<@U0BLPSJAK> What is this reference to `copyToSuspend` @ <https://ktor.io/servers/uploads.html> ? I ...

# ktor

[rocketraman]

@Deactivated User What is this reference to copyToSuspend @ https://ktor.io/servers/uploads.html ? I suspect that should just be copyTo right?

[Deactivated User]

Well. It is just an extension method defined below in that page too. I guess I added the suspend suffix to make it clear that was asynchronous. But I probably i could just remove that suffix

[rocketraman]

Ah, I didn't even see that... I thought it wasn't really possible to create a suspending function reading/writing streams, as streams are always blocking. There was some discussion about this in #coroutines .

[rocketraman]

i.e. there is no way to guarantee that that call to out.write(buffer, 0, bytes) will not block.

[Deactivated User]

Actually, that extension method does the blocking calls in another thread. So yes, it is blocking, but it blocks another thread.

[rocketraman]

Via the ioCoroutineDispatcher?

[Deactivated User]

Yes. That dispatcher uses a thread pool just for blocking I/O

[rocketraman]

Cool. I didn't realize that was already available -- I thought it was still being worked on.

[Deactivated User]

And it makes copy in chunks. So after each suspension, for each thread in that dispatcher, it can multiplex other synchronous reads

[rocketraman]

Hmm, the issue is still open... https://github.com/Kotlin/kotlinx.coroutines/issues/79

[rocketraman]

Ah, I see IOCoroutineDispatcher is part of ktor, not the couroutines lib.

[rocketraman]

Cool stuff, thanks.

[Deactivated User]

https://github.com/ktorio/ktor/blob/c8dd6d606f15c4f2fca9bac86dfd45190bdb2579/ktor-network/src/io/ktor/network/util/Pools.kt#L12

https://github.com/ktorio/ktor/blob/c8dd6d606f15c4f2fca9bac86dfd45190bdb2579/ktor-network/src/io/ktor/network/util/IOCoroutineDispatcher.kt

[Deactivated User]

yes