线程池用法的改进

引用： http://blog.csdn.net/jhycjhyc/article/details/7243728

在MSDN关于使用线程池的一个例子(见http://msdn.microsoft.com/en-us/library/3dasc8as(VS.80).aspx).程序如下:

 

 1 public class Fibonacci

 2 {

 3     public int N { get { return _n; } }

 4     private int _n;

 5 

 6     public int FibOfN { get { return _fibOfN; } }

 7     private int _fibOfN;

 8 

 9     private ManualResetEvent _doneEvent;

10 

11     public Fibonacci(int n, ManualResetEvent doneEvent)

12     {

13         _n = n;

14         _doneEvent = doneEvent;

15     }

16 

17     // Wrapper method for use with thread pool.

18     public void ThreadPoolCallback(Object threadContext)

19     {

20                 

21         int threadIndex = (int)threadContext;

22         Console.WriteLine("thread {0} started...", threadIndex);

23         _fibOfN = Calculate(_n);

24         Console.WriteLine("thread {0} result calculated...", threadIndex);

25         _doneEvent.Set();

26     }

27 

28     // Recursive method that calculates the Nth Fibonacci number.

29     public int Calculate(int n)

30     {

31         //Thread thread = Thread.CurrentThread;

32         //Console.WriteLine("[{0}] Calculate:{1}...", thread.ManagedThreadId, n);

33         if (n <= 1)

34         {

35             return n;

36         }

37         return Calculate(n - 1) + Calculate(n - 2);

38     }

39 

40 }

View Code

 

调用方法：

 1 static void Main(string[] args)

 2 {

 3     const int FibonacciCalculations = 2;  //最大只能64，超出会报错

 4 

 5     // One event is used for each Fibonacci object

 6     ManualResetEvent[] doneEvents = new ManualResetEvent[FibonacciCalculations];

 7     Fibonacci[] fibArray = new Fibonacci[FibonacciCalculations];

 8     Random r = new Random();

 9 

10     // Configure and launch threads using ThreadPool:

11     Console.WriteLine("launching {0} tasks...", FibonacciCalculations);

12     for (int i = 0; i < FibonacciCalculations; i++)

13     {

14         doneEvents[i] = new ManualResetEvent(false);

15         Fibonacci f = new Fibonacci(r.Next(20, 40), doneEvents[i]);

16         fibArray[i] = f;

17         ThreadPool.QueueUserWorkItem(new WaitCallback(f.ThreadPoolCallback), i);

18     }

19 

20     // Wait for all threads in pool to calculation...

21     WaitHandle.WaitAll(doneEvents);

22     Console.WriteLine("All calculations are complete.");

23 

24     // Display the results...

25     for (int i = 0; i < FibonacciCalculations; i++)

26     {

27         Fibonacci f = fibArray[i];

28         Console.WriteLine("Fibonacci({0}) = {1}", f.N, f.FibOfN);

29     }

30     Console.ReadLine();

31 }

View Code

以上例子是利用多线程的线程池技术进行批处理的经典范例,在实际应用中稍加改动就可以实现自己所需的功能,但遗憾的是,如果批处理的任务数大于64个时,程序运行就会出错,提示"WaitHandles 的数目必须少于或等于 64 个."以上例而言,将"const int FibonacciCalculations = 10;"改为"const int FibonacciCalculations = 65;"后再运行就会出错,这确实是一个不足,因为在实际工作中很多情况下需要用线程池技术批量处理64个以上的任务,怎么办呢?经过分析,对以上程序做了一些改动,解决了这个问题,而且程序的结构更简单,也不再需要使用 ManualResetEvent 对象,修改后的程序如下: 

 

 1 public class Fibonacci_02

 2 {

 3     public int ifdone = 0;   //注意这里

 4 

 5     public int N { get { return _n; } }

 6     private int _n;

 7 

 8     public int FibOfN { get { return _fibOfN; } }

 9     private int _fibOfN;

10 

11     public Fibonacci_02(int n)

12     {

13         _n = n;

14     }

15 

16     // Wrapper method for use with thread pool.

17     public void ThreadPoolCallback(Object threadContext)

18     {

19         int threadIndex = (int)threadContext;

20         Console.WriteLine("thread {0} started...", threadIndex);

21         _fibOfN = Calculate(_n);

22         Console.WriteLine("thread {0} result calculated...", threadIndex);

23 

24         ifdone = 1;

25     }

26 

27     // Recursive method that calculates the Nth Fibonacci number.

28     public int Calculate(int n)

29     {

30         //Thread thread = Thread.CurrentThread;

31         //Console.WriteLine("[{0}] Calculate:{1}...", thread.ManagedThreadId, n);

32         if (n <= 1)

33         {

34             return n;

35         }

36         Thread.Sleep(1);

37         return Calculate(n - 1) + Calculate(n - 2);

38     }

39 }

View Code

 

调用方法：

 1 static void Main(string[] args)

 2 {

 3     const int FibonacciCalculations = 2;//可以无限大

 4 

 5     // One event is used for each Fibonacci object

 6     Fibonacci_02[] fibArray = new Fibonacci_02[FibonacciCalculations];

 7     Random r = new Random();

 8 

 9     // Configure and launch threads using ThreadPool:

10     Console.WriteLine("launching {0} tasks...", FibonacciCalculations);

11     for (int i = 0; i < FibonacciCalculations; i++)

12     {

13         Fibonacci_02 f = new Fibonacci_02(r.Next(20, 40));

14         fibArray[i] = f;

15         ThreadPool.QueueUserWorkItem(new WaitCallback(f.ThreadPoolCallback), i);

16     }

17 

18     // Wait for all threads in pool to calculation...

19     //注意这里

20     while (true)

21     {

22         int counts = 0;

23         for (int i = 0; i < FibonacciCalculations; i++) counts = counts + fibArray[i].ifdone;

24         if (counts == FibonacciCalculations) break;

25     }

26     Console.WriteLine("All calculations are complete.");

27 

28     // Display the results...

29     for (int i = 0; i < FibonacciCalculations; i++)

30     {

31         Fibonacci_02 f = fibArray[i];

32         Console.WriteLine("Fibonacci({0}) = {1}", f.N, f.FibOfN);

33     }

34     Console.ReadLine();

35 }

View Code