CODEWITHSUNDEEP
c#asp.netasynchronousasync-awaittask-parallel-library
Liam
Liam

Reputation: 29634

async library calls relying on each other and how to handle?

this is a follow on from a previous question I posted Calling an async method using a Task.Run seems wrong?

I thought the code written by the contractor was wrong but following on from the answers provided I'm now wondering if it's the libraries fault. This library exposes two methods that I need to use. One returns a "template" and one consumes part of this template (it does in my implementation anyway). But both are async methods returning Tasks.

To explain my library has methods:

public Task<TemplateInfo> TemplateInfo(TemplateInfoRequest request);
public Task<List<EmailResult>> SendMessageTemplate(SendMessageTemplateRequest request);

I need to call these thus:

public bool SendMessage()
{
  var template = TemplateInfo(...);
  var message = //use template to create message
  var sendResponse = SendMessageTemplate(message);

   return sendResponse.Count > 0;
}

So the second call relies on the first. This is where the async doesn't make sense to me. I can't and don't want to run these in parallel. I want to run them in sequence. I want my method to by synchonous.

An answer in my previous question also states:

Since you're blocking on an async method (which you shouldn't do) there is a chance you'll deadlock.

So how do I access these async methods in such a way that they are processed in turn and return a synconhonous result but do not cause deadlocks?

Upvotes: 1

Views: 328

Answers (1)

i3arnon
i3arnon

Reputation: 116518

Async doesn't (necessarily) means parallel.

You can call both async method sequentially without them running in parallel. Simply call the first and await the returned task and then do the same with the second.

var template = await TemplateInfo(...);
var message = //use template to create message
var sendResponse = await SendMessageTemplate(message);

This is still useful compared to synchronous code because while the asynchronous operation is "running" there's no thread needed and so your threads can go work on other parts of your application.

If you would call both and only then await the returned tasks you will (maybe) run in parallel:

var templateTask = TemplateInfo(...);
var sendResponseTask = SendMessageTemplate(message);
await templateTask;
await sendResponseTask;

Upvotes: 5

Related Questions