178

Thread-2..消费者..+商品+--6178

Thread-1..生产者..+商品+--6179

Thread-3..消费者..+商品+--6179

Thread-0..生产者..+商品+--6180

Thread-2..消费者..+商品+--6180

Thread-1..生产者..+商品+--6181

Thread-3..消费者..+商品+--6181

Thread-0..生产者..+商品+--6182

Thread-2..消费者..+商品+--6182

Thread-1..生产者..+商品+--6183

Thread-3..消费者..+商品+--6183

Thread-0..生产者..+商品+--6184

Thread-2..消费者..+商品+--6184

Thread-1..生产者..+商品+--6185

Thread-3..消费者..+商品+--6185

Thread-0..生产者..+商品+--6186