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.netasync-awaittask-parallel-library
Mr. Boy
Mr. Boy

Reputation: 63728

What happens if you call a blocking method within an async call?

If you are making an aysnc-enabled application, and you have to interact with a 3rd-party library which only provides blocking methods, what happens when an async method blocks?

An easy example would be in .Net Framework, Socket.Receive lets you set a timeout but then blocks. If a 3rd-party lib wraps this and I call it within an asyncronous methoddoes it simply mean whichever thread the runtime assigns to the Task is blocked? Could it block other tasks or have other side-effects?

Upvotes: 0

Views: 1207

Answers (2)

Arman Ebrahimpour
Arman Ebrahimpour

Reputation: 4461

If a 3rd-party lib wraps this and I call it within an asyncronous methoddoes it simply mean whichever thread the runtime assigns to the Task is blocked?

Yes. At best it blocks your task thread and at worst if you were in any Synchronization Context (Desktop GUI or ASP.NET Request Threads before .Net Core) you'll be stuck in deadlock!

Could it block other tasks or have other side-effects?

If you wrap blocking method by thread named T which is defined like Task.Run(/* Blocking method */) it will block T.

Upvotes: 1

Nick
Nick

Reputation: 5042

There is nothing wrong to block in an async method. There are implications, though.

If you block in an async void method, which is invoked by an UI event, you will also block the UI thread and make your UI unresponsive.

When you block in a async Task method, or in any Task you will of course block the thread that currently runs this part of the method or this task. If you run concurrently many instances of this task, or if your method gets executed concurrently (for example, it is a service method that gets called by many clients), you can exhaust the thread-pool. This can prevent other tasks from running, or other clients to call your service.

If you want to avoid the latter case, it might be worthy to run this blocking method in a long-running Task. The current implementation in .Net will create a separate thread for this task, thus not blocking a thread from the thread pool.

Upvotes: 1

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