// 读者写者问题
using System;
using System.Threading;
public class Book{
private int[] pages;
private bool aWriterWait = false;
private int readerCount = 0;
private object mutex = new Object(); // 控制对 readerCount 的访问
private object db = new Object(); // 控制对 pages 的访问
private object obj = new Object(); // 控制对 aWriterWait 的访问
public Book(int numOfPages){
pages = new int[numOfPages];
}
public int NumOfPages{
get{
return pages.Length; //常量，无须同步
}
}
public int this[int index]{
get{
lock(obj){
while( aWriterWait ){
Monitor.Wait(obj);
}
}
lock(mutex){
// readerCount的锁
// 检查是否为第一个读者
readerCount++;
if(readerCount == 1) Monitor.Enter(db);
}
int valueCopy = pages[index]; // 读取一个数据
Console.WriteLine( Thread.CurrentThread.Name + " 读了 第" + (index + 1) + "页，他读到的数据是" + valueCopy );
DisplayContent();
lock(mutex){
readerCount--;
if(readerCount == 0) Monitor.Exit(db);
}
return valueCopy;
}
set{
lock (obj){
aWriterWait = true;
}
lock(db){ // 阻止其他的写者去写书
pages[index] = value;
Console.WriteLine( Thread.CurrentThread.Name + "把" + value + "写到第" + (index + 1) + "页");
DisplayContent();
}
lock(obj){
aWriterWait = false;
Monitor.PulseAll(obj); // 通知等待的读者
}
}
}
private void DisplayContent(){
Console.WriteLine("{0,-35}","书的内容是:");
for(int i = 0;i < pages.Length;i++){
Console.Write("{0,-9}",pages[i]);
}
Console.WriteLine("\r\n");
}
}
public class Reader{
private Book book;
private Random rand;
public Reader(Book b,Random random){
book = b;
rand = random;
}
public void Read(){
for (int i=0; i < 5; i++){
int p = rand.Next(0,book.NumOfPages);
int a = book[p];
Thread.Sleep(rand.Next(0,100));
}
}
}
public class Writer{
private Book book;
private Random rand;
public Writer(Book b,Random random){
book = b;
rand = random;
}
public void Write(){
for(int i = 0;i < 5;i++){
int p = rand.Next(0,book.NumOfPages);
book[p] = rand.Next(50,100);
Thread.Sleep(rand.Next(0,100));
}
}
}
public class Test{
public static void Main(string[] args){
Book book = new Book(5);
Random random = new Random();
string[] readerNames = {"猪八戒","唐僧","沙和尚"};
string[] writerNames = {"观音菩萨","孙悟空","玉皇大帝"};
Thread[] readerThreads = new Thread[3];
Thread[] writerThreads = new Thread[3];
for(int i = 0;i < 3;i++){
Reader reader = new Reader(book,random);
readerThreads[i] = new Thread(new ThreadStart(reader.Read));
readerThreads[i].Name = readerNames[i];
Writer writer = new Writer(book,random);
writerThreads[i] = new Thread(new ThreadStart(writer.Write));
writerThreads[i].Name = writerNames[i];
}
for (int i=0; i<3; i++){
readerThreads[i].Start();
writerThreads[i].Start();
}
}
} 
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