ToListAsync() 根本没有完成 [英] ToListAsync() does not complete at all

问题描述

我想异步执行一些查询.但是当我通过代码进行调试时，大多数时候调用 ToListAsync() 时程序会停止.没有可见的异常，并且调用堆栈窗口被清除.当我在 VS 中按下暂停按钮时，我可以看到调用当前方法之前的堆栈帧.

I want to execute some queries async. But when I debug through the code, most times when an ToListAsync() is called the program stops. There is no visible exception, and the callstack window is cleared. When I press the pause button in VS, I can see the stack frame just before the current method was called.

var res1 = await context.Address().Where(...).ToListAsync();
var res2 = await context.Person().Where(...).ToListAsync();
var res3 = await context.Rule().Where(...).ToListAsync();

有时第一个调用有效，在极少数情况下第二个调用也有效.但至少在第三次调用时程序停止了.我完全不知道为什么......

Sometimes the first call works, in rare cases the second too. But at least at the third call the program stops. I have absolutely no clue why...

推荐答案

来自评论:

这是一个 wpf 应用程序.这些命令在异步方法中.我使用 var result = LoadAsync.Result();

It is a wpf application. The commands are within an async method. I call this from a non-async method using var result = LoadAsync.Result();

就在那里，这是一个僵局.DispatcherSynchronizationContext 尝试将延续(第一个 await 之后的所有内容)编组回调度程序 (UI) 线程，该线程当前被调用 LoadAsync.Result

Right there, thats a deadlock. The DispatcherSynchronizationContext tries to marshal the continuation (everything after the first await) back onto the dispatcher (UI) thread, which is currently blocked by the call to LoadAsync.Result

解决办法:

1. await 在调用堆栈的顶部，通过使您的方法返回 async Task 而不是使用 Task.Result:

1. await at the top of your call stack by making your method return an async Task instead of using Task.Result:

await LoadAsync();

如果您绝对不能将堆栈顶部的方法更改为 async Task 并且由于某些不明原因仍然必须调用 Task.Result，使用 ConfigureAwait(false) 在等待你的内部异步方法时.这将告诉同步上下文明确不尝试将工作编组回调度程序线程:

If you absolutely cant change the method at the top of of the stack to async Task and for some obscure reason have to still call Task.Result, use ConfigureAwait(false) when awating your inner async methods. This will tell the sync context to explicitly not attempt to marshal work back to the dispatcher thread:

var res1 = await context.Address().Where(...).ToListAsync().ConfigureAwait(false);
var res2 = await context.Person().Where(...).ToListAsync().ConfigureAwait(false);
var res3 = await context.Rule().Where(...).ToListAsync().ConfigureAwait(false);        

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