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 }

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 }

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 }

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 }