C＃使用Async在继续关闭主类的同时在单独的线程中运行函数

Question

I am trying to create an application for learning purposes going along with an Async in C# book. However I am having trouble implementing the ideas in the form of which i want. Please let me know if this is doable or not.

Basically, I have a console application with 3 classes. The user inputs some data on the console and then I have a class which executes a SQL command/query and creates a datatable. However the queries actually take quite a bit of time depending on the time of day so this is what I Want: I want to run the class/function which executes my sql query, executes some code right below it in the main program, and then wait for the sql query/data table to finish. After this I then do an export to excel. A portion of the code is below, but what I am having trouble with is the syntax for the async command. I tried making a task which indicates the calling of the sql query function but i get a compiler error saying it cannot convert the type into a task. Is there a way to do this by assigning my createReport function as a task and then awaiting for it to complete later on?

 if (Regex.IsMatch(Number,@"^\d+$") && Number.Length <= 3)
        {

      reportCreate.createReport(detailLength,detailDate,detailNumber);

   /* ^^ This was my original syntax but I want to make this asynchronous or in 
   a separate thread so I can continue working below.*/ 

   // do some comparing work here while the sql query/datatable is running.

   /* Wait for the datatable thread to finish and then continue with the code 
    below. Is there a way to do this using task and await? */ 



          }

Answer 1

You could do this by making your work run in the background and awaiting the results, ie:

var task = Task.Run(()=>reportCreate.CreateReport(...));

// Do other work

var report = await task;

That being said, this will only work if the CreateReport method is fine working on a background thread.

Also - be aware that async in a console application often behaves oddly, as there is no synchronization context to post back onto. This means that special care needs to be taken if you want to guarantee that things work properly. A simple way to handle this is to not use async/await, but instead just wait on the result:

var task = Task.Run(()=>reportCreate.CreateReport(...));

// Do other work

var report = task.Result; // Will block until first task is done

Answer 2

The first thing i would advise you is to look if your ORM provider (Entity Franework, ADO.NET, etc) provides an async endpoint. If it does, you wont be needing the extra thread creation, as database work is primarily IO bound.

If it doesn't and you to execute this on a different thread, you may use the Task Parallel Librarys Task class to execute work on a ThreadPool thread:

if (Regex.IsMatch(Number,@"^\d+$") && Number.Length <= 3)
{
    var createReportTask = Task.Run(() => { reportCreate.createReport(detailLength,detailDate,detailNumber }));

    // do some comparing work here while the sql query/datatable is running.

    await createReportTask;
}

Note that when using this in a Console Application you have to make sure your Main method doesn't return, hence terminating you process.

I strongly advise you to look for true asynchronous endpoints, those which dont require using a new thread at all.