C#的Async & Await筆記(2)

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既上一篇的一些觀念，來寫一些程式來實際驗證一下C#不同類型的專案上async/await跑起來會怎麼運作，執行緒會怎麼樣調用。

TL;DR，執行緒調用方式

上一篇C#的Async & Await筆記有較多的概念

這一篇的程式碼在這csharp-lab

  1. 一遇到await，執行緒不會馬上跳回到caller端，執行緒還是會往呼叫的methodAsync執行，直到最底層回傳一個Task，才開始依序跳回caller端，但如果Task已經是完成的狀態，則會省去原await機制，用原執行緒繼續執行。
  2. 一般Task不是已經完成的狀態下，遇到await，會優先看「當前」執行緒上有沒有SynchronizationContext，有則await後續的code會是原執行緒main thread來執行；沒有則await後續的code由thread pool裡面的執行緒執行。
  3. 一般Task不是已經完成的狀態下，遇到await加上ConfigureAwait(false)，則await後續的code會由thread pool裡面的執行緒執行。

執行環境

硬體

  • CPU：4 * Intel i7-6600U 2.6GHz
  • RAM： 16.0 GB
  • 系統類型： x64
  • 作業系統：Windows 10

測試的project類型與target framework

  • Console App： .NET Framework 4.6.1
  • WPF： .NET Framework 4.6.1
  • .NET Framework Web API： .NET Framework 4.6.1
  • .NET Core Web API： .NET Core 2.1.1

測試方式

  1. 寫了一個library project TestClassLibrary裡面放一個AsyncAwaitTestClass.cs，所有要跑的code都寫在裡面，可以給.NET Framework和.NET Core參照與使用
  2. 下面跑測試會個別跑，會先註解掉其他測試來讓執行測試的起始情況一致
  3. 測試有寫的四種project類型，測試上不一樣的地方主要是WPF的main thread有SynchronizationContext，其他測試上的差別只有起始thread像WPF、Console App是main thread，還是像web server是調用worker thread的差別
  4. 因為有無SynchronizationContext，基本上只會有兩種較不一樣的執行結果，下面只寫出WPF和.NET Core的結果，想執行看看都還是可以抓回去玩玩看
  5. 印出測試訊息用Debug.WriteLine寫在output讓不同的project類型都會在同一個地方印出來，會透過執行AsyncAwaitTestClass.PrintInfos印出執行的當下有多少worker threads、iocp threads、total threads，印出當下執行緒的SynchronizationContext、ManagedThreadId、IsThreadPoolThread。
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private void PrintInfos()
{
    ThreadPool.GetMaxThreads(out int maxWorkerThreads, out int maxCompletionPortThreads);
    ThreadPool.GetAvailableThreads(out int workerThreads, out int completionPortThreads);
    Debug.WriteLine(
        "  -- Worker threads: {0}, Completion port threads: {1}, Total threads: {2}",
        maxWorkerThreads - workerThreads,
        maxCompletionPortThreads - completionPortThreads,
        Process.GetCurrentProcess().Threads.Count
    );
    Debug.WriteLine(
        $"     SynchronizationContext: {SynchronizationContext.Current}\n" +
        $"     ManagedThreadId: {Thread.CurrentThread.ManagedThreadId}\n" +
        $"     IsThreadPoolThread: {Thread.CurrentThread.IsThreadPoolThread}"
    );
}

測試一：執行續一遇到await就返回呼叫端？

(1)程式碼

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private async Task RunTest1()
{
    Debug.WriteLine("===== Test 1 =====");

    Debug.WriteLine("1. === Before ReturnFinishedTaskAsync ===");
    PrintInfos();
    await ReturnFinishedTaskAsync();

    Debug.WriteLine("===== Test 1 End =====");
}

private async Task<int> ReturnFinishedTaskAsync()
{
    Debug.WriteLine("2.   === Begin MethodWithFinishedTask ===");
    PrintInfos();
    return await Task.FromResult<int>(0);
}

(1)執行結果

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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 10
     SynchronizationContext: 
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test Start =====
===== Test 1 =====
1. === Before ReturnFinishedTaskAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 10
     SynchronizationContext: 
     ManagedThreadId: 1
     IsThreadPoolThread: False
2.   === Begin MethodWithFinishedTask ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 10
     SynchronizationContext: 
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 1 End =====

不是一看到await，當前thread就跳回到caller，await裡面的code還是會先由當前thread執行，會直到執行到底層傳回task才「通常」開始一層一層返回caller。

可以在output上看到RunTest1的1.跟ReturnFinishedTaskAsync裡面的2.都是同一個thread ID，四種project結果都一樣。
其實想成下面這樣，程式是一樣的，應該就直覺async method裡面也會是同一個thread先執行。

