CoroutineScheduler: oversubscription in Dispatchers.Default when switching to IO with CPU tasks in local queue

[qwwdfsad]

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package kotlinx.coroutines.scheduling

import kotlinx.coroutines.*
import kotlinx.coroutines.scheduling.CoroutineScheduler.Companion.MAX_SUPPORTED_POOL_SIZE
import org.junit.*
import java.util.concurrent.*
import java.util.concurrent.atomic.AtomicInteger

class CoroutineSchedulerOversubscriptionStressTest : TestBase() {

    private val poolSize = Runtime.getRuntime().availableProcessors()
    private val inDefault = AtomicInteger(0)

    fun doCheck() {
        println("In default dispatcher, blocking thread #${inDefault.incrementAndGet()}, max allowed threads: $poolSize")
    }

    @Test
    fun testOverSubscription() = runTest {
        val barrier = CountDownLatch(1)

        // All threads but one
        repeat(CORE_POOL_SIZE - 1) {
            launch(Dispatchers.Default) {
                doCheck()
                barrier.await()
            }
        }
        Thread.sleep(200)
        withContext(Dispatchers.Default) {
            // Put a task in a local queue, it will be stolen
            launch(Dispatchers.Default) {
                doCheck()
                barrier.await()
            }
            // Put one more task to trick the local queue check
            launch(Dispatchers.Default) {
                doCheck()
                barrier.await()
            }

            withContext(Dispatchers.IO) {
                Thread.sleep(1000) // Wait for stealing
            }
        }
    }

}

Will print In default dispatcher, blocking thread #17, max allowed threads: 16