秒表多任务 ElapsedMilliseconds 计算答案

【问题标题】：Stopwatch multi-task ElapsedMilliseconds calculation秒表多任务 ElapsedMilliseconds 计算
【发布时间】：2018-10-26 00:37:25
【问题描述】：

我有一个非常基本的函数来跟踪每个函数调用所花费的时间。 UnitWorkAsync 中的秒表返回预期值，但 ParentWorkAsync 中的计时器不断添加跨任务的时间。秒表跟踪我做错了什么？

在输出中，我假设 ParentWorkAsync 计时器与 UnitWorkAsync 计时器大致相同，但情况并非如此，如下所示

代码

class StopwatchTestHelper
{
    private static int workItemsCount = 0;

    public void Run()
    {
        List<Task> tasks = new List<Task>();

        Stopwatch stopwatch = Stopwatch.StartNew();

        for (int i = 0; i < 1000; i++)
        {
            tasks.Add(ParentWorkAsync());
        }

        Task.WaitAll(tasks.ToArray());

        Console.WriteLine("Run timer: " + stopwatch.ElapsedMilliseconds);
    }

    private async Task ParentWorkAsync()
    {
        Stopwatch stopwatch = Stopwatch.StartNew();

        await UnitWorkAsync().ConfigureAwait(false);

        Console.WriteLine("ParentWorkAsync timer: " + stopwatch.ElapsedMilliseconds);
    }

    private async Task UnitWorkAsync()
    {
        await Task.Yield();

        Stopwatch stopwatch = Stopwatch.StartNew();

        // Blocking call.
        //
        Thread.Sleep(2000);

        // Async call.
        //
        await Task.Delay(100);

        Console.WriteLine("UnitWorkAsync timer: " + stopwatch.ElapsedMilliseconds);

        Interlocked.Increment(ref workItemsCount);
        Console.WriteLine("Work items completed: " + workItemsCount);
    }
}

输出：

UnitWorkAsync timer: 2963
Work items completed: 1
ParentWorkAsync timer: 2973
UnitWorkAsync timer: 2998
Work items completed: 2
ParentWorkAsync timer: 3966
UnitWorkAsync timer: 2954
Work items completed: 3
ParentWorkAsync timer: 4956
UnitWorkAsync timer: 2993
Work items completed: 4
ParentWorkAsync timer: 5955
UnitWorkAsync timer: 2954
Work items completed: 5
ParentWorkAsync timer: 6952
UnitWorkAsync timer: 2993
Work items completed: 6
ParentWorkAsync timer: 7951

【问题讨论】：

准确的说，代码火烧线程池。除非你花很多钱，否则你不可能有一千个线程同时执行代码。随意将 Thread.Sleep() 替换为 await Task.Delay 看看有什么不同。

标签： c# asynchronous stopwatch

【解决方案1】：

Hans Passant 在他的 cmets 中绝对正确

首先

当你启动一个任务时，并不能保证它会启动自己的线程

其次

当您调用 Thread.Sleep 时，它会以句号休眠该线程，没有 pass-go。

第三

通过正确使用await，它允许线程在需要之前返回到池中，这反过来又使任务调度程序有机会重用该线程并允许资源分配更有效

解决办法

如果您将Thread.Sleep 替换为await Task.Delay(2000)，您会发现这将按预期工作。 T

问题

这里的问题是调度程序不会一次给你所有的线程，它只会提供它认为基于一组规则、一些启发式（和秘诀）你应该拥有的东西，只是在开玩笑）。在这种Thread.Sleep 的情况下，调度程序对您正在做的事情采取了模糊的看法，并没有让您拥有您可能喜欢的所有线程。

现在让我们证明一下

修改后的代码

private static async Task ParentWorkAsync()
{
   Stopwatch sw = Stopwatch.StartNew();

   var num = _rand.Next(100000);

   Console.WriteLine($"P Start : {GetInfo(num,sw)}");

   await UnitWorkAsync(num,sw).ConfigureAwait(false);

   Console.WriteLine($"P Stop : {GetInfo(num,sw)}");
}

private  static async Task UnitWorkAsync(int num, Stopwatch sw)
{
   await Task.Yield();

   Console.WriteLine($"W Start : {GetInfo(num,sw)}");

