在控制台应用程序中调用HttpClient.GetAsync-死锁

Question

I searched and saw many posts and I don't know why this simple console call using httpclient.getasync and awaiting it causes it not to complete. here is the code:

using System;
using System.Net.Http;
using System.Threading.Tasks;

public class Program
{
    public static void Main(string[] args)
    {
        GetAPI().Wait();
        Console.WriteLine("Hello");
        //Console.ReadLine();
    }

    public static async Task GetAPI()
    {
        using (HttpClient client = new HttpClient())
        {
            var response = await client.GetAsync("https://www.google.com/");
            //var response = client.GetAsync("https://www.google.com/").Result

            string content = await response.Content.ReadAsStringAsync();
            Console.WriteLine(content);
        }
    }
}

If I change to use client.GetAsync(" https://www.google.com/ ").Result; and remove "await" (see commented out code) it will work however I believe that is a no no because I am making an asynchronous function into synchronous. I've seen other posts and blogs about this and it all claims what I am trying to do is correct but when running the example app it just doesn't turn out that way.

Answer 1

The issue is that awaiting the client.GetAsync, after getting the result is waiting for main thread to be free and main thread is waiting for client.GetAsync to complete.

       var response = await client.GetAsync("https://www.google.com/").ConfigureAwait(false);
       string content = await response.Content.ReadAsStringAsync().ConfigureAwait(false);

Will tell that client.GetAsync to complete on other thread and then return the result back to main thread so that no more dead lock.

Answer 2

You can call wait() in Main .

But be carefull, this only works in console applications and will dead lock in UI applications like ASP.NET, WPF, WinForms...

public void Main(string[] args)
{

    try
    {           
         var t =  GetAPI();
         t.Wait();
         Console.WriteLine(t.Result);   
    }
    catch (Exception ex)
    {
         Console.WriteLine(ex.Message);  
    }

}

public static async Task<string> GetAPI()
{
   using (HttpClient client = new HttpClient())
   {
      var response = await client.GetAsync("https://www.google.com/"); 
      string content = await response.Content.ReadAsStringAsync(); 

     return content;
   }
}

MSDN

This code will work just fine in a console application but will deadlock when called from a GUI or ASP.NET context.