为什么并行任务没有运行?

问题描述

我有这个代码，它是为了证明问题而剥离的更大功能的骨架:

I have this code, it is the skeleton of larger functionality stripped down to prove the problem:

        var tasks = Enumerable.Range(0, 10)
            .Select(laneNo => Task.Run(() => Console.WriteLine($"Starting generator for lane {laneNo}")));

        for(int r=0; ;++r)
        {
            Task.Delay(TimeSpan.FromSeconds(3)).Wait();

            Console.WriteLine($"Iteration {r} at {DateTime.Now}");
        }

我从来没有看到启动生成器"打印到控制台，但我确实看到迭代每 3 秒触发一次 - 有些事情导致这些任务没有进展(在实际代码中，它们运行了很长一段时间，但删除它不会影响问题).

I never see "Starting generator" printed to Console but I do see the iteration fire every 3 seconds - something is causing those tasks not to progress (in the real code they run for a significant period but removing that doesn't affect the problem).

为什么第一批任务没有运行?我的理论是它与 Task.Delay 相关?

Why are the first bunch of Tasks not running? My theory is it's related to Task.Delay?

推荐答案

LINQ Select 已延迟执行；它只是定义了一个迭代器，所以你的 Task 不会被生成.

LINQ Select has deferred execution; it simply defines an iterator, so your Tasks are not being generated.

您可以使用 Task.WhenAll(IEnumerable)，它将迭代并等待每个Task，生成新的Task代码>在所有提供的任务也完成后完成:

You could make use of Task.WhenAll(IEnumerable<Task>), which will iterate and await each Task, generating new Task that completes once all the provided tasks have also completed:

var tasks = Enumerable.Range(0, 10)
        .Select(laneNo => Task.Run(() => Console.WriteLine($"Starting generator for lane {laneNo}")));

await Task.WhenAll(tasks);

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