为什么此异步/等待代码不会死锁

Question

I am reading this article about deadlock, and I tried with my own code and it doesn't have deadlock issue. Why is that?

I am expecting:

1. GetJsonAsync finishes await and about to return jsonString

2. Main is executing jsonTask.Result and hold the context

3. GetJsonAsync wants to return jsonString until context is available

4. deadlock will happen

     public static void Main(string[] args) { var jsonTask = GetJsonAsync(); int i = jsonTask.Result; Console.WriteLine(jsonTask.Result); } public static async Task<int> GetJsonAsync() { var jsonString = await ReturnIntAsync(); return jsonString; } public static async Task<int> ReturnIntAsync() { int i = 0; await Task.Run(() => i++); return i; } 

Answer 1

It doesn't deadlock because there's no synchronizing SynchronizationContext , so the async method resumes executing on a thread pool thread, not the main thread.

Relevant quotes from the article (emphasis added):

Here's the situation: remember from my intro post that after you await a Task, when the method continues it will continue in a context.

In the first case, this context is a UI context (which applies to any UI except Console applications ). In the second case, this context is an ASP.NET request context...

For the UI example, the “context” is the UI context; for the ASP.NET example, the “context” is the ASP.NET request context. This type of deadlock can be caused for either “context”.

If you really want to deadlock a Console application this way, you can use AsyncContext from my AsyncEx library to install a single-threaded context on the main thread of your Console app.