Task.Run(() => { ends without doing anything-CodePudding

Anyone knows why the Task.Run below just ends without doing anything, while if only keep that line:

var someDump = Helper.MakeRequest(body, Helper.GetUrl(2, ConfigurationManager.AppSettings["SomeId"]), 2);

it will work seamlessly??

Thank you!

PS: It will just print out "t2 done".

var t2 = Task.Run(() => 
{
   string filePath = System.Web.HttpContext.Current.Server.MapPath("~/"   ConfigurationManager.AppSettings["ServerPoolsFile"]);

   var someDump = Helper.MakeRequest(body, Helper.GetUrl(2, ConfigurationManager.AppSettings["SomeId"]), 2);

   JObject wfOutput = JObject.Parse(someDump.WFOutput);
   var jsonData = wfOutput["output-parameters"];
   var poolsList = jsonData[0]["value"]["string"]["value"];
   JObject siteJson = JObject.Parse(poolsList.ToString());
   filePath = filePath   "_"   siteJson["site"].ToString()   ".json";

   if (!System.IO.File.Exists(filePath))
   {
      // Create a file to write to.
      using (StreamWriter sw = System.IO.File.CreateText(filePath))
      {
         sw.WriteLine(poolsList.ToString());
      }
   }
   else
   {
      System.IO.File.WriteAllText(filePath, poolsList.ToString());
   }

}).ContinueWith(t => Console.WriteLine("t2 done."));
Task.Yield();

CodePudding user response：

You need to await the task at the end:

await t2;

Your function exits before the task had a chance to finish

CodePudding user response：

Your code creates two tasks, not just one. This code:

var t2 = Task.Run(() =>
{
    //...
}).ContinueWith(t => Console.WriteLine("t2 done."));

...is equivalent to this:

Task t1 = Task.Run(() =>
{
    //...
});

Task t2 = t1.ContinueWith(t =>
{
    Console.WriteLine("t2 done.");
});

The difference is that in the first case you don't have access to the t1 task, and so you can't await it and observe any error that may have occured. Your last chance to observe a possible error was inside the t2 body, by examining the IsFaulted/Exception property of the t argument. You didn't, so now you'll never know what happened inside the t1 task.

As a side note the ContinueWith is a primitive method, full of gotchas and nuances, and using it in application code is not advisable. If you are writing a library and you are fully aware of its nuances and pitfalls, then this advice doesn't apply. But for general usage, the async/await technology offers everything that you need for writing correct and maintainable asynchronous code.