Question

我有30多个可以并行执行的任务我为每项任务使用ThreadPool 但是在完成所有任务之前，父函数不应该返回。

我需要一个线程同步句柄，当它的计数达到0时会释放WaitOne。类似的东西：

foo.StartWith(myTasks.Count);
foreach (var task in myTasks) {
    ThreadPool.QueueUserWorkItem(state => { task(state); foo.Release(); });
}
foo.WaitOne();

Semaphore感觉正确，只是无法弄清楚如何在这里应用它。

Answer 1

int running = myTasks.Count;
AutoResetEvent done = new AutoResetEvent(false);
foreach (var task in myTasks) {
    ThreadPool.QueueUserWorkItem(state => { 
    task(state); 
    if (0 == Interlocked.Decrement(ref running))
      done.Set ();
    });
}
done.WaitOne();

使用C＃4.0，您可以使用新的CountdownEvent原语。

Answer 2

Joe Duffy写了一篇关于此类事情的精彩文章：

CLR Inside Out: 9 Reusable Parallel Data Structures and Algorithms

我正在将CountdownLatch视为特别适合您的要求。

Answer 3

根据这篇文章：Overview of Synchronization Primitives

C＃具有此场景的内置类型，CountDownEvent：CountdownEvent Class

或类似的：Barrier (.NET Framework)

对于较新版本，请使用TPL（任务并行库），对于此场景，此代码是相关的：

// Create an ActionBlock<int> object that prints its input
// and throws ArgumentOutOfRangeException if the input
// is less than zero.
var throwIfNegative = new ActionBlock<int>(n =>
{
   Console.WriteLine("n = {0}", n);
   if (n < 0)
   {
      throw new ArgumentOutOfRangeException();
   }
});

// Post values to the block.
throwIfNegative.Post(0);
throwIfNegative.Post(-1);
throwIfNegative.Post(1);
throwIfNegative.Post(-2);
throwIfNegative.Complete();

// Wait for completion in a try/catch block.
try
{
   throwIfNegative.Completion.Wait();
}
catch (AggregateException ae)
{
   // If an unhandled exception occurs during dataflow processing, all
   // exceptions are propagated through an AggregateException object.
   ae.Handle(e =>
   {
      Console.WriteLine("Encountered {0}: {1}", 
         e.GetType().Name, e.Message);
      return true;
   });
}

/* Output:
n = 0
n = -1
Encountered ArgumentOutOfRangeException: Specified argument was out of the range
 of valid values.
*/

来自https://msdn.microsoft.com/en-us/library/hh228603.aspx

从线程池加入线程

3 个答案: