Mono/MonoTouch 下的 Task.Factory.StartNew() 延迟

本文介绍了Mono/MonoTouch 下的 Task.Factory.StartNew() 延迟的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

在 Mono 和 MonoTouch 下，我看到调用之间有大约 500 毫秒的延迟:

Under Mono and MonoTouch, I am seeing an approx 500 millisecond delay between when I call:

StartNew(Action<object> action, object state, CancellationToken cancellationToken, 
    TaskCreationOptions creationOptions, TaskScheduler scheduler);

以及工作代码实际开始执行的时间.

and when the worker code actually starts executing.

我创建了一个测试来显示这一点:

I created a test to show this:

public static class TestTaskFactory
{
    private class TaskInfo
    {
        public int Number;
    }

    private static int NUM_TASKS = 5;
    private static int NumFinished = 0;

    public static void Run()
    {
        for (int n = 1; n <= NUM_TASKS; n++)
        {
            Log("Starting task #" + n + " ...");
            var task_info = new TaskInfo { Number = n };
            var task = Task.Factory.StartNew(Worker, task_info, CancellationToken.None, TaskCreationOptions.None, TaskScheduler.Default);
            Thread.Sleep(0);
        }

        Log("Waiting for tasks to finish ...");
        while (NumFinished < NUM_TASKS)
        {
            Thread.Sleep(1);
        }

        Log("All done");
    }

    private static void Worker(object state)
    {
        var task_info = (TaskInfo)state;
        Log("Task #" + task_info.Number + " running");

        // Do something
        Thread.Sleep(2000);

        // Done
        ++NumFinished;
    }

    private static void Log(string msg)
    {
        Console.WriteLine(DateTime.Now.ToString("HH.mm.ss.fff") + ": Thread " + Thread.CurrentThread.ManagedThreadId + ": " + msg);
    }
}

Mac 上 Mono 下的输出:

Output under Mono on Mac:

16.57.31.420: Thread 1: Starting task #1 ...
16.57.31.508: Thread 1: Starting task #2 ...
16.57.31.508: Thread 1: Starting task #3 ...
16.57.31.508: Thread 1: Starting task #4 ...
16.57.31.508: Thread 1: Starting task #5 ...
16.57.31.508: Thread 1: Waiting for tasks to finish ...
16.57.31.510: Thread 5: Task #1 running
16.57.32.009: Thread 6: Task #2 running <-- Approx 500 msec later
16.57.32.511: Thread 7: Task #3 running <-- Approx 500 msec later
16.57.33.012: Thread 8: Task #4 running <-- Approx 500 msec later
16.57.33.513: Thread 9: Task #5 running <-- Approx 500 msec later
16.57.35.515: Thread 1: All done

就好像 Mono 想要等待最多 500 毫秒以重用现有线程，然后再生成一个新线程.如果我将工作时间减少到 500 毫秒以下，则延迟会减少.比如把worker Thread.Sleep(2000) 改成 Thread.Sleep(50):

It is as if Mono wants to wait up to 500 msec to reuse an existing thread before spawing a new one. If I decrease the worker time below 500 msec, the delay decreases. For example, changing the worker Thread.Sleep(2000) to Thread.Sleep(50):

...
17.13.20.262: Thread 5: Task #1 running
17.13.20.314: Thread 5: Task #2 running <-- approx 50 msec later
17.13.20.365: Thread 5: Task #3 running <-- approx 50 msec later
17.13.20.416: Thread 5: Task #4 running <-- approx 50 msec later
17.13.20.466: Thread 5: Task #5 running <-- approx 50 msec later

但在 MS Framework 4.0 下，工作代码启动前没有大延迟:

But under MS Framework 4.0, no large delay before worker code starts:

...
17.05.42.238: Thread 9: Waiting for tasks to finish ...
17.05.42.256: Thread 11: Task #1 running
17.05.42.256: Thread 12: Task #3 running <-- little delay
17.05.42.256: Thread 13: Task #4 running <-- little delay
17.05.42.257: Thread 10: Task #2 running <-- little delay
17.05.43.264: Thread 14: Task #5 running <-- little delay

在我提交有关 Mono 的错误报告之前，我想彻底检查一下我没有遗漏一些我需要在 Mono 上进行的调整或错误地使用 Task.Factory.我实际上在我的真实应用程序中使用了最大并发调度程序.

Before I submit a bug report on Mono, I wanted to sanity check that I am not missing some tweak I need to make on Mono or using Task.Factory wrong. I am actually using a max concurrency scheduler in my real app.

所以我的问题是:这是 Mono/MonoTouch 中的错误吗?

So my question: is this a bug in Mono/MonoTouch?

更新:我已经从使用 Mono* 下的 ThreadPool 切换到 Ami Bar 的智能线程池 (github; 代码项目文章).GSerjo 的扩展线程池看起来也不错，但是我有很多依赖项试图避免在移动设备上.我在 Xamarim 线程上写了一些简单的测试.我可能错过了 100 个其他线程池实现，但到目前为止我对 SmartThreadPool 很满意.MonoTouch下使用WINDOWS_PHONE模式编译.

Update: I've switched from using ThreadPool under Mono* to Ami Bar's Smart Thread Pool (github; Code Project article). GSerjo's Extended Thread Pool also looked nice, but had alot of dependencies that I was trying to avoid on mobile. I wrote up some of my simple testing at a Xamarim thread. I probably missed 100 other thread pool implementations, but I've been happy with SmartThreadPool so far. Use WINDOWS_PHONE mode to compile under MonoTouch.

Mono/MonoTouch 下的 Task.Factory.StartNew() 延迟

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