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answer is: not exactly. It all works with the assumption that the underlying executor will throw if shutdown. I was looking at “bad” code that’s wrapping an android handler and not throwing if the task is rejected, hence blocking forever

You can do use `asCoroutineDispatcher()` on a `Handler` instance, it's part of kotlinx-coroutines-android, I think the implementation it provides is correct for this edge case.

And here's the canonical permalink on GitHub: <https://github.com/Kotlin/kotlinx.coroutines/blob/b852b20131fff5c0d605d7cb5f8001b715f02c1e/ui/kotlinx-coroutines-android/src/HandlerDispatcher.kt#L131|https://github.com/Kotlin/kotlinx.coroutines/blob/b852b20131fff5c0d605d7cb5f8001b715f02c1e/ui/kotlinx-coroutines-android/src/HandlerDispatcher.kt#L131>

Do you want to send the PR, or should I do it?

What’s the fix for `asCoroutineDispatcher`? I didn’t think the `dispatch` method was allowed to throw, so the execution rejected exception approach wouldn’t work?

Great question! Executor.asCoroutineDispatcher() catches rejection and delegates the work to <http://Dispatchers.IO|Dispatchers.IO> : <https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/jvm/src/Executors.kt#L92-L100>

<https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/java.util.concurrent.-executor/as-coroutine-dispatcher.html>

&gt;  If the underlying executor throws <http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/RejectedExecutionException.html|RejectedExecutionException> on attempt to submit a continuation task (it happens when <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-executor-coroutine-dispatcher/close.html|closing> the resulting dispatcher, on underlying executor <http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html#shutdown()|shutdown>, or when it uses limited queues), then the <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-job/index.html|Job> of the affected task is <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/java.util.concurrent.-executor/as-coroutine-dispatcher.html#|cancelled> and the task is submitted to the <http://Dispatchers.IO|Dispatchers.IO>, so that the affected coroutine can cleanup its resources and promptly complete.

&gt;  Do you want to send the PR, or should I do it?
<@U3ZLHBTLG> you’re welcome to. This might be quite involved (look at the Executors impl), maybe worth filing an issue?

<https://twitter.com/Piwai/status/1406301224295710720?s=19|https://twitter.com/Piwai/status/1406301224295710720?s=19>