I have a `Thread` that's already running (for legacy reasons, it needs to be a `Thread` for now). In...

# coroutines

[Youssef Shoaib [MOD]]

I have a Thread that's already running (for legacy reasons, it needs to be a Thread for now). Inside a suspend function, how can I call thread.join() in a "better" manner? As in, so that the coroutine suspends until the thread finishes.

[CLOVIS]

withContext(<http://Dispatchers.IO|Dispatchers.IO>) { 
    thread.join() 
}

[mkrussel]

There wouldn't be anything built in that is not blocking.

Best option would be to add something at the end of the work the thread is doing that would notify listeners when it is done. You can then suspend and wait for the notification. This relies on you having some control over the thread and the work it is doing.

[Youssef Shoaib [MOD]]

Looking at `Thread.join`'s code, it seems to just wait until thread.isAlive is false, so wouldn't I be able to use that as a condition to wait for? I do have control over the thread code, but I'm trying to not be too invasive

[Youssef Shoaib [MOD]]

I came up with this, but I don't know if its better or not:

coroutineScope { launch { while (thread.isAlive) delay(10) } }

[simon.vergauwen]

runInterruptible is probably a better choice than withContext.

A non-blocking option would be to somehow pass a CompletableDeferred as the task running in the Thread and await that.

I would personally prefer join in favor of looping, you can potentially also use newSingleThreadContext instead of <http://Dispatchers.IO|Dispatchers.IO> but be sure to close it.

[CLOVIS]

Oh, indeed runInterruptible(<http://Dispatchers.IO|Dispatchers.IO>) looks more appropriate. It's still blocking a thread.

[Youssef Shoaib [MOD]]

Thanks Ivan and Simon. I ended up using a CompletableDeferred and completing it at the end of the thread's code, then awaiting it instead of calling join

[CLOVIS]

That's even better 👍

[simon.vergauwen]

That would indeed the best option if possible, be sure to add it in a try { } finally { } block so it gets called regardless of exceptions 😉

[Youssef Shoaib [MOD]]

@simon.vergauwen Ooops yes I forgot! Good catch

[CLOVIS]

Pun intended? 🤔