could you annotate a method that should not be cal...

# coroutines

[rrva]

could you annotate a method that should not be called within a coroutine so that you get a compile-time error?

[streetsofboston]

How would that work?

Eg what if you call a regular (non-suspend) function and that function then calls that 'forbidden' method?

Curious: What use-case do you have to need such a check?

[rrva]

this method: https://github.com/open-telemetry/opentelemetry-java/blob/50408d499f85d5761d0a5ed9[…]rc/main/java/io/opentelemetry/context/ImplicitContextKeyed.java

[rrva]

it should have been annotated. I missed the javadoc

[rrva]

but yes, I guess since calling a function that calls a function would be a common issue there no way to check if you are in a coroutine context

[streetsofboston]

Ah.. ThreadLocal vs Coroutine Context Elements magic 🙂
Still, I'm not sure how you can tell the compiler when a function is called as part of a stack that has its root in a Coroutine, since regular functions can be called from Coroutines, which in turn can call your forbidden function....

[rrva]

ok, but moving to runtime, how would you warn?

[ephemient]

kotlinx-coroutines-debug has integration with BlockHound which you might be able to repurpose or copy

[Oliver.O]

Late to the party, but... indeed, tweaking BlockHound could accomplish this, although it would complain about a blocking call, not a message tailored to the special case above.

If you'd like to give it a try, you could create a BlockHoundIntegration like this (untested, but hopefully works)

import reactor.blockhound.integration.BlockHoundIntegration
import reactor.blockhound.BlockHound.Builder

class MyBlockHoundIntegration : BlockHoundIntegration {
    override fun applyTo(builder: Builder): Unit = with(builder) {
        markAsBlocking(
            "io.opentelemetry.context.ImplicitContextKeyed", "makeCurrent", "()Lio/opentelemetry/context/Scope;"
        )
    }
}

along with a service provider configuration file.

[Oliver.O]

Added caveat: The above would only work with coroutine threads marked as non-blocking. So threads from Dispatchers.Default work, while those from <http://Dispatchers.IO|Dispatchers.IO> would not detect calls.