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:

 

public class Fibonacci
{
    public int N { get { return _n; } }
    private int _n;

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

    private ManualResetEvent _doneEvent;

    public Fibonacci(int n, ManualResetEvent doneEvent)
    {
        _n = n;
        _doneEvent = doneEvent;
    }

    // Wrapper method for use with thread pool.
    public void ThreadPoolCallback(Object threadContext)
    {
                
        int threadIndex = (int)threadContext;
        Console.WriteLine("thread {0} started...", threadIndex);
        _fibOfN = Calculate(_n);
        Console.WriteLine("thread {0} result calculated...", threadIndex);
        _doneEvent.Set();
    }

    // Recursive method that calculates the Nth Fibonacci number.
    public int Calculate(int n)
    {
        //Thread thread = Thread.CurrentThread;
        //Console.WriteLine("[{0}] Calculate:{1}...", thread.ManagedThreadId, n);
        if (n <= 1)
        {
            return n;
        }
        return Calculate(n - 1) + Calculate(n - 2);
    }

}

 

调用方法：

static void Main(string[] args)
{
    const int FibonacciCalculations = 2;  //最大只能64，超出会报错

    // One event is used for each Fibonacci object
    ManualResetEvent[] doneEvents = new ManualResetEvent[FibonacciCalculations];
    Fibonacci[] fibArray = new Fibonacci[FibonacciCalculations];
    Random r = new Random();

    // Configure and launch threads using ThreadPool:
    Console.WriteLine("launching {0} tasks...", FibonacciCalculations);
    for (int i = 0; i < FibonacciCalculations; i++)
    {
        doneEvents[i] = new ManualResetEvent(false);
        Fibonacci f = new Fibonacci(r.Next(20, 40), doneEvents[i]);
        fibArray[i] = f;
        ThreadPool.QueueUserWorkItem(new WaitCallback(f.ThreadPoolCallback), i);
    }

    // Wait for all threads in pool to calculation...
    WaitHandle.WaitAll(doneEvents);
    Console.WriteLine("All calculations are complete.");

    // Display the results...
    for (int i = 0; i < FibonacciCalculations; i++)
    {
        Fibonacci f = fibArray[i];
        Console.WriteLine("Fibonacci({0}) = {1}", f.N, f.FibOfN);
    }
    Console.ReadLine();
}

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: 

 

public class Fibonacci_02
{
    public int ifdone = 0;   //注意这里

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

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

    public Fibonacci_02(int n)
    {
        _n = n;
    }

    // Wrapper method for use with thread pool.
    public void ThreadPoolCallback(Object threadContext)
    {
        int threadIndex = (int)threadContext;
        Console.WriteLine("thread {0} started...", threadIndex);
        _fibOfN = Calculate(_n);
        Console.WriteLine("thread {0} result calculated...", threadIndex);

        ifdone = 1;
    }

    // Recursive method that calculates the Nth Fibonacci number.
    public int Calculate(int n)
    {
        //Thread thread = Thread.CurrentThread;
        //Console.WriteLine("[{0}] Calculate:{1}...", thread.ManagedThreadId, n);
        if (n <= 1)
        {
            return n;
        }
        Thread.Sleep(1);
        return Calculate(n - 1) + Calculate(n - 2);
    }
}

 

调用方法：

static void Main(string[] args)
{
    const int FibonacciCalculations = 2;//可以无限大

    // One event is used for each Fibonacci object
    Fibonacci_02[] fibArray = new Fibonacci_02[FibonacciCalculations];
    Random r = new Random();

    // Configure and launch threads using ThreadPool:
    Console.WriteLine("launching {0} tasks...", FibonacciCalculations);
    for (int i = 0; i < FibonacciCalculations; i++)
    {
        Fibonacci_02 f = new Fibonacci_02(r.Next(20, 40));
        fibArray[i] = f;
        ThreadPool.QueueUserWorkItem(new WaitCallback(f.ThreadPoolCallback), i);
    }

    // Wait for all threads in pool to calculation...
    //注意这里
    while (true)
    {
        int counts = 0;
        for (int i = 0; i < FibonacciCalculations; i++) counts = counts + fibArray[i].ifdone;
        if (counts == FibonacciCalculations) break;
    }
    Console.WriteLine("All calculations are complete.");

    // Display the results...
    for (int i = 0; i < FibonacciCalculations; i++)
    {
        Fibonacci_02 f = fibArray[i];
        Console.WriteLine("Fibonacci({0}) = {1}", f.N, f.FibOfN);
    }
    Console.ReadLine();
}