在控制台应用程序中模拟异步死锁 [英] Simulate async deadlock in a console application
问题描述
通常，异步死锁发生在UI线程或ASP.NET上下文中.我正在尝试在控制台应用程序中模拟死锁，以便可以对库代码进行单元测试.
Usually, an async deadlock occurs in UI thread or with ASP.NET context. I'm trying to simulate the deadlock in a console application so that I can unit test my library codes.
这是我的尝试:
class Program
{
private static async Task DelayAsync()
{
Console.WriteLine( "DelayAsync.Start" );
await Task.Delay( 1000 );
Console.WriteLine( "DelayAsync.End" );
}
// This method causes a deadlock when called in a GUI or ASP.NET context.
public static void Deadlock()
{
Console.WriteLine( "Deadlock.Start" );
// Start the delay.
var delayTask = DelayAsync();
// Wait for the delay to complete.
delayTask.Wait();
Console.WriteLine( "Deadlock.End" );
}
static void Main( string[] args )
{
var thread = new Thread( () =>
{
Console.WriteLine( "Thread.Start" );
SynchronizationContext.SetSynchronizationContext( new DedicatedThreadSynchronisationContext() );
Deadlock();
Console.WriteLine( "Thread.End" );
} );
thread.Start();
Console.WriteLine( "Thread.Join.Start" );
thread.Join();
Console.WriteLine( "Thread.Join.End" );
Console.WriteLine( "Press any key to exit" );
Console.ReadKey( true );
Console.WriteLine( "Pressed" );
}
}
因此 Deadlock()应该在正确的上下文中导致死锁.为了模拟ASP.NET上下文，我使用来自 https://stackoverflow.com/a的 DedicatedThreadSynchronisationContext /31714115/121240 :
So Deadlock() should cause a deadlock in an right context. To simulate the ASP.NET context, I'm using DedicatedThreadSynchronisationContext from https://stackoverflow.com/a/31714115/121240:
public sealed class DedicatedThreadSynchronisationContext : SynchronizationContext, IDisposable
{
public DedicatedThreadSynchronisationContext()
{
m_thread = new Thread( ThreadWorkerDelegate );
m_thread.Start( this );
}
public void Dispose()
{
m_queue.CompleteAdding();
}
/// <summary>Dispatches an asynchronous message to the synchronization context.</summary>
/// <param name="d">The System.Threading.SendOrPostCallback delegate to call.</param>
/// <param name="state">The object passed to the delegate.</param>
public override void Post( SendOrPostCallback d, object state )
{
if ( d == null ) throw new ArgumentNullException( "d" );
m_queue.Add( new KeyValuePair<SendOrPostCallback, object>( d, state ) );
}
/// <summary> As
public override void Send( SendOrPostCallback d, object state )
{
using ( var handledEvent = new ManualResetEvent( false ) )
{
Post( SendOrPostCallback_BlockingWrapper, Tuple.Create( d, state, handledEvent ) );
handledEvent.WaitOne();
}
}
public int WorkerThreadId { get { return m_thread.ManagedThreadId; } }
//=========================================================================================
private static void SendOrPostCallback_BlockingWrapper( object state )
{
var innerCallback = ( state as Tuple<SendOrPostCallback, object, ManualResetEvent> );
try
{
innerCallback.Item1( innerCallback.Item2 );
}
finally
{
innerCallback.Item3.Set();
}
}
/// <summary>The queue of work items.</summary>
private readonly BlockingCollection<KeyValuePair<SendOrPostCallback, object>> m_queue =
new BlockingCollection<KeyValuePair<SendOrPostCallback, object>>();
private readonly Thread m_thread = null;
/// <summary>Runs an loop to process all queued work items.</summary>
private void ThreadWorkerDelegate( object obj )
{
SynchronizationContext.SetSynchronizationContext( obj as SynchronizationContext );
try
{
foreach ( var workItem in m_queue.GetConsumingEnumerable() )
workItem.Key( workItem.Value );
}
catch ( ObjectDisposedException ) { }
}
}
我在调用Deadlock()之前设置了上下文:
I set the context before calling Deadlock():
SynchronizationContext.SetSynchronizationContext( new DedicatedThreadSynchronisationContext() );
我希望代码可以挂在这行上，因为它应该捕获上下文:
I expect the code to hang on this line because it should capture the context:
await Task.Delay( 1000 );
但是，它通过得很好，并且程序运行到最后，并显示"Pressed".(尽管该程序挂在DedicatedThreadSynchronisationContext.ThreadWorkerDelegate()上，所以它不存在，但我认为这是一个小问题.)
However , it passes just fine and the program runs through the end, and it prints "Pressed". (Although the program hangs on DedicatedThreadSynchronisationContext.ThreadWorkerDelegate() so it doesn't exist, but I consider it a minor issue.)
为什么它不产生死锁?模拟死锁的正确方法是什么?
Why doesn't it produce a dead lock? What is the proper way to simulate a dead lock?
======================================
========================================
根据Luaan的回答，
As per the answer by Luaan,
我使用DedicatedThreadSynchronisationContext.Send()而不是创建新线程:
I used DedicatedThreadSynchronisationContext.Send() instead of creating a new thread:
Console.WriteLine( "Send.Start" );
var staContext = new DedicatedThreadSynchronisationContext();
staContext.Send( ( state ) =>
{
Deadlock();
}, null );
Console.WriteLine( "Send.End" );
它使Deadlock()在上下文中运行，因此'await'捕获了相同的上下文，因此发生了死锁.
It lets Deadlock() to run under the context, so 'await' captures the same context thus a dead lock occurs.
谢谢Lu！
推荐答案
因为死锁与同步上下文不在同一线程上运行.
Because Deadlock doesn't run on the same thread as your synchronization context.
您需要确保在同步上下文上运行 Deadlock -仅设置上下文并调用方法并不能确保做到这一点.
You need to make sure to run Deadlock on the synchronization context - just setting the context and calling a method doesn't ensure that.
最简单的修改方法是将 Deadlock 同步发送到同步上下文:
The easiest way to do this with little modification is to send the Deadlock synchronously to the synchronization context:
SynchronizationContext.Current.Send(_ => Deadlock(), null);
这给您一个延迟任务等待的不错的僵局:)
This gives you a nice deadlock on the delay task wait :)
这篇关于在控制台应用程序中模拟异步死锁的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