   Thread.Sleep(2000);

   Interlocked.Decrement(ref workItemsCount);

   Console.WriteLine($"W Stop : {GetInfo(num,sw)}");    
}

这是8个任务，

W 和 P 代表父母和工人
Id = 用于跟踪事件的随机数
经过 = 使用经过时间形式的同一秒表从开始到结束
线程数 = 任意一点正在使用的线程数
ThreadId = 是线程id

8 任务开始

P Start : id 83868, Elapsed 0, Threads 0, ThreadId 1
W Start : id 83868, Elapsed 30, Threads 1, ThreadId 3
P Start : id 99383, Elapsed 0, Threads 1, ThreadId 1
P Start : id 53213, Elapsed 0, Threads 3, ThreadId 1
W Start : id 99383, Elapsed 0, Threads 4, ThreadId 4
P Start : id 54079, Elapsed 0, Threads 4, ThreadId 1
P Start : id 44978, Elapsed 0, Threads 5, ThreadId 1
W Start : id 53213, Elapsed 1, Threads 7, ThreadId 5
P Start : id 38396, Elapsed 0, Threads 7, ThreadId 1
P Start : id 30429, Elapsed 0, Threads 8, ThreadId 1
W Start : id 54079, Elapsed 1, Threads 8, ThreadId 8
W Start : id 44978, Elapsed 1, Threads 8, ThreadId 6
P Start : id 49184, Elapsed 0, Threads 8, ThreadId 1
W Start : id 38396, Elapsed 2, Threads 8, ThreadId 9
W Start : id 30429, Elapsed 2, Threads 8, ThreadId 10
W Start : id 49184, Elapsed 1, Threads 8, ThreadId 7
W Stop : id 83868, Elapsed 2031, Threads 8, ThreadId 3
P Stop : id 83868, Elapsed 2032, Threads 8, ThreadId 3
W Stop : id 99383, Elapsed 2001, Threads 8, ThreadId 4
P Stop : id 99383, Elapsed 2001, Threads 7, ThreadId 4
W Stop : id 53213, Elapsed 2002, Threads 6, ThreadId 5
P Stop : id 53213, Elapsed 2002, Threads 6, ThreadId 5
W Stop : id 54079, Elapsed 2002, Threads 5, ThreadId 8
P Stop : id 54079, Elapsed 2003, Threads 5, ThreadId 8
W Stop : id 44978, Elapsed 2002, Threads 5, ThreadId 6
P Stop : id 44978, Elapsed 2002, Threads 4, ThreadId 6
W Stop : id 38396, Elapsed 2002, Threads 3, ThreadId 9
P Stop : id 38396, Elapsed 2002, Threads 3, ThreadId 9
W Stop : id 49184, Elapsed 2002, Threads 2, ThreadId 7
P Stop : id 49184, Elapsed 2002, Threads 2, ThreadId 7
W Stop : id 30429, Elapsed 2003, Threads 2, ThreadId 10
P Stop : id 30429, Elapsed 2003, Threads 1, ThreadId 10

