JAVA多线程实现读者写者问题

当有线程正在读的时候，不允许写 线程写，但是允许其他的读线程进行读。有写线程正在写的时候，其他的线程不应该读写。为了防止写线程出现饥饿现象，当线程正在读，如果写线程请求写，那么应该禁止再来的读线程进行读。

实现代码如下：

File.java

package readerWriter;public class File {private String name;public File(String name){this.name=name;}}

Pool.java

package readerWriter;public class Pool {private int readerNumber=0;private int writerNumber=0;private boolean waittingWriten;public boolean isWaittingWriten() {return waittingWriten;}public void setWaittingWriten(boolean waittingWriten) {this.waittingWriten = waittingWriten;}public File getFile() {return file;}public void setFile(File file) {this.file = file;}File file;public Pool(File file){this.file=file;}public int getReaderNumber() {return readerNumber;}public void setReaderNumber(int readerNumber) {this.readerNumber = readerNumber;}public int getWriterNumber() {return writerNumber;}public void setWriterNumber(int writerNumber) {this.writerNumber = writerNumber;}}

Reader.java

package readerWriter;public class Reader  implements Runnable{    private String id;private Pool pool;            public Reader(String id,Pool pool)    {    this.id=id;    this.pool=pool;    }        @Overridepublic void run(){// TODO Auto-generated method stubwhile(!Thread.currentThread().interrupted()){synchronized(pool){while(pool.getWriterNumber()>0 || pool.isWaittingWriten()==true)//当线程正在写或者                                                            //有线程正在等待写，则禁止读线程继续读  {try {pool.wait();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}{pool.setReaderNumber(pool.getReaderNumber()+1); }}  System.out.println(id+"  "+"is reading....");   try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}synchronized(pool){   pool.setReaderNumber(pool.getReaderNumber()-1);     System.out.println(id+"   "+"is existing the reader....");   if(pool.getReaderNumber()==0)            pool.notifyAll();    }  try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}// pool.notifyAll();    }  }}

Writer.java

package readerWriter;public class Writer implements Runnable{   private Pool pool;   String id;   public Writer(String id,Pool pool)   {   this.id=id;   this.pool=pool;         }@Overridepublic void run() {// TODO Auto-generated method stubwhile(!Thread.currentThread().interrupted()){synchronized(pool){if(pool.getReaderNumber()>0)pool.setWaittingWriten(true);elsepool.setWaittingWriten(false);//当线程正在被读或者被写或者有线程等待读while(pool.getWriterNumber()>0  ||   pool.getReaderNumber()>0)   {try {pool.wait();   } catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}pool.setWaittingWriten(false);   //这个策略还算公平{pool.setWriterNumber(pool.getWriterNumber()+1); }} System.out.println(id+"  "+"is writing....");  try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}    //synchronized(pool){   pool.setWriterNumber(pool.getWriterNumber()-1);   System.out.println(id+"   "+"is existing the  writer....");   pool.notifyAll();    } /* try {Thread.sleep(1000);//System.out.println("writer sleeping over");} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}  */    }}}

Main.java

package readerWriter;public class Main {public static void main(String[] args) {// TODO Auto-generated method stubPool pool=new Pool(new File("dd file"));for(int i=0;i<2;i++){  Thread writer=new Thread(new Writer("writer "+i,pool));  writer.start();}for(int i=0;i<5;i++){Thread reader=new Thread(new Reader("reader "+i,pool));reader.start();}}}

程序部分运行结果如下：

writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....reader 0  is reading....reader 0   is existing the reader....writer 1  is writing....writer 1   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....reader 3  is reading....reader 2  is reading....reader 4  is reading....reader 1  is reading....reader 0  is reading....reader 3   is existing the reader....reader 1   is existing the reader....reader 0   is existing the reader....reader 4   is existing the reader....reader 2   is existing the reader....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 1  is writing....writer 1   is existing the  writer....reader 2  is reading....reader 2   is existing the reader....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....writer 0   is existing the  writer....writer 0  is writing....