Another possibility might be ``` val coroJob = AtomicReference<Job> () /// Start my cor...

# coroutines

[Niklas Gürtler]

Another possibility might be

val coroJob = AtomicReference<Job> ()
    /// Start my coroutine, may be called from any thread
    fun startCoro () {

        val coro = coroutineScope.launch(<http://Dispatchers.IO|Dispatchers.IO>, start = LAZY) {
            // Do the actual work here ...
            coroJob.set(null)
        }

        // If coroJob isn't null, do nothing.
        if (coroJob.compareAndSet(null, coro))
            coro.start()
    }

which avoids the explicit context switches and should still be thread-safe. Is there a more idiomatic and safe way to do that?

[uli]

What happens if you make coro a property and just start it multiple times?

[Niklas Gürtler]

Dunno, probably an exception 😉

[uli]

Dunno? But are you interested in finding out? You could check the kdoc. It might solve your problem?

[Niklas Gürtler]

Ah, it will simply return false and not do anything if that coro was already started or completed. So not very useful here.

[uli]

Isn't that what you want? Star a coro the first time startCoro is called and do nothing if it is already started?

[Niklas Gürtler]

but i want to re-start it if it was completed

[uli]

I see. Then I guess it does not get much simpler then what you have.

[uli]

Just watch out for a coroutine leak. In the code above, you are always launching a new coroutine, leaving it dangling in the NEW state.

[Niklas Gürtler]

It's not launched, just created (lazy)... Doesn't it get GC'd?

[uli]

No. It is launched lazy

[Niklas Gürtler]

But there isn't any reference to the Job, so it can't ever be launched, so the GC should collect it?

[uli]

I would expect it to stay around

[uli]

if you start it, there still is no ref and it would live until completed

[Niklas Gürtler]

maybe an else coro.cancel() would help

[uli]

How about this one?

val coroRunning = AtomicBoolean(false)

/// Start my coroutine, may be called from any thread
fun startCoro () {
    // If coro is running, do nothing.
    if (coroRunning.compareAndExchange(false, true)) {
        coroutineScope.launch(<http://Dispatchers.IO|