Hi, we are facing some issue with CIO client engin...

# ktor

[Leon Kiefer]

Hi, we are facing some issue with CIO client engine (version 2.3.0) when doing concurrent requests:

Exception in thread "main" java.lang.IllegalStateException: The number of released permits cannot be greater than 100
	at kotlinx.coroutines.sync.SemaphoreImpl.release(Semaphore.kt:184)
	at io.ktor.client.engine.cio.ConnectionFactory.connect(ConnectionFactory.kt:32)
	at io.ktor.client.engine.cio.ConnectionFactory$connect$1.invokeSuspend(ConnectionFactory.kt)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:104)
	at kotlinx.coroutines.internal.LimitedDispatcher.run(LimitedDispatcher.kt:42)
	at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:95)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:570)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:677)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:664)

Looks like more permits are released then the maximum in this code here https://github.com/ktorio/ktor/blob/2.3.0/ktor-client/ktor-client-cio/jvmAndNix/src/io/ktor/client/engine/cio/ConnectionFactory.kt
This only happens while doing many PUT requests with huge bodies (batch) and long response times. There are also some io.ktor.client.network.sockets.ConnectTimeoutException and java.io.EOFException which we are retrying.
We have limited the concurrency of requests to 5 by using an additional Semaphore.

In a different part of the application we are doing GET requests with a concurrency of 100 and 1000 rps with the same ktor client without any problems.

[e5l]

Hey @Leon Kiefer, could you log an issue?

[Leon Kiefer]

in Github or YouTrack?

[e5l]

YouTrack would be great

[Leon Kiefer]

https://youtrack.jetbrains.com/issue/KTOR-5992

[spierce7]

In the mean time, why not move to Netty instead of CIO to see if that resolves your issue?