Maybe this is a stupid question but I am somewhat ...

# coroutines

[Michael Paus]

Maybe this is a stupid question but I am somewhat puzzled by the following result of a test.
I am testing a suspend function with the following structure.

val ioDispatcher: CoroutineDispatcher = <http://Dispatchers.IO|Dispatchers.IO>

suspend fun doSomething(ioDispatcher: CoroutineDispatcher) {
   withContext(ioDispatcher) {
      println("With context $ioDispatcher is running on ${getCurrentThreadName()}")
   }
}

When I run the test and pass the defined ioDispatcher to the function doSomething the print statement results in the following output:

With context <http://Dispatchers.IO|Dispatchers.IO> is running on DefaultDispatcher-worker-5 @coroutine#18

Why is this running on a DefaultDispatcher worker and not on an IODispatcher worker?

[Alexandru Caraus]

On what dispatcher does it run before and after withContext?

[Michael Paus]

I haven’t specified any. I run the test from IntelliJ via Gradle and the test function just calls runBlocking().

[Joffrey]

These dispatchers share threads, for optimisation purposes. When switching from default to IO, it might not actually change threads

[PHondogo]

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-dispatchers/-i-o.html

[PHondogo]

Read last section

[Michael Paus]

Thanks a lot, that explains the behaviour. I already thought all my code is wrong 😉.