I have a function that divide and conquers a CPU-i...

# coroutines

[minisu]

I have a function that divide and conquers a CPU-intensive task using coroutines. I want to test that it actually runs concurrently in a unit test. If I were using threads, I would have called the function tasks that awaited a common CyclicBarrier. How can I achieve something similar with coroutines?

[minisu]

My current workaround is:

coroutineCounter -= 1  // a @Volatile field
yield()
assert(coroutineCounter == 0)

Seems to work, but I'm not sure if it's guaranteed to work.

[elizarov]

When you say “concurrently” what do you mean? Do you “concurrently” (as in — different pieces of code run in different coroutines) or do you mean “in parallel” (different pieces of code run in different threads)?

[minisu]

I started writing the test when fixing code that someone in my team wrote. He used runBlocking and async, but didn't realize that you have to use a suspending function. The result was that he thought things run in parallel, even though it wasn't.

[minisu]

So I guess in this case, things were neither concurrent or parallel (i.e. no coroutines and all in the same thread).

[minisu]

Ideally, I'd like to test that things are running in parallel, but I think that might be hard, so testing that it's running concurrently would be good enough.

[minisu]

Love your work btw @elizarov. It's a pleasure to work with Kotlin in the backend 🙂

[elizarov]

You can test for parallel just like in Java. Create your own executor with N thread, run a test that is supposed to do N pieces of work in parallel, then use CyclicBarrier with N parties to ensure they all indeed in different threads.

[minisu]

Thanks! You're right, I made a mistake 😐