Application.kt

package com.example

import io.ktor.server.application.*
import io.ktor.server.response.*
import io.ktor.server.routing.*
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.asContextElement
import kotlinx.coroutines.delay
import kotlinx.coroutines.withContext
import org.jetbrains.exposed.sql.transactions.TransactionManager
import org.jetbrains.exposed.sql.transactions.experimental.newSuspendedTransaction
import kotlin.random.Random


val threadLocal = ThreadLocal<String>()

fun Application.configureRouting() {
    routing {
        get("/") {
            require(TransactionManager.currentOrNull() == null) { "1 - transaction should not exist at the start" }
            newSuspendedTransaction {
                require(TransactionManager.currentOrNull() != null) { "2 - transaction should exist now" }
                delay(200)
                require(TransactionManager.currentOrNull() != null) { "3 - transaction should exist after resume" }
            }
            require(TransactionManager.currentOrNull() == null) { "4 - transaction should not exist at the end" }
            call.respondText("Hello World!")
        }

        get("/foo") {
            require(threadLocal.get() == null) { "1 - thread local should not exist at the start" }
            withContext(threadLocal.asContextElement(Random.nextInt(100).toString())) {
                require(threadLocal.get() != null) { "2 - thread local should exist now" }
                delay(200)
                require(threadLocal.get() != null) { "3 - thread local should exist after resume" }
            }
            require(threadLocal.get() == null) { "4 - thread local should not exist outside the withContext" }
            call.respondText("Hello World!")
        }

        // With Dispatchers.IO
        get("/bar") {
            require(threadLocal.get() == null) { "1 - thread local should not exist at the start" }
            withContext(
                Dispatchers.IO +
                        threadLocal.asContextElement(Random.nextInt(100).toString())
            ) {
                require(threadLocal.get() != null) { "2 - thread local should exist now" }
                delay(200)
                require(threadLocal.get() != null) { "3 - thread local should exist after resume" }
            }
            require(threadLocal.get() == null) { "4 - thread local should not exist outside the withContext" }
            call.respondText("Hello World!")
        }
    }
}

ktor-version = "2.3.13" & development = false

/
500: java.lang.IllegalArgumentException: 4 - transaction should not exist at the end

/foo
Hello World!

/bar
Hello World!

ktor-version = "2.3.13" & development = true

/
500: java.lang.IllegalArgumentException: 4 - transaction should not exist at the end

/foo
Hello World!

/bar
Hello World!

ktor-version = "3.2.0" & development = false

/
Hello World!

/foo
Hello World!

/bar
Hello World!

ktor-version = "3.2.0" & development = true

/
500: java.lang.IllegalArgumentException: 3 - transaction should exist after resume

/
500: java.lang.IllegalArgumentException: 1 - transaction should not exist at the start // 2nd call

/foo
500: java.lang.IllegalArgumentException: 3 - thread local should exist after resume

/bar
500: java.lang.IllegalArgumentException: 4 - thread local should not exist outside the withContext