I have a strange issue, but I am not sure if it is...

# coroutines

[Albert]

I have a strange issue, but I am not sure if it is related to coroutines. But I have the following unit test:

@Test fun testActor() {
  val testActor = actor<String> {
    println(channel.receive())
  }

  testActor.sendBlocking("CHANNEL-MESSAGE")
}

When I run this locally on my machine I see CHANNEL-MESSAGE being printed. But when I build this with docker it is never received. My Dockerfile looks like:

FROM maven:3.3.9-jdk-8
COPY . project/
WORKDIR project
RUN mvn clean package

I used version 3.3.9 which is the same on my local machine. With docker it actually freezes on the sendBlocking.
Anyone a clue how this is possible?

[gildor]

You use blocking operation.
Maybe you blocked all the threads for some reason?
Is it reproducible with such simple example?

[gildor]

Maybe you could provide some self contained example

[Albert]

Making a self contained example is difficult with this one. Because of docker and the configuration. The thing what "helped" was increasing the amount of cores in the container from 2 (default) to 3 (on Windows).

[gildor]

I think you blocked all the threads of common pool and no more threads to dispatch coroutines

[Albert]

But then it is still unclear to me why it is happening in docker only. when I do this on my host exactly the same way it works

[gildor]

Because on your host you just have more available threads in CommonPool. CommonPool is cpuNum - 1

[gildor]

But, I do not exclude that there is still some bug, this is why I asked self contained example

[gildor]

No need to set amount of cores for docker, you can instead set system property kotlinx.coroutines.default.parallelism to set minimal amount of threads in commonpool

[gildor]

also you can try to use new experimantal dispatchers, that can handle such cases automatically and start additional threads if all of existing are blocked

[gildor]

actually with 2 cores you have only 1 thread in CommonPool