实验要求
5.2 构建线程A1、A2… Ak（k>=3）和线程B的程序（k生产者和单消费者）。A1、A2… Ak从磁盘各自读取一个文本文件，写入到内存中的固定的容器（如Pool）。A1、A2… Ak读取每一行时，都会休眠，然后在随机的时间（10–100 ms）醒来继续尝试执行。程序要求按照A1、A2… Ak的顺序写入Pool。B会观察Pool的状态，如果有新数据，则进行读取，否则B处于等待状态。注意，A1、A2… Ak不能互相干扰。当所有的文件被读取完毕，且B读取完毕时，程序结束。
不推荐阅读
以下部分内容表述较不准确；由于我个人对多线程掌握得并不是很优秀，代码也不一定完全正确。但作为应付作业已经足够，谨慎阅读 。
实验环境
Visual Studio 2019 + C#开发环境
算法设计
由于k个读取文件的线程内容基本相同，我们便只介绍一个，其他都相同，不再赘述：
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| public void ReadA1(object stateInfo)
{
Monitor.Enter(this);
if (flag != 1) Monitor.Wait(this);
Console.WriteLine("enter 1");
FileStream file = File.OpenRead("text_a1.txt");
StreamReader stream = new StreamReader(file, System.Text.Encoding.Default);
file.Seek(0, SeekOrigin.Begin);
while (stream.Peek() > -1)
{
strFromTxt = stream.ReadLine();
Thread.Sleep(r.Next(10, 100));
writeFlag = 1;
}
Console.WriteLine("quit 1");
flag = 2;
Monitor.Pulse(this);
Monitor.Exit(this);
}
|
首先介绍一下 Monitor.Wait() 与 Monitor.Pulse() 函数：前者用来将当前线程置于等待序列，直到其被移出等待序列后开始执行；而后者则是将当前锁的其他线程移出队列开始执行，发出一段脉冲信号。我们可以用这两个函数加上一个 flag 标记实现线程的异步，达到顺序执行的效果。
由于实验要求中需要我们每读一行字符就写入B中一次，所以我们需要一个标记 writeFlag 来判断是否需要写入。
再来看写入文件的线程B：
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| public void WriteB(object stateInfo)
{
FileStream file = File.OpenWrite("text_b.txt");
StreamWriter stream = new StreamWriter(file, System.Text.Encoding.Default);
while (true)
{
if (writeFlag ==1)
{
stream.WriteLine(strFromTxt);
writeFlag = 0;
}
if (flag == 0) break;
}
stream.Close();
}
|
由于线程B需要随时运行以进行实时读入文件，其并不需要加锁，可以自由运行。但循环中需要通过 writeFlag 标记来判断是否需要写入。最终当三个线程都读取完后，flag 标记变为0，即退出循环，并关闭文件进行保存。
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| public void Start()
{
ThreadPool.QueueUserWorkItem(new WaitCallback(ReadA1));
ThreadPool.QueueUserWorkItem(new WaitCallback(ReadA2));
ThreadPool.QueueUserWorkItem(new WaitCallback(ReadA3));
ThreadPool.QueueUserWorkItem(new WaitCallback(WriteB));
while (flag != 0) ;
Thread.Sleep(r.Next(10, 100));
}
|
而在主函数中，我们则通过线程池直接创建线程，将四个线程都加入线程池，直到 flag = 0 ，即线程被运行完后，稍作等待所有操作完成后，退出程序。
完整代码
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| using System;
using System.IO;
using System.Threading;
namespace ThreadTest
{
class Program
{
static void Main(string[] args)
{
ReadAndWrite readAndWrite = new ReadAndWrite();
readAndWrite.Start();
}
}
class ReadAndWrite
{
int flag;
string strFromTxt;
int writeFlag;
Random r = new Random();
public ReadAndWrite()
{
flag = 1;
writeFlag = 0;
strFromTxt = "";
}
public void ReadA1(object stateInfo)
{
Monitor.Enter(this);
if (flag != 1) Monitor.Wait(this);
Console.WriteLine("enter 1");
FileStream file = File.OpenRead("text_a1.txt");
StreamReader stream = new StreamReader(file, System.Text.Encoding.Default);
file.Seek(0, SeekOrigin.Begin);
while (stream.Peek() > -1)
{
strFromTxt = stream.ReadLine();
Thread.Sleep(r.Next(10, 100));
writeFlag = 1;
}
Console.WriteLine("quit 1");
flag = 2;
Monitor.Pulse(this);
Monitor.Exit(this);
}
public void ReadA2(object stateInfo)
{
Monitor.Enter(this);
if (flag != 2) Monitor.Wait(this);
Console.WriteLine("enter 2");
FileStream file = File.OpenRead("text_a2.txt");
StreamReader stream = new StreamReader(file, System.Text.Encoding.Default);
file.Seek(0, SeekOrigin.Begin);
while (stream.Peek() > -1)
{
strFromTxt = stream.ReadLine();
Thread.Sleep(r.Next(10, 100));
writeFlag = 1;
}
Console.WriteLine("quit 2");
flag = 3;
Monitor.Pulse(this);
Monitor.Exit(this);
}
public void ReadA3(object stateInfo)
{
Monitor.Enter(this);
if (flag != 3) Monitor.Wait(this);
Console.WriteLine("enter 3");
FileStream file = File.OpenRead("text_a3.txt");
StreamReader stream = new StreamReader(file, System.Text.Encoding.Default);
file.Seek(0, SeekOrigin.Begin);
while (stream.Peek() > -1)
{
strFromTxt = stream.ReadLine();
Thread.Sleep(r.Next(10, 100));
writeFlag = 1;
}
Console.WriteLine("quit 3");
flag = 0;
Monitor.Pulse(this);
Monitor.Exit(this);
}
public void WriteB(object stateInfo)
{
FileStream file = File.OpenWrite("text_b.txt");
StreamWriter stream = new StreamWriter(file, System.Text.Encoding.Default);
while (true)
{
if (writeFlag ==1)
{
stream.WriteLine(strFromTxt);
writeFlag = 0;
}
if (flag == 0) break;
}
stream.Close();
}
public void Start()
{
ThreadPool.QueueUserWorkItem(new WaitCallback(ReadA1));
ThreadPool.QueueUserWorkItem(new WaitCallback(ReadA2));
ThreadPool.QueueUserWorkItem(new WaitCallback(ReadA3));
ThreadPool.QueueUserWorkItem(new WaitCallback(WriteB));
while (flag != 0) ;
Thread.Sleep(r.Next(10, 100));
}
}
}
|
测试数据
//text_a1:
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| a_line1
a_line2
a_line3
a_line4
a_line5
----a_end----
|
//text_a2:
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2
3
4
5
| b_line1
b_line2
b_line3
b_line4
----b_end----
|
//text_a3:
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2
3
4
| c_line1
c_line2
c_line3
----c_end----
|
//text_b(output):
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| a_line1
a_line2
a_line3
a_line4
a_line5
----a_end----
b_line1
b_line2
b_line3
b_line4
----b_end----
c_line1
c_line2
c_line3
----c_end----
|