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private async Task RunTest1()
{
    Debug.WriteLine("===== Test 1 =====");

    Debug.WriteLine("1. === Before ReturnFinishedTaskAsync ===");
    PrintInfos();
    var task = ReturnFinishedTaskAsync(); // 這裡把await分開來寫
    await task;

    Debug.WriteLine("===== Test 1 End =====");
}

測試二：await加不加ConfigureAwait(false)會發生什麼事，後續執行緒是？

(2.1)不加ConfigureAwait(false)

(2.1)程式碼

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private async Task RunTest2_1()
{
    Debug.WriteLine("===== Test 2.1 =====");

    Debug.WriteLine("1. === Before httpClient.GetStringAsync ===");
    PrintInfos();

    await httpClient.GetStringAsync(url); // without ConfigureAwait(false)

    Debug.WriteLine("2. === After httpClient.GetStringAsync  ===");
    PrintInfos();
}

(2.1)執行結果

(2.1)WPF

執行httpClient.GetStringAsync前後的code會是一樣的thread

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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 2.1 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === After httpClient.GetStringAsync  ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 28
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
(2.1).NET Core Web API

執行httpClient.GetStringAsync前後的code是不一樣的thread，後面是iocp thread

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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 23
     SynchronizationContext: 
     ManagedThreadId: 16
     IsThreadPoolThread: True
===== Test 2.1 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 23
     SynchronizationContext: 
     ManagedThreadId: 16
     IsThreadPoolThread: True
2. === After httpClient.GetStringAsync  ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 24
     SynchronizationContext: 
     ManagedThreadId: 22
     IsThreadPoolThread: True

(2.2)加ConfigureAwait(false)

(2.2)程式碼

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private async Task RunTest2_2()
{
    Debug.WriteLine("===== Test 2.2 =====");

    Debug.WriteLine("1. === Before httpClient.GetStringAsync ===");
    PrintInfos();

    await httpClient.GetStringAsync(url).ConfigureAwait(false); // with ConfigureAwait(false)

    Debug.WriteLine("2. === After httpClient.GetStringAsync ConfigureAwait(false) ===");
    PrintInfos(); // 1. and 2. would be different thread ID
}

(2.2)執行結果

(2.2)WPF
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 14
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 2.2 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 14
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 26
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
(2.2).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
===== Test 2.2 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
2. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 30
     SynchronizationContext: 
     ManagedThreadId: 12
     IsThreadPoolThread: True

(2.3)加ConfigureAwait(false)後面一定會是iocp thread？

(2.3)程式碼

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private async Task RunTest2_3()
{
    Debug.WriteLine("===== Test 2.3 =====");

    Debug.WriteLine("1. === Before ReturnFinishedTaskAsync ===");
    PrintInfos();

    await ReturnFinishedTaskAsync().ConfigureAwait(false); // with ConfigureAwait(false)

    Debug.WriteLine("3. === After ReturnFinishedTaskAsync ConfigureAwait(false) ===");
    PrintInfos();
}

(2.3)執行結果

如果跑的不是非同步IO當然不會是iocp thread

如果Task已經是完成的狀態，則會省去原await機制，用原執行緒繼續執行

(2.3)WPF
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 2.3 =====
1. === Before ReturnFinishedTaskAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2.   === Begin MethodWithFinishedTask ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
3. === After ReturnFinishedTaskAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
(2.3).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 23
     SynchronizationContext: 
     ManagedThreadId: 9
     IsThreadPoolThread: True
===== Test 2.3 =====
1. === Before ReturnFinishedTaskAsync ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 23
     SynchronizationContext: 
     ManagedThreadId: 9
     IsThreadPoolThread: True
2.   === Begin MethodWithFinishedTask ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 23
     SynchronizationContext: 
     ManagedThreadId: 9
     IsThreadPoolThread: True
3. === After ReturnFinishedTaskAsync ConfigureAwait(false) ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 23
     SynchronizationContext: 
     ManagedThreadId: 9
     IsThreadPoolThread: True

(2.4)連續兩個await呼叫有加ConfigureAwait(false)

(2.4)程式碼

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private async Task RunTest2_4()
{
    Debug.WriteLine("===== Test 2.4 =====");

    Debug.WriteLine("1. === Before httpClient.GetStringAsync ===");
    PrintInfos();

    await httpClient.GetStringAsync(url).ConfigureAwait(false); // with ConfigureAwait(false)

    Debug.WriteLine("2. === After httpClient.GetStringAsync ConfigureAwait(false) ===");
    PrintInfos();

    await httpClient.GetStringAsync(url).ConfigureAwait(false); // with ConfigureAwait(false)

