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java 多线程饥饿现象的问题解决方法

2020-11-12 17:39m1457285665 JAVA教程

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java 多线程饥饿现象的问题解决方法

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

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

Pool.java

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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

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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;
  }
   
   
  @Override
  public void run()
  {
    // TODO Auto-generated method stub
    while(!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 block
                e.printStackTrace();
              }
             
           
           
        }
       
      {
         
        pool.setReaderNumber(pool.getReaderNumber()+1); 
          
         
      }
    }
     System.out.println(id+" "+"is reading....");
      
     try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      // TODO Auto-generated catch block
      e.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 block
      e.printStackTrace();
    }
    // pool.notifyAll();
     
      
      
  }
      
       
   
     
     
  }
   
 
}

Writer.java

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package readerWriter;
 
public class Writer implements Runnable{
  private Pool pool;
  String id;
  public Writer(String id,Pool pool)
  {
    this.id=id;
    this.pool=pool;
     
     
  }
  @Override
  public void run() {
    // TODO Auto-generated method stub
    while(!Thread.currentThread().interrupted()){
       
    synchronized(pool){
      if(pool.getReaderNumber()>0)
        pool.setWaittingWriten(true);
      else
        pool.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 block
            e.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 block
      e.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 block
        e.printStackTrace();
      } */
     
      
      
  }
 
}
}

Main.java

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package readerWriter;
 
public class Main {
 
  public static void main(String[] args) {
    // TODO Auto-generated method stub
Pool 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:

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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....

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原文链接:http://blog.csdn.net/m1457285665/article/details/44501339

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