c# – 使用ThreadPool.QueueUserWorkItem对线程进行排序

while(queue.count>0){
  File f = queue.Dequeue(); //get File from queue       
  OperationList oprlst = getOperationsForFile(f); 
// will get list-> [a1,a5]   
  for each Operation oprn in oprlst 
  {
    performOperation(f,oprn)
    //in MTA i want to wait till operation "a1" completes and then operation "a2" will
   //start.making threads wait till file is in use or operation a(i) is in use.
  }    
}

您应该避免在ThreadPool线程中使用诸如Monitor锁和WaitHandle结构之类的线程阻塞技术,因为这些线程被其他进程使用.您需要使用基于单个文件的线程.如果单个文件没有花费那么长的时间来处理(并且你没有太多的文件),那么ThreadPool将会工作.

ThreadPool实现

您可以在以文件为中心的方法上使用EnqueueUserWorkItem ……这样的事情：

private void ProcessFile(Object data)
{ 
    File f = (File)data;

    foreach(Operation oprn in getOperationsForFile(f))
    {
        performOperation(f,oprn);
    }
}

然后在处理文件的代码中,执行以下操作：

while(queue.Count > 0)
{
    ThreadPool.QueueUserWorkItem(new WaitCallback(ProcessFile),queue.Dequeue());
}

如果你需要你的调用线程阻塞直到它们都完整,那么WaitHandle就可以了(因为你阻塞了你自己的线程,而不是ThreadPool线程).但是,您必须创建一个小的有效负载类来将其传递给线程：

private class Payload
{
    public File File;
    public AutoResetEvent Handle;
}

private void ProcessFile(Object data)
{ 
    Payload p = (Payload)data;

    foreach(Operation oprn in getOperationsForFile(p.File))
    {
        performOperation(f,oprn);
    }

    p.Handle.Set();
}

...

WaitHandle[] handles = new WaitHandle[queue.Count];
int index = 0;

while(queue.Count > 0)
{        
    handles[index] = new AutoResetEvent();

    Payload p = new Payload();

    p.File = queue.Dequeue();
    p.Handle = handles[index];

    ThreadPool.QueueUserWorkItem(new WaitCallback(ProcessFile),p);

    index++;
}

WaitHandle.WaitAll(handles);

线程实现

但是,如果您有大量文件(或者文件可能需要花费大量时间来处理),那么创建自己的线程是个更好的主意.这也可以让你省略WaitHandles.

private void ProcessFile(File f)
{     
    foreach(Operation oprn in getOperationsForFile(f))
    {
        performOperation(f,oprn);
    }

    p.Handle.Set();
}

private object queueLock = new object();

private void ThreadProc()
{
    bool okToContinue = true;

    while(okToContinue)
    {
        File f = null;

        lock(queueLock)
        {
            if(queue.Count > 0) 
            {
                f = queue.Dequeue();
            }
            else
            {
                f = null;
            }
        }

        if(f != null)
        {
            ProcessFile(f);
        }
        else
        {
            okToContinue = false;
        }
    }
}

...

Thread[] threads = new Thread[20]; // arbitrary number,choose the size that works

for(int i = 0; i < threads.Length; i++)
{
    threads[i] = new Thread(new ThreadStart(ThreadProc));

    thread[i].Start();
}

//if you need to wait for them to complete,then use the following loop:
for(int i = 0; i < threads.Length; i++)
{
    threads[i].Join();
}

前面的示例是一个非常基本的线程池,但它应该说明需要做什么.