Memory leak in coroutines 1.4.x

[sunpeaksfivemile]

I've encountered a memory leak which I believe is caused by a race condition in the coroutine library.

I've simplified the leak down to the following repro code:

private suspend fun <T : Any> ReceiveChannel<T>.receiveBatch(size: Int): List<T> {
    return List(size) { receive() }
}

fun main() = runBlocking {
    class Thing(val counter: Long /* for debugging on the heap dump */)

    val channel1 = produce(capacity = 64) { // from the main thread
        (0 until Long.MAX_VALUE).forEach {
            send(Thing(it))
        }
    }

    launch(newSingleThreadContext("Channel2")) { // to a single thread (This thread is important! no leak if everything is single threaded)
        flow {
            while (true) {
                emit(channel1.receiveBatch(64))
            }
        }.collect { }
    }

    Unit
}

This sample code leaks Things very rapidly

I haven't dug too deep, but one interesting thing is if I inline the code for receive batch, there is no leak. Example:

fun main() = runBlocking {
    class Thing(val counter: Long /* for debugging on the heap dump */)

    val channel1 = produce(capacity = 64) { // from the main thread
        (0 until Long.MAX_VALUE).forEach {
            send(Thing(it))
        }
    }

    launch(newSingleThreadContext("Channel2")) { // to a single thread (This thread is important! no leak if everything is single threaded)
        flow {
            while (true) {
                emit(List(64) { channel1.receive() })
            }
        }.collect { }
    }

    Unit
}

Tested with kotlin 1.4.30 and coroutines-core 1.4.3

[IRus]

Able to reproduce

[qwwdfsad]

Great job with a simple reproducer! Investigating this

[shmuelr]

Hey, it seems this is marked as fixed in #2581 along with a corresponding test https://github.com/Kotlin/kotlinx.coroutines/pull/2581/files#diff-ed434c42575944931c44e85218440a92177bd346ad6791cf22c45820c75413e7

Is this still an issue?
Thanks!

[qwwdfsad]

It will be fixed in an upcoming release. Version 1.4.3 still has this issue