Hi there, `limitedParallelism` in 1.6.0 looks very promising. One question that jumped immediately t...

# coroutines

[uli]

Hi there, limitedParallelism in 1.6.0 looks very promising. One question that jumped immediately to my mind: Is this feature recursive? i.e. let’s say I have 2 endpoints I want to serve and I want to limit thread usage to 64 overall, but only allow 50 threads per endpoint. Would the following code do that?

val overallIODispatcher = Dispatchers.IO.limitedParallelism(64)
val endpoint1Dispatcher = overallIODispatcher.limitedParallelism(50)
val endpoint2Dispatcher = overallIODispatcher.limitedParallelism(50)

[bezrukov]

yes, it is.
However, Dispatchers.IO has special implementation for limitedParallelism , so if you will use <http://Dispatchers.IO|Dispatchers.IO> directly, you may end up with 128 threads.
See https://github.com/Kotlin/kotlinx.coroutines/issues/2943 for more details

[Vsevolod Tolstopyatov [JB]]

Would the following code do that?

Yes, this is exactly the intended way.

if you will use <http://Dispatchers.IO|Dispatchers.IO> directly, you may end up with 128 threads.

If you meant the pattern like

val endpoint1Dispatcher = Dispatchers.IO.limitedParallelism(50)
val endpoint2Dispatcher = Dispatchers.IO.limitedParallelism(50)

Then the number of threads can be as high as 100 (as long as Dispatchers.IO is not used anywhere else). Though all these threads will be created lazily on demand

[bezrukov]

(as long as Dispatchers.IO is not used anywhere else)

yep, I meant this ☝️ that using IO dispatcher anywhere else may lead to spawn 64 more threads

[uli]

No. I meant

val endpoint1Dispatcher = overallIODispatcher.limitedParallelism(50)
val endpoint2Dispatcher = overallIODispatcher.limitedParallelism(50)

i.e. using an already limited dispatcher as host

The question is, will endpoint1Dispatcher + endpoint2Dispatcher together be limited to 64 threads, as this is what their host overallIODispatcher is limited to?

[Vsevolod Tolstopyatov [JB]]

Yes, they will be limited to 64 threads in total

[uli]

After reading again, I guess the answer is already in your comments above. So it is, Yes it does exactly what you want. But note Dispatcher.IO as a host for limitedParallelism itself is unlimited.

[uli]

And I guess the fix has been forward ported to Pannenhilfe StaticContentActivity (by accident?)