java实现多线程间的同步与互斥（读者写者问题）

import java.util.HashMap; import java.util.Map; import java.util.Random; /** * Created by 32706 on 2016/12/24. */ public class ReadThread extends Thread { public int id;// 读者ID //public static int readCount=0;// 读者数量 public static Map<Integer,Integer> readCountMap=new HashMap<>();//存放每一行的读者数量 public static void init_readthread_readcountmap() { for(int i=0;i<ReadAndWrite.Value.length;i++) { readCountMap.put(i,0); } } public ReadThread(int id) { this.id = id; } private double get_avrage(int i,int j,int k) { double sum=0; for(int r=j;r<=k;r++) sum=ReadAndWrite.Value[i][r]+sum; return sum/(k-j+1); } //读者优先 public void run() { try{ for(int x=0;x<ReadAndWrite.execute_times;x++) { int thread_i=(int)(Math.random()*20)%10; int thread_j=(int) (Math.random()*200000)%100000; int thread_k=(int)(Math.random()*200000)%(100000-thread_j)+thread_j; try { //没人在写 if(ReadAndWrite.writeSemaphoreMap.get(thread_i).availablePermits()>0)//可以读 { System.out.println(id+"号读线程准备读取第"+thread_i+"行的"+thread_j+"=>"+thread_k+"的数据"+" "+ System.currentTimeMillis()); } else { System.out.println("有写线程在写操作，"+id+"号线程等待读===="+" "+ System.currentTimeMillis()); } // 等待着读 ReadAndWrite.readCountSemaphoreMap.get(thread_i).acquire();//如果读者过多则会等待，读者小于5则可以读 if (readCountMap.get(thread_i) == 0)//如果是第i行的第一个读者，那么要考虑是否有写者，没有写者，直接读，有写者，等待写者 { //此时不能写 int readCount=readCountMap.get(thread_i)+1;// 已经具备读的条件了，读者数量加1 readCountMap.put(thread_i,readCount); ReadAndWrite.writeSemaphoreMap.get(thread_i).acquire();//上写锁 } ReadAndWrite.readCountSemaphoreMap.get(thread_i).release(); /**********************************/ //此刻才可以允许其他读者读数据 /**********************************/ ReadAndWrite.readCountSemaphoreMap.get(thread_i).acquire(); //可以读了 System.out.println(id+"号读线程正在读取数据...."+" "+ System.currentTimeMillis()); Thread.sleep((long) (new Random().nextFloat()*1000)); System.out.println(id+"号读线程计算结果为~~~~"+get_avrage(thread_i,thread_j,thread_k)+" "+ System.currentTimeMillis()); //读完了，读者数量减少1 int readCounttem=readCountMap.get(thread_i)-1; readCountMap.put(thread_i,readCounttem); if(readCountMap.get(thread_i)==0)//没有读者了，可以写了 { ReadAndWrite.writeSemaphoreMap.get(thread_i).release(); } ReadAndWrite.readCountSemaphoreMap.get(thread_i).release();//释放读者信号量 Thread.sleep((long) (new Random().nextFloat()*1000)); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } finally{ ReadAndWrite.Runningthread++; } } }