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docs: clarify section on coroutine memory consumption #3225

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merged 2 commits into from Mar 31, 2022
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docs: clarify section on coroutine memory consumption #3225

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docs: clarify section on coroutine memory consumption
scolsen Mar 29, 2022
1c85bfa
docs: update coroutines-basics.md
scolsen Mar 30, 2022
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19 changes: 11 additions & 8 deletions docs/topics/coroutines-basics.md
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Expand Up @@ -245,14 +245,17 @@ Done

<!--- TEST -->

## Coroutines ARE light-weight
## Coroutines are light-weight

Run the following code:
Coroutines are less resource-intensive than JVM threads. Code that exhausts the
JVM's available memory when using threads can be expressed using coroutines
without hitting resource limits. For example, the following code launches
100000 distinct coroutines that each wait 5 seconds and then print a period
('.') while consuming very little memory:

```kotlin
import kotlinx.coroutines.*

//sampleStart
fun main() = runBlocking {
repeat(100_000) { // launch a lot of coroutines
launch {
Expand All @@ -261,19 +264,19 @@ fun main() = runBlocking {
}
}
}
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Given that the code is not runnable, I think a better choice would be to remove //sampleStart and //sampleEnd, given how they aren't recognized for code that is not runnable: https://kotlinlang.org/docs/coroutines-basics.html#coroutines-are-light-weight

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Done, thanks!

//sampleEnd
```
<!-- While coroutines do have a smaller memory footprint than threads, this
example will exhaust the playground's heap memory; don't make it runnable. -->

> You can get the full code [here](../../kotlinx-coroutines-core/jvm/test/guide/example-basic-06.kt).
>
{type="note"}

<!--- TEST lines.size == 1 && lines[0] == ".".repeat(100_000) -->

It launches 100K coroutines and, after 5 seconds, each coroutine prints a dot.

Now, try that with threads (remove `runBlocking`, replace `launch` with `thread`, and replace `delay` with `Thread.sleep`).
What would happen? (Most likely your code will produce some sort of out-of-memory error)
If you write the same program using threads (remove `runBlocking`, replace
`launch` with `thread`, and replace `delay` with `Thread.sleep`), it will
likely consume too much memory and throw an out-of-memory error.

<!--- MODULE kotlinx-coroutines-core -->
<!--- INDEX kotlinx.coroutines -->
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