I’m hitting a weird issue with nested `withTimeout...

# coroutines

[chrmelchior]

I’m hitting a weird issue with nested withTimeout , it seems to prevent closing the dispatcher being used. Anyone have any ideas why it might not work? (The code is a simplified example of the real code)

@Test
    fun nestedTimeouts() = runBlocking {
        val disp: CloseableCoroutineDispatcher = newSingleThreadContext("my-test")
        val result = withTimeout(30.seconds) {
            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") // We never reach here if the inner timeout is enabled
    }

It only deadlocks on Darwin, JVM platforms work fine 🤔

[Dmitry Khalanskiy [JB]]

Does it work if you remove the outer timeout?

[chrmelchior]

No, that also deadlocks

[chrmelchior]

This is on Kotlin 1.8.20 with Coroutines 1.6.4

[Dmitry Khalanskiy [JB]]

Could you try with coroutines 1.7.1? We reworked newSingleThreadContext quite a bit in 1.7.0, so maybe the issue is fixed already.

[Dmitry Khalanskiy [JB]]

Nevermind, I checked it, and the issue is still there. Thanks for the report!

[Dmitry Khalanskiy [JB]]

https://github.com/Kotlin/kotlinx.coroutines/issues/3768

[Dmitry Khalanskiy [JB]]

Workaround: use newFixedThreadPool(1, "my-test") instead.

[chrmelchior]

Uhhh, that works. Thanks… but I’m a bit surprised since newSingleThreadContext just seems to delegate to that?

public actual fun newSingleThreadContext(name: String): ExecutorCoroutineDispatcher =
    newFixedThreadPoolContext(1, name)

[Dmitry Khalanskiy [JB]]

That's the JVM implementation, on Native it's different: https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/native/src/MultithreadedDispatchers.kt#L14

[chrmelchior]

Ah, I might have gone to the wrong implementation 🙈

[chrmelchior]

Thanks a lot for the quick help 🙏