Parallel.Foreach +收益回报？ [英] Parallel.Foreach + yield return?

问题描述

我想用并行循环这样的处理的内容：

I want to process something using parallel loop like this :

public void FillLogs(IEnumerable<IComputer> computers)
{
    Parallel.ForEach(computers, cpt=>
    {
        cpt.Logs = cpt.GetRawLogs().ToList();
    });

}

好吧，它工作正常。但如何做，如果我想FillLogs方法返回一个IEnumerable

Ok, it works fine. But How to do if I want the FillLogs method return an IEnumerable ?

public IEnumerable<IComputer> FillLogs(IEnumerable<IComputer> computers)
{
    Parallel.ForEach(computers, cpt=>
    {
        cpt.Logs = cpt.GetRawLogs().ToList();
        yield return cpt // KO, don't work
    });

}

修改

这似乎不是可能的...但我用这样的：

It seems not to be possible... but I use something like this :

public IEnumerable<IComputer> FillLogs(IEnumerable<IComputer> computers)
{
    return computers.AsParallel().Select(cpt => cpt);
}

在这里我把 cpt.Logs = CPT



不过， .GetRawLogs（）了ToList（）; 指令

推荐答案

短版 - 不，这不是个通过迭代器阻断T可能;较长的版本可能涉及同步队列/调用者的迭代器线程之间和平行工人（做排队）出队（做出队）;但作为一个侧面说明 - 日志通常IO绑定，并parallelising东西都是IO的限制往往不能很好地工作。

Short version - no, that isn't possible via an iterator block; the longer version probably involves synchronized queue/dequeue between the caller's iterator thread (doing the dequeue) and the parallel workers (doing the enqueue); but as a side note - logs are usually IO-bound, and parallelising things that are IO-bound often doesn't work very well.

如果主叫方是要。需要一些时间来的消耗的每一个，那么可能会有一些好处，以一种方法，一次只能处理一个记录，但能做到这一点的，而来电消耗以前登录;也就是说，它的开始 工作 作为下一个项目在收益，并为产量完成后等待 ...但是，这是一次，相当复杂。作为一个简单的例子：

If the caller is going to take some time to consume each, then there may be some merit to an approach that only processes one log at a time, but can do that while the caller is consuming the previous log; i.e. it begins a Task for the next item before the yield, and waits for completion after the yield... but that is again, pretty complex. As a simplified example:

static void Main()
{
    foreach(string s in Get())
    {
        Console.WriteLine(s);
    }
}

static IEnumerable<string> Get() {
    var source = new[] {1, 2, 3, 4, 5};
    Task<string> outstandingItem = null;
    Func<object, string> transform = x => ProcessItem((int) x);
    foreach(var item in source)
    {
        var tmp = outstandingItem;

        // note: passed in as "state", not captured, so not a foreach/capture bug
        outstandingItem = new Task<string>(transform, item);
        outstandingItem.Start();

        if (tmp != null) yield return tmp.Result;
    }
    if (outstandingItem != null) yield return outstandingItem.Result;
}
static string ProcessItem(int i)
{
    return i.ToString();
}

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