ToListAsync（）未完成所有 [英] ToListAsync() does not complete at all

问题描述

我要执行一些查询异步。 但是，当我在code调试，大多数时候一个ToListAsync（）被调用的程序停止。 没有可见的异常，并调用堆栈窗口被清除。 当我preSS在VS暂停按钮，我可以看到当前的方法被调用之前堆栈帧。

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();

有时候第一次调用工作，在极少数情况下，第二个了。 但是至少在第三调用的程序停止。 我绝对不知道为什么...

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

从注​​释：

这是一个WPF应用程序。该命令是一个异步方法中。我用把这种从一个非异步方法 VAR的结果= 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，那是一个僵局。该<一href="http://msdn.microsoft.com/en-us/library/system.windows.threading.dispatchersynchronizationcontext(v=vs.110).aspx"><$c$c>DispatcherSynchronizationContext试图编组的延续（一切后，第一个计谋）返回到调度器（UI）线程，这是目前被调用封杀 LoadAsync。结果

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

解决方法：

1. 等待在你调用堆栈的顶部通过你的方法返回，而不是一个异步任务使用 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();

如果你绝对不能在堆栈的顶部异步任务改变方法对于一些模糊的原因有还叫 Task.Result ，使用<一个href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.task.configureawait(v=vs.110).aspx"><$c$c>ConfigureAwait(false) awating你内心的异步方法时。这将告诉同步上下文明确不尝试元帅的工作回调度线程：

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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