    Debug.WriteLine("3. === After httpClient.GetStringAsync ConfigureAwait(false) ===");
    PrintInfos();
}

(2.4)執行結果

這邊訊息的2.跟3.有可能會是同一個iocp thread，畢竟我都對同一個URL發HTTP GET，有可能是cache導致Task很快就完成了，或是真的第二個await真的接手的thread跟第一個一樣

(2.4)WPF
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 2.4 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
3. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 12
     IsThreadPoolThread: True
(2.4).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 29
     SynchronizationContext: 
     ManagedThreadId: 15
     IsThreadPoolThread: True
===== Test 2.4 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 29
     SynchronizationContext: 
     ManagedThreadId: 15
     IsThreadPoolThread: True
2. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 30
     SynchronizationContext: 
     ManagedThreadId: 20
     IsThreadPoolThread: True
3. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 30
     SynchronizationContext: 
     ManagedThreadId: 17
     IsThreadPoolThread: True

(2.5)先呼叫一個await有加ConfigureAwait(false)，然後再呼叫一個await不加ConfigureAwait(false)？

(2.5)程式碼

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private async Task RunTest2_5()
{
    Debug.WriteLine("===== Test 2.5 =====");

    Debug.WriteLine("1. === Before httpClient.GetStringAsync ===");
    PrintInfos();

    await httpClient.GetStringAsync(url).ConfigureAwait(false); // with ConfigureAwait(false)

    Debug.WriteLine("2. === After httpClient.GetStringAsync ConfigureAwait(false) ===");
    PrintInfos();

    await httpClient.GetStringAsync(url); // without ConfigureAwait(false)

    Debug.WriteLine("3. === After httpClient.GetStringAsync ===");
    PrintInfos();
}

(2.5)執行結果

WPF的第一個httpClient.GetStringAsync有加ConfigureAwait(false)，所以await接手的會是iocp thread，可以看到2.的訊息顯示沒有SynchronizationContext，所以第二個httpClient.GetStringAsync即使沒有加ConfigureAwait(false)，後續的code也不會是main thread

(2.5)WPF
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 20
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 2.5 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 20
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 12
     IsThreadPoolThread: True
3. === After httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 11
     IsThreadPoolThread: True
(2.5).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
===== Test 2.5 =====
1. === Before httpClient.GetStringAsync ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
2. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 30
     SynchronizationContext: 
     ManagedThreadId: 12
     IsThreadPoolThread: True
3. === After httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 30
     SynchronizationContext: 
     ManagedThreadId: 12
     IsThreadPoolThread: True

(2.6)外面的沒加ConfigureAwait(false)，裡面的有加

(2.6)程式碼

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private async Task RunTest2_6()
{
    Debug.WriteLine("===== Test 2.6 =====");

    Debug.WriteLine("1. === Before MethodWithConfigureAwaitFalseInsideAsync ===");
    PrintInfos();

    await MethodWithConfigureAwaitFalseInsideAsync();

    Debug.WriteLine("4. === After MethodWithConfigureAwaitFalseInsideAsync ===");
    PrintInfos();
}

private async Task<string> MethodWithConfigureAwaitFalseInsideAsync()
{
    Debug.WriteLine("2. === Before httpClient.GetStringAsync ConfigureAwait(false) ===");
    PrintInfos();

    var result = await httpClient.GetStringAsync(url).ConfigureAwait(false);

    Debug.WriteLine("3. === After httpClient.GetStringAsync ConfigureAwait(false) ===");
    PrintInfos();

    return result;
}

(2.6)執行結果

在外層WPF因為有SynchronizationContext所以await後續還是main thread，.NET Core沒有SynchronizationContext所以裡面最後是iocp thread，外層也是iocp thread繼續

(2.6)WPF
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 2.6 =====
1. === Before MethodWithConfigureAwaitFalseInsideAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === Before httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
3. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 11
     IsThreadPoolThread: True
4. === After MethodWithConfigureAwaitFalseInsideAsync ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 28
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
(2.6).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 29
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
===== Test 2.6 =====
1. === Before MethodWithConfigureAwaitFalseInsideAsync ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 29
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
2. === Before httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 29
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
3. === After httpClient.GetStringAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 30
     SynchronizationContext: 
     ManagedThreadId: 16
     IsThreadPoolThread: True
4. === After MethodWithConfigureAwaitFalseInsideAsync ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 30
     SynchronizationContext: 
     ManagedThreadId: 16
     IsThreadPoolThread: True

