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Clarify the guarantees on the number of IO threads #4578

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dkhalanskyjb merged 2 commits into from
Dec 18, 2025
+13 −7
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Clarify the guarantees on the number of IO threads #4578

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677710c
Clarify the guarantees on the number of IO threads
dkhalanskyjb Dec 1, 2025
11cbc0f
Improved wording
dkhalanskyjb Dec 8, 2025
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6 changes: 4 additions & 2 deletions kotlinx-coroutines-core/jvm/src/Dispatchers.kt
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Expand Up @@ -57,8 +57,10 @@ public actual object Dispatchers {
* dispatcher typically does not lead to an actual switching to another thread. In such scenarios,
* the underlying implementation attempts to keep the execution on the same thread on a best-effort basis.
*
* As a result of thread sharing, more than 64 (default parallelism) threads can be created (but not used)
* during operations over IO dispatcher.
* Whenever we are talking about the number of IO threads in the pool being limited by some number,
* that only means that at most that many threads are going to *actually perform* IO work in parallel.
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@murfel murfel Dec 1, 2025

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Possibly make it more formal, by getting rid of "we"

"The number of IO threads is at most N" means that at most N threads...

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@dkhalanskyjb dkhalanskyjb Dec 8, 2025

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I liked your suggestion in principle, but didn't think of a way to clearly incorporate it, so I reworded the KDoc to improve accuracy. Since this is an extensive change, please take a look again.

* It is still possible to observe more threads than that, but those threads are guaranteed to be in their
* start-up or shutdown phases.
*/
@JvmStatic
public val IO: CoroutineDispatcher get() = DefaultIoScheduler
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