为什么调用方方法和异步方法具有相同的线程id

本文关键字：id 线程 异步方法 方方法 调用 方法 为什么 | 更新日期: 2023-09-27 18:29:15

请参阅下面的代码。

public MainViewModel()
    {
        LongRunningOperationCommand = new RelayCommand(ExecuteLongRunningOperationCommand);
    }
    private void ExecuteLongRunningOperationCommand()
    {
        Test();
    }
    private async Task Test()
    {
        Log += "Command begin: " + DateTime.Now + "'r'n";
        Log += "Command thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
        var getStringAsync = GetStringAsync();
        Log += "Work in Command...'r'n";
        Log += "Work in Command which not related to the result of async method will complete: " + DateTime.Now + "'r'n";
        Log += "Work in Command which not related to the result of async method will complete, thread: " +
               Thread.CurrentThread.ManagedThreadId + "'r'n";
        string result = await getStringAsync;
        Log += "Command will complete: " + DateTime.Now + "'r'n";
        Log += "Command will complete, thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
        Log += result + "'r'n";
    }
    private async Task<string> GetStringAsync()
    {
        Log += "Async method begin: " + DateTime.Now + "'r'n";
        Log += "Async method thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
        Log += "Work in Async method... 'r'n";
        await Task.Delay(10000);
        Log += "Async method will complete: " + DateTime.Now + "'r'n";
        Log += "Async method will complete, thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
        return "GetStringAsync method completed!";
    }

结果如下

Command begin: 1/6/2016 11:58:37 PM
Command thread: 8
Async method begin: 1/6/2016 11:58:37 PM
Async method thread: 8
Work in Async method... 
Work in Command...
Work in Command which not related to the result of async method will complete: 1/6/2016 11:58:37 PM
Work in Command which not related to the result of async method will complete, thread: 8
Async method will complete: 1/6/2016 11:58:47 PM
Async method will complete, thread: 8
Command will complete: 1/6/2016 11:58:47 PM
Command will complete, thread: 8
GetStringAsync method completed!

GetStringAsync方法中等待Task.Delay之后的线程id应与之前不同。为什么结果是一样的？在Console应用程序中，线程ID是不同的，但在WPF应用程序中它们是相同的。有人能帮忙吗？

为什么调用方方法和异步方法具有相同的线程id

async/await的一个要点是，如果你有一个SynchronizationContext，比如WPF的DispatcherSynchronizationContext，那么在等待之后，在该线程上开始的工作将继续在该线程中进行，除非你告诉它不要这样做。

控制台应用程序没有SynchronizationContext，因此它使用默认上下文来调度线程池上的线程，这就是为什么您可以看到与WPF和控制台应用程序不同的行为。

为了告诉async/await它不需要保持在相同的同步上下文上，您可以在等待时使用.ConfigureAwait(false)，如果需要，它将使用默认的线程池上下文进行回调。

private async Task Test()
{
    Log += "Command begin: " + DateTime.Now + "'r'n";
    Log += "Command thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
    var getStringAsync = GetStringAsync();
    Log += "Work in Command...'r'n";
    Log += "Work in Command which not related to the result of async method will complete: " + DateTime.Now + "'r'n";
    Log += "Work in Command which not related to the result of async method will complete, thread: " +
           Thread.CurrentThread.ManagedThreadId + "'r'n";
    string result = await getStringAsync.ConfigureAwait(false);
    Log += "Command will complete: " + DateTime.Now + "'r'n";
    Log += "Command will complete, thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
    Log += result + "'r'n";
}
private async Task<string> GetStringAsync()
{
    Log += "Async method begin: " + DateTime.Now + "'r'n";
    Log += "Async method thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
    Log += "Work in Async method... 'r'n";
    await Task.Delay(10000).ConfigureAwait(false);
    Log += "Async method will complete: " + DateTime.Now + "'r'n";
    Log += "Async method will complete, thread: " + Thread.CurrentThread.ManagedThreadId + "'r'n";
    return "GetStringAsync method completed!";
}

注意，执行.ConfigureAwait(false)并不能保证其余代码将在线程池中，如果任务处于Completed状态，则代码将同步执行，并停留在最初称为await的任何线程上。

有关更多信息，请参阅文章"It’s All About the SynchronizationContext"。

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