(2.7)外面的有加ConfigureAwait(false)，裡面的沒加

(2.7)程式碼

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private async Task RunTest2_7()
{
    Debug.WriteLine("===== Test 2.7 =====");

    Debug.WriteLine("1. === Before MethodWithoutConfigureAwaitFalseInsideAsync ConfigureAwait(false) ===");
    PrintInfos();

    await MethodWithoutConfigureAwaitFalseInsideAsync().ConfigureAwait(false);

    Debug.WriteLine("4. === After MethodWithoutConfigureAwaitFalseInsideAsync ConfigureAwait(false) ===");
    PrintInfos();
}

private async Task<string> MethodWithoutConfigureAwaitFalseInsideAsync()
{
    Debug.WriteLine("2. === Before httpClient.GetStringAsync ===");
    PrintInfos();

    var result = await httpClient.GetStringAsync(url);

    Debug.WriteLine("3. === After httpClient.GetStringAsync ===");
    PrintInfos();

    return result;
}

(2.7)執行結果

WPF因為裡面的沒加ConfigureAwait(false)，所以await後續接手會是main thread，裡面最後執行完的是main thread，外層的有加ConfigureAwait(false)，不交由main thread執行ConfigureAwait(false)的後續，所以由worker thread接手

(2.7)WPF
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 2.7 =====
1. === Before MethodWithoutConfigureAwaitFalseInsideAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === Before httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
3. === After httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 28
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
4. === After MethodWithoutConfigureAwaitFalseInsideAsync ConfigureAwait(false) ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 28
     SynchronizationContext: 
     ManagedThreadId: 5
     IsThreadPoolThread: True
(2.7).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 31
     SynchronizationContext: 
     ManagedThreadId: 9
     IsThreadPoolThread: True
===== Test 2.7 =====
1. === Before MethodWithoutConfigureAwaitFalseInsideAsync ConfigureAwait(false) ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 31
     SynchronizationContext: 
     ManagedThreadId: 9
     IsThreadPoolThread: True
2. === Before httpClient.GetStringAsync ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 31
     SynchronizationContext: 
     ManagedThreadId: 9
     IsThreadPoolThread: True
3. === After httpClient.GetStringAsync ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 32
     SynchronizationContext: 
     ManagedThreadId: 12
     IsThreadPoolThread: True
4. === After MethodWithoutConfigureAwaitFalseInsideAsync ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 1, Total threads: 32
     SynchronizationContext: 
     ManagedThreadId: 12
     IsThreadPoolThread: True

測試三：承測試二，如果不跑在IO相關的task，而跑在Task.Delay上，後續執行緒是？

(3.1)不加ConfigureAwait(false)

(3.1)程式碼

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private async Task RunTest3_1()
{
    Debug.WriteLine("===== Test 3.1 =====");

    Debug.WriteLine("1. === Before Task.Delay ===");
    PrintInfos();

    await Task.Delay(1000);

    Debug.WriteLine("2. === After Task.Delay ===");
    PrintInfos();
}

(3.1)執行結果

(3.1)WPF
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 18
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 3.1 =====
1. === Before Task.Delay ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 18
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === After Task.Delay ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 20
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
(3.1).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
===== Test 3.1 =====
1. === Before Task.Delay ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
2. === After Task.Delay ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True

(3.2)加ConfigureAwait(false)

(3.2)程式碼

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private async Task RunTest3_2()
{
    Debug.WriteLine("===== Test 3.2 =====");

    Debug.WriteLine("1. === Before Task.Delay ConfigureAwait(false) ===");
    PrintInfos();

    await Task.Delay(1000).ConfigureAwait(false);

    Debug.WriteLine("2. === After Task.Delay ConfigureAwait(false) ===");
    PrintInfos();
}

(3.2)執行結果

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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
===== Test 3.2 =====
1. === Before Task.Delay ConfigureAwait(false) ===
  -- Worker threads: 0, Completion port threads: 0, Total threads: 19
     SynchronizationContext: System.Windows.Threading.DispatcherSynchronizationContext
     ManagedThreadId: 1
     IsThreadPoolThread: False
2. === After Task.Delay ConfigureAwait(false) ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 21
     SynchronizationContext: 
     ManagedThreadId: 5
     IsThreadPoolThread: True
(3.2).NET Core Web API
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===== Current Thread Info (in TestStart method) =====
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
===== Test 3.2 =====
1. === Before Task.Delay ConfigureAwait(false) ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True
2. === After Task.Delay ConfigureAwait(false) ===
  -- Worker threads: 1, Completion port threads: 0, Total threads: 25
     SynchronizationContext: 
     ManagedThreadId: 10
     IsThreadPoolThread: True

程式碼source code

csharp-lab