newSingleThreadContext on Native can't close until timeouts finish

[dkhalanskyjb]

Reported in the Kotlin Slack originally.

Simplified reproducer:

    @Test
    fun timeoutAffectsClosing() = runBlocking {
        val disp: CloseableCoroutineDispatcher = newSingleThreadContext("my-test")
        val result = withContext(disp) {
            // Disabling the inner timeout will make it work correctly
            withTimeout(30.seconds) {
                "Hello"
            }
        }
        println(result) // Print "Hello"
        disp.close()
        println("Dispatcher closed: $disp") // takes 30 seconds to get here
    }

[cmelchior]

A work-around seems to be to use newFixedThreadPool(1, "my-test") instead of newSingleThreadContext("my-test"). This is working on Coroutines 1.6.4 -> 1.7.1.

[cmelchior]

After some more testing, it seems that the above fix hits another bug. Trying to use the closed dispatcher doesn't throw an IllegalStateException but rather seems to hang for the timeout that was defined (in another part of the code).

This problematic behavior only occurs on Coroutines 1.6.4. On 1.7.0 and 1.71 an IllegalStateException is correctly thrown immediately.

    @Test
    fun timeoutAffectsClosing() = runBlocking {
        val disp: CloseableCoroutineDispatcher = newSingleThreadContext("my-test")
        val result = withContext(disp) {
            // Disabling the inner timeout will make it work correctly
            withTimeout(30.seconds) {
                "Hello"
            }
        }
        println(result)
        disp.close()

        // Attempt to use the dispatcher result in the same timeout behaviour (i.e. needing to
        // wait 30 seconds for `kotlin.IllegalStateException: Worker is already terminated`
        // This is only a problem on Coroutines 1.6.4, and seems to be fixed in 1.7.0.
        withContext(disp) {
            // Do nothing
        }
        println("Done")
    }