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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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20 changes: 12 additions & 8 deletions docs/topics/coroutines-basics.md
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Expand Up @@ -245,35 +245,39 @@ 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
('.'):
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Suggested change
('.'):
('.'), all the while consuming very little memory:

Or something in this vein. Otherwise, the whole point is obscured.

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Good point! Added.


```kotlin
import kotlinx.coroutines.*

//sampleStart
fun main() = runBlocking {
//sampleStart
repeat(100_000) { // launch a lot of coroutines
launch {
delay(5000L)
print(".")
}
}
}
//sampleEnd
}
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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!

```
{kotlin-runnable="true" kotlin-min-compiler-version="1.3"}
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This would go against our narrative :)
Try running https://play.kotlinlang.org/#eyJ2ZXJzaW9uIjoiMS42LjEwIiwiY29kZSI6ImltcG9ydCBrb3RsaW54LmNvcm91dGluZXMuKlxuLy9zYW1wbGVTdGFydFxuZnVuIG1haW4oKSA9IHJ1bkJsb2NraW5nIHtcbi8vc2FtcGxlU3RhcnRcbiAgICByZXBlYXQoMTAwXzAwMCkgeyAvLyBsYXVuY2ggYSBsb3Qgb2YgY29yb3V0aW5lc1xuICAgICAgICBsYXVuY2gge1xuICAgICAgICAgICAgZGVsYXkoNTAwMEwpXG4gICAgICAgICAgICBwcmludChcIi5cIilcbiAgICAgICAgfVxuICAgIH1cbn1cbi8vc2FtcGxlRW5kIiwicGxhdGZvcm0iOiJqYXZhIiwiYXJncyI6IiJ9
However lightweight coroutines are, they still take some memory, more that our playground allocates.

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ah, I figured something like this might be the case--I added a comment noting as much so that future contributors don't make the same mistake, I felt there was probably a good reason for this one not being runnable but didn't see any immediate indication as to why, thus the PR--thanks for letting me know!


> 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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