I want to create a Dispatcher that limits concurre...

# coroutines

[basher]

I want to create a Dispatcher that limits concurrency to 1, but I don’t want the expense of creating a new thread dispatcher. Is there a way to create a limited concurrency dispatcher from the Default dispatcher?

[gildor]

There is no way (no API) for now to create a new dispatchere that reuses threads from IO or Default thread pool, only create a new thread pool and convert it to dispatcher

[gildor]

What is your use case for this?

[basher]

Maybe this isn’t the right thing, so any advice would be appreciated! I have a resource I want to access from a coroutine, but I want to make sure I don’t interact with that resource from more than one coroutine at a time. I realize I’m describing a lock, but I don’t think that’s the right primitive in coroutines. Thoughts?

[gildor]

There is non-bloking Mutex in coroutines:
https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.sync/-mutex/

[gildor]

Also Actor looks as good way to solve this, but Actors API will change, but for such simple case I think it’s fine to use it

[gildor]

Particular implementation depends on how your code should interact with this resource

[gildor]

And I think that 1 threaded Dispatcher is a bad solution for this use case or probably not a solution in general (it will work only access to resource is blocking)

[basher]

Noted! Mutex seems like a good solution for part of what I’m doing. Thanks! I may come back tomorrow with some sample code, after I think so more about the other part. Thanks again!

[hmole]

@basher Curious what's your use-case. DB transactions?

[Paul Woitaschek]

You can do Executors.newSingleThread...().asDispatcher() or sth alike

[basher]

talking about about db transactions yes, but i've recently realized it's moot

[basher]

SQLDelight mostly takes care of this

[gildor]

You can do Executors.newSingleThread...().asDispatcher() or sth alike

It's true, but in most cases it's just not needed
Also it easy to leak thread (such exector should be explicitly closed to solve problem of leaked thread)
Also it will not work with non-blocking APIs