Hi, I am developing a kotlin library to be used both from within android and/or server side jvm. Li...

# ktor

[routis]

Hi,

I am developing a kotlin library to be used both from within android and/or server side jvm.
Library needs to place some http calls, hence I user Ktor Client and give to the caller the option to customize which engine will be used.

My question is the following:
Should a wrap usages of the ktor client with withContext(<http://Dispatchers.IO|Dispatchers.IO>) { ..... } or this is not needed by ktor?

[Aleksei Tirman [JB]]

This isn't needed, because the <http://Dispatchers.IO|Dispatchers.IO> is by default.

[routis]

@Aleksei Tirman [JB] Thanks Aleksei!

Yet another dummy question: is it default to Ktor client?

[andriyo]

I had to use withContext (Io) around my Ktor client calls (okhtttp engine ) but I'm not complaining cause I like it that way :)

[Aleksei Tirman [JB]]

Yes, the client use Dispatchers.IO by default (https://github.com/ktorio/ktor/pull/3748)

[routis]

@Aleksei Tirman [JB] Thanks for your reply.
Indeed it is crystal clear now.

[andriyo]

@Aleksei Tirman [JB] it's for what version ? It doesn't look like it's in latest production release

[Aleksei Tirman [JB]]

Since 2.3.5.

[andriyo]

i see 2.3.6 branch and it doesn't show that commit https://github.com/ktorio/ktor/compare/2.3.6...main or it's not how releases are done with Ktor?

also when I use 2.3.6 client in my codebase I have to wrap client calls with withContext(IO) {} otherwise it runs network calls on Main thread on Android with OkHttp engine - am I missing something?

[Aleksei Tirman [JB]]

You can find the commit here.

[andriyo]

right so it's in main but not in 2.3.5 - do you guys release tagged main or a branch?

i just don't see that commit neither in 2.3.5 nor 2.3.6 brach. And I wouldn't care except that behavior you said is fixed - I don't see that it's fixed.
Again, sorry if it's confusion on my part - still digesting that turkey 🙂

[Aleksei Tirman [JB]]

Usually, we release from tagged main, but the few last patch releases have been released from the separate branches.

[andriyo]

anyway, what is exactly fixed? I still need to wrap my calls ktorClient.get() with withContext(IO) otherwise I get ANRs - shouldn't it not be needed after this fix?

[Javier]

@Aleksei Tirman [JB] any reason OkHttp engine is not using IO?

[Javier]

https://github.com/ktorio/ktor/blob/main/ktor-client/ktor-client-okhttp/jvm/src/io/ktor/client/engine/okhttp/OkHttpEngine.kt

[Javier]

IO was added to native in coroutines too, but ktor is not using it

[Aleksei Tirman [JB]]

For the network calls OkHttp uses its own dispatcher that uses an ExecutorService to run calls internally.

[Javier]

Based on the experience from @andriyo, looks like it is not a good default dispatcher as it generates ANRs on Android by default which is totally the opposite someone would expect from a network client and even more compared to the behavior of the rest of engines in Ktor