Are all requests coming to an ktor application han...

# ktor

[Hong Phuc]

Are all requests coming to an ktor application handled on the same Application's coroutine? Since when I print out the CoroutineContext when a request hit an endpoint I get the same context. Thanks in advance

[simon.vergauwen]

The Application doesn't run inside a coroutine, but is a CoroutineScope that has a SupervisorJob. This Job has an optional parent which can be supplied through embeddedServer, but if using EngineMain it's always null.

The Routing plugin has another CoroutineScope which is a child of the Application scope. Most engines don't run in a coroutine (except CIO), but they create a new coroutine for every request that is being handled.

So every coroutine that is created to handle a request is a grandchild of the Application scope, and a child of the Routing scope.

Depending on how you print the CoroutineContext you will indeed always see the same thing. For Netty: https://github.com/ktorio/ktor/blob/828e6978166adf2ed73a01702d57958372d3dc4b/ktor-[…]er-netty/jvm/src/io/ktor/server/netty/NettyApplicationEngine.kt

[e5l]

fyi @Viktoriya Nikolova

[Hong Phuc]

Thanks for the info, @simon.vergauwen. I think it would be beneficial if the fact that "a new coroutine is created for every request that is being handled" is stated in the official docs, for situation like a singleton object which being shared between different request-handler functions, can cause the code to be racy since likely that it's being shared between different threads. What do you think

[simon.vergauwen]

Yes, absolutely. We're working on a tutorial explaining in detail how coroutines work in Ktor, this will be released soon-ish during the summer. I am giving a lighting talk @ KotlinConf on this topic as well, you can catch it on the livestream or afterwards.

Later in the year I hope to give a longer talk on this topic as well, or perhaps in a webinar.

[Hong Phuc]

Nice! Anw I might as well just open a pr to add that line to the doc later (assuming that no one is already on it yet). Thanks again, Simon