“Is it secret Frodo? Is it SAFE?” So I have this p...

# coroutines

[pajatopmr]

“Is it secret Frodo? Is it SAFE?” So I have this piece of code (first serious coroutine hacking I’ve done) where I have a map associating names with lists of data. The main thread will allow clients to access the lists while a daily background thread will update the data. Main thread is read-only, Background thread is write-only. I think, from an app perspective, that this code is safe even if not predictable. So am I correct?

[octylFractal]

only threadsafe if data is thread safe, I think. if data is accessed concurrently with a non-thread-safe-map like HashMap, it's likely to to throw ConcurrentModificationException or worse, fail silently.

reason being is that you are accessing data on two threads, the <http://Disp.IO|Disp.IO> threads and your main threads. even if it's not writing on both, it's still problematic for HashMap.

[octylFractal]

https://kotlinlang.org/docs/reference/coroutines/shared-mutable-state-and-concurrency.html

[marstran]

You should share the data by communicating, not by sharing mutable data. I think you should use an actor.

[pajatopmr]

@marstran do you have a link handy?

[marstran]

You could check out Roman's talk from Kotlinconf last year:

https://www.youtube.com/watch?v=a3agLJQ6vt8▾

[octylFractal]

https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/actor.html for current API, to be phased out

[pajatopmr]

And I just came across actor in the link @octylFractal sent.

[marstran]

@octylFractal Yes, but there will be a replacement. Actors as a concept is not obsolete.

[octylFractal]

mhm. I only meant the specific API point

[pajatopmr]

Yes, it is very clear from https://github.com/Kotlin/kotlinx.coroutines/issues/87 that the actor model is useful but could be better (support a more complex model). So it looks like a decent choice to fix my issue.

[elizarov]

Sharing MutableMap in this way is not safe.