C#中的并行迭代?

.NET 4的BlockingCollection使这变得非常容易。创建一个BlockingCollection,返回它的值。enumerable方法中的GetConsuringEnumerable()。然后foreach简单地添加到阻塞集合中。

例如

private BlockingCollection<T> m_data = new BlockingCollection<T>();

public IEnumerable<T> GetData( IEnumerable<IEnumerable<T>> sources )
{
    Task.Factory.StartNew( () => ParallelGetData( sources ) );
    return m_data.GetConsumingEnumerable();
}

private void ParallelGetData( IEnumerable<IEnumerable<T>> sources )
{
    foreach( var source in sources )
    {
        foreach( var item in source )
        {
            m_data.Add( item );
        };
    }

    //Adding complete, the enumeration can stop now
    m_data.CompleteAdding();
}

希望这能有所帮助。 顺便说一句 posted a blog about this 昨晚

安德烈

简短的回答,没有。 foreach 一次只处理一个可枚举项。

但是,如果将并行枚举组合成一个,则可以 循环 在组合。我不知道有什么简单的内置方法可以做到这一点,但以下方法应该有效(尽管我没有测试过):

public IEnumerable<TSource[]> Combine<TSource>(params object[] sources)
{
    foreach(var o in sources)
    {
        // Choose your own exception
        if(!(o is IEnumerable<TSource>)) throw new Exception();
    }

    var enums =
        sources.Select(s => ((IEnumerable<TSource>)s).GetEnumerator())
        .ToArray();

    while(enums.All(e => e.MoveNext()))
    {
        yield return enums.Select(e => e.Current).ToArray();
    }
}

那么你可以 循环 在返回的枚举值之上:

foreach(var v in Combine(en1, en2, en3))
{
    // Remembering that v is an array of the type contained in en1,
    // en2 and en3.
}

Zooba的答案很好,但你可能也想看看以下问题的答案 "How to iterate over two arrays at once" .

我从中编写了EachParallel()的实现。NET4并行库。它与兼容。净值3.5: Parallel ForEach Loop in C# 3.5 用途:

string[] names = { "cartman", "stan", "kenny", "kyle" };
names.EachParallel(name =>
{
    try
    {
        Console.WriteLine(name);
    }
    catch { /* handle exception */ }
});

实施:

/// <summary>
/// Enumerates through each item in a list in parallel
/// </summary>
public static void EachParallel<T>(this IEnumerable<T> list, Action<T> action)
{
    // enumerate the list so it can't change during execution
    list = list.ToArray();
    var count = list.Count();

    if (count == 0)
    {
        return;
    }
    else if (count == 1)
    {
        // if there's only one element, just execute it
        action(list.First());
    }
    else
    {
        // Launch each method in it's own thread
        const int MaxHandles = 64;
        for (var offset = 0; offset < list.Count() / MaxHandles; offset++)
        {
            // break up the list into 64-item chunks because of a limitiation             // in WaitHandle
            var chunk = list.Skip(offset * MaxHandles).Take(MaxHandles);

            // Initialize the reset events to keep track of completed threads
            var resetEvents = new ManualResetEvent[chunk.Count()];

            // spawn a thread for each item in the chunk
            int i = 0;
            foreach (var item in chunk)
            {
                resetEvents[i] = new ManualResetEvent(false);
                ThreadPool.QueueUserWorkItem(new WaitCallback((object data) =>
                {
                    int methodIndex = (int)((object[])data)[0];

                    // Execute the method and pass in the enumerated item
                    action((T)((object[])data)[1]);

                    // Tell the calling thread that we're done
                    resetEvents[methodIndex].Set();
                }), new object[] { i, item });
                i++;
            }

            // Wait for all threads to execute
            WaitHandle.WaitAll(resetEvents);
        }
    }
}

如果你想坚持基本原则,我以更简单的方式重写了目前接受的答案:

    public static IEnumerable<TSource[]> Combine<TSource> (this IEnumerable<IEnumerable<TSource>> sources)
    {
        var enums = sources
            .Select (s => s.GetEnumerator ())
            .ToArray ();

        while (enums.All (e => e.MoveNext ())) {
            yield return enums.Select (e => e.Current).ToArray ();
        }
    }

    public static IEnumerable<TSource[]> Combine<TSource> (params IEnumerable<TSource>[] sources)
    {
        return sources.Combine ();
    }

这对你有用吗?

public static class Parallel
{
    public static void ForEach<T>(IEnumerable<T>[] sources,
                                  Action<T> action)
    {
        foreach (var enumerable in sources)
        {
            ThreadPool.QueueUserWorkItem(source => {
                foreach (var item in (IEnumerable<T>)source)
                    action(item);
            }, enumerable);
        }
    }
}

// sample usage:
static void Main()
{
    string[] s1 = { "1", "2", "3" };
    string[] s2 = { "4", "5", "6" };
    IEnumerable<string>[] sources = { s1, s2 };
    Parallel.ForEach(sources, s => Console.WriteLine(s));
    Thread.Sleep(0); // allow background threads to work
}

对于C#2.0,您需要将上述lambda表达式转换为委托。

注意:此实用程序方法使用后台线程。您可能希望修改它以使用前台线程,并且可能希望等待所有线程完成。如果你这样做,我建议你创建 sources.Length - 1 线程,并将当前执行线程用于最后一个(或第一个)源。

(我希望我可以在代码中包含等待线程完成,但很抱歉,我还不知道该怎么做。我想你应该使用 一 WaitHandle Thread.Join() .)