1) Why does this code produce random results? Eith...

# coroutines

[Jan Skrasek]

1) Why does this code produce random results? Either 3A or 1A\n3A
2) Why it never produce 2B?
3) Why without conflate() it gives also random results?
4) Why without conflate() it returns sometimes 2B?


Link for playground: https://play.kotlinlang.org/#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

Untitled

[tseisel]

Both conflate and combine internally use channels to buffer elements, launching a new coroutine to collect elements from upstream.
In your case, neither consumer nor producer are slow so results are quite random (depends on what coroutine resumes first).
Try to introduce delays after conflate (for example, in the body of combine) and in you'll see that results becomes determinictic.

[Marko Mitic]

not a expert but I can give it a try:
1) race condition as conflated flows are collected on separate coroutine
2) it's unlikely to produce it as elements from flow1 are emitted in short span and collector always gets the most recent value emitted. This also explains 1A/n3A and 3A results - if flow1 emits first you'll get 3A and if flow2 is faster, it will wait for first element to be emitted from flow2, miss second one and get last emitted - 3

[tseisel]

I agree this is quite confusing : I'd expect that without conflate, it would always emit 1A 2A 3A

[Marko Mitic]

In 1.3.0RC combine was named combineLatest which better describes the behavior

[Jan Skrasek]

Thank you for pointing out the channel - combine uses it internally and therefore it doesn't work even without conflate.