一切看起来都不错

10 个任务开始

P Start : id 63043, Elapsed 0, Threads 0, ThreadId 1
W Start : id 63043, Elapsed 15, Threads 1, ThreadId 3
P Start : id 28942, Elapsed 0, Threads 1, ThreadId 1
P Start : id 80940, Elapsed 0, Threads 3, ThreadId 1
W Start : id 28942, Elapsed 0, Threads 3, ThreadId 4
P Start : id 81431, Elapsed 0, Threads 4, ThreadId 1
P Start : id 89951, Elapsed 0, Threads 5, ThreadId 1
W Start : id 81431, Elapsed 1, Threads 8, ThreadId 6
P Start : id 29643, Elapsed 0, Threads 8, ThreadId 1
W Start : id 80940, Elapsed 1, Threads 8, ThreadId 5
P Start : id 9253, Elapsed 0, Threads 8, ThreadId 1
W Start : id 89951, Elapsed 1, Threads 8, ThreadId 8
P Start : id 53017, Elapsed 0, Threads 8, ThreadId 1
W Start : id 9253, Elapsed 22, Threads 7, ThreadId 9
P Start : id 25569, Elapsed 0, Threads 8, ThreadId 1
P Start : id 98037, Elapsed 0, Threads 8, ThreadId 1
W Start : id 53017, Elapsed 21, Threads 8, ThreadId 10
W Start : id 29643, Elapsed 22, Threads 7, ThreadId 7
// Take a look at this Elapsed this worker took 1 second to start
W Start : id 25569, Elapsed 974, Threads 9, ThreadId 11
// Take a look at this Elapsed this worker took 2 second to start
W Start : id 98037, Elapsed 1974, Threads 10, ThreadId 12
W Stop : id 28942, Elapsed 2000, Threads 10, ThreadId 4
W Stop : id 63043, Elapsed 2015, Threads 10, ThreadId 3
P Stop : id 63043, Elapsed 2016, Threads 10, ThreadId 3
P Stop : id 28942, Elapsed 2001, Threads 9, ThreadId 4
W Stop : id 81431, Elapsed 2001, Threads 8, ThreadId 6
P Stop : id 81431, Elapsed 2002, Threads 8, ThreadId 6
W Stop : id 80940, Elapsed 2002, Threads 8, ThreadId 5
P Stop : id 80940, Elapsed 2002, Threads 7, ThreadId 5
W Stop : id 89951, Elapsed 2003, Threads 6, ThreadId 8
P Stop : id 89951, Elapsed 2003, Threads 6, ThreadId 8
W Stop : id 53017, Elapsed 2022, Threads 5, ThreadId 10
P Stop : id 53017, Elapsed 2022, Threads 5, ThreadId 10
W Stop : id 9253, Elapsed 2023, Threads 5, ThreadId 9
P Stop : id 9253, Elapsed 2025, Threads 4, ThreadId 9
W Stop : id 29643, Elapsed 2024, Threads 5, ThreadId 7
P Stop : id 29643, Elapsed 2026, Threads 3, ThreadId 7
W Stop : id 25569, Elapsed 2974, Threads 2, ThreadId 11
P Stop : id 25569, Elapsed 2975, Threads 2, ThreadId 11
// eek
W Stop : id 98037, Elapsed 3975, Threads 1, ThreadId 12
// eek
P Stop : id 98037, Elapsed 4622, Threads 1, ThreadId 12

【讨论】：

您好，想知道您的 GetInfo 是什么样子的。我想对异步调用做类似的事情来衡量性能，并希望在 Elapsed 和 Threads 上获得相同的详细信息。谢谢

【解决方案2】：

Task.Yield() 将需要一些时间来等待任务调度程序中的其他异步方法，并且该时间不包含在 UnitWorkAsync 的秒表中。

代码

        private async Task UnitWorkAsync()
        {
            Stopwatch stopwatch = Stopwatch.StartNew();

            await Task.Yield();
            // Blocking call.
            //
            Thread.Sleep( 2000 );

            // Async call.
            //
            await Task.Delay( 100 );

            Console.WriteLine( "UnitWorkAsync timer: " + stopwatch.ElapsedMilliseconds );

            Interlocked.Increment( ref workItemsCount );
            //Console.WriteLine( "Work items completed: " + workItemsCount );
        }

结果

UnitWorkAsync timer: 3000
ParentWorkAsync timer: 3002
UnitWorkAsync timer: 3002
ParentWorkAsync timer: 3003
UnitWorkAsync timer: 4000
ParentWorkAsync timer: 4000
UnitWorkAsync timer: 5000
ParentWorkAsync timer: 5000
UnitWorkAsync timer: 5003
ParentWorkAsync timer: 5003
UnitWorkAsync timer: 5003
ParentWorkAsync timer: 5003
UnitWorkAsync timer: 5004
ParentWorkAsync timer: 5004
UnitWorkAsync timer: 5021
ParentWorkAsync timer: 5036
UnitWorkAsync timer: 5004
ParentWorkAsync timer: 5004
UnitWorkAsync timer: 5004
ParentWorkAsync timer: 5004
UnitWorkAsync timer: 5105
ParentWorkAsync timer: 5106
UnitWorkAsync timer: 5106
ParentWorkAsync timer: 5106
UnitWorkAsync timer: 6099
ParentWorkAsync timer: 6099
UnitWorkAsync timer: 6096
ParentWorkAsync timer: 6097

【讨论】：