java 读写者问题 实现

所谓的”读者—写者问题”是指保证一个Writer进程必须与其他进程互斥地访问共享对象地同步问题.其读写操作限制(包括读者优先和写者优先):

   1)写--写互斥,即不能有两个写者同时进行写操作;

   2)读--写互斥,即不能同时有一个进程在读而另一个进程在写;

   3)读--读允许,即允许同时有多个进程在读同一个对象或文件.

 

package myprojects.rwproblem;import java.awt.*;import java.io.*;import java.lang.*;import java.util.*;public class Rwproblem{         static final int MAX_THREAD_NUM=64;         public static void main(String args[])         {             char test='0';             do             {                             System.out.println();                 System.out.println("----------Demo of Reader and Writer Problem----------");                 System.out.println("     1:Reader Priority.");                 System.out.println("     2:Writer Priority.");                 System.out.println("     3:Exit to Windows.");                 try                 {                    test=(char)System.in.read();                    System.in.read();                    }catch(IOException e){}              }while(test!='3'&&test!='1'&&test!='2');                        if(test=='3')return;                              Reader_Writer_Thread [] m_thread;                              m_thread=new Reader_Writer_Thread[MAX_THREAD_NUM];                              m_thread[0]=new Reader_Writer_Thread('r',1,3,5);                              m_thread[1]=new Reader_Writer_Thread('w',2,4,5);                              m_thread[2]=new Reader_Writer_Thread('r',3,5,2);                              m_thread[3]=new Reader_Writer_Thread('r',4,6,5);                              m_thread[4]=new Reader_Writer_Thread('w',5,5.1,3);                              if(test=='2')                              {                                       m_thread[0].setpriority(2);                                       System.out.println("   Demo of R_W Problem in Writer_Priority:");                              }                              else System.out.println("   Demo of R_W Problem in Reader_Priority:");                              m_thread[0].start();                     m_thread[1].start();                     m_thread[2].start();                     m_thread[3].start();                     m_thread[4].start();          }}class CriticalOfReader//读者临界区{         private int m_critical;         CriticalOfReader()         {                   m_critical=0;         }         public synchronized void enterCriticalSection()//进入临界区         {                   try                   {                    if(m_critical!=0)wait();                    }catch (InterruptedException e) { }             m_critical=1;         }         public synchronized void leaveCriticalSection()//离开临界区         {                   m_critical=0;                   notify();         }}class CriticalOfWriter//写者临界区{         private  int m_critical;         CriticalOfWriter()         {                   m_critical=0;         }         public synchronized void enterCriticalSection()//进入临界区         {                   try                   {                      if(m_critical!=0)wait();                    }catch (InterruptedException e) { }             m_critical=1;         }         public synchronized void leaveCriticalSection()//离开临界区         {                   m_critical=0;                   notify();         }}class Reader_Writer_Thread extends Thread{         static final int PER_SEC_DELAY=1000;//每秒运行数         private static int m_ipriority;//优先级别(1代表读者优先,2代表写者优先)         private static CriticalOfWriter m_criticalOfWriter;//写者临界区         private static CriticalOfReader m_criticalOfReader;//读者临界区         private static int m_iNumOfWriter;//写者总数         private static int m_iNumOfReader;//读者总数         private char m_chEntity;//线程类别         private int m_iSerial;//序列号         private double m_dDelay;//延迟时间         private double m_dPersist;//读持续时间         static         {                   m_ipriority=0;                   m_iNumOfWriter=0;                   m_iNumOfReader=0;                   m_criticalOfWriter=new CriticalOfWriter();                   m_criticalOfReader=new CriticalOfReader();         }         Reader_Writer_Thread(char entity,int serial,double delay,double persist)//构造函数         {                   m_chEntity=entity;                   m_iSerial=serial;                   m_dDelay=delay;                   m_dPersist=persist;         }         public boolean setpriority(int priority)//设置优先数         {                   if(priority==1||priority==2){m_ipriority=priority;return true;}                   return false;         }         public void run()//主运行         {                   //区别写者与读者线程                   if(m_chEntity=='r')reader_run();                   else if(m_chEntity=='w')writer_run();         }         public void reader_run()//读者线程运行函数         {                   try                   {                            Thread.sleep((long)m_dDelay*PER_SEC_DELAY);                   }catch(InterruptedException e){}                   Date temp=new Date();                   System.out.print(Integer.toString(temp.getMinutes())+":"                                         +Integer.toString(temp.getSeconds())+" ");                   System.out.println("Reader thread "+m_iSerial+" sends the reading require.");                   incNumOfReader();                   try                   {                            sleep((long)m_dPersist*PER_SEC_DELAY);                   }catch(InterruptedException e){}                   decNumOfReader();         }         public void writer_run()//写者线程线程运行函数         {                   try                   {                            Thread.sleep((long)m_dDelay*PER_SEC_DELAY);                   }catch(InterruptedException e){}                   Date temp=new Date();                   System.out.print(Integer.toString(temp.getMinutes())+":"                                         +Integer.toString(temp.getSeconds())+" ");                   System.out.println("Writer thread "+m_iSerial+" sends the writing require.");                   incNumOfWriter();                   try                   {                            sleep((long)m_dPersist*PER_SEC_DELAY);                   }catch(InterruptedException e){}                   decNumOfWriter();         }         public synchronized void incNumOfReader()//互斥         {                                     //写者优先时,先进入读者临界区                   if(m_ipriority==2)m_criticalOfReader.enterCriticalSection();                   //如果是第一个读者,则等待写者写完                   m_iNumOfReader++;                   if(m_iNumOfReader==1)m_criticalOfWriter.enterCriticalSection();                                     if(m_ipriority==2)m_criticalOfReader.leaveCriticalSection();//让其他读者进                   Date temp=new Date();                   System.out.print(Integer.toString(temp.getMinutes())+":"                                         +Integer.toString(temp.getSeconds())+" ");                   System.out.println("Reader thread "+m_iSerial+" begins to read the file!");         }         public synchronized void decNumOfReader()//互斥         {                   m_iNumOfReader--;                   Date temp=new Date();                   System.out.print(Integer.toString(temp.getMinutes())+":"                                         +Integer.toString(temp.getSeconds())+" ");                   System.out.println("Reader thread "+m_iSerial+" finished reading the file!");                   if(m_iNumOfReader==0)m_criticalOfWriter.leaveCriticalSection();//唤醒写者         }         public synchronized void incNumOfWriter()//互斥         {                   m_iNumOfWriter++;                   //若是写者优先,第一个写者需等待读者写完                   if(m_ipriority==2&&m_iNumOfWriter==1)m_criticalOfReader.enterCriticalSection();                   m_criticalOfWriter.enterCriticalSection();//进入写者临界区                   Date temp=new Date();                   System.out.print(Integer.toString(temp.getMinutes())+":"                                         +Integer.toString(temp.getSeconds())+" ");                   System.out.println("Writer thread "+m_iSerial+" begins to write to the file!");         }         public synchronized void decNumOfWriter()//互斥         {                   m_iNumOfWriter--;                   Date temp=new Date();                   System.out.print(Integer.toString(temp.getMinutes())+":"                                         +Integer.toString(temp.getSeconds())+" ");                   System.out.println("Reader thread "+m_iSerial+" finished writing to the file!");                   m_criticalOfWriter.leaveCriticalSection();//唤醒等待者(读者写者都有可能)                   if(m_iNumOfWriter==0&&m_ipriority==2)m_criticalOfReader.leaveCriticalSection();                   //最后一个写者,唤醒读者         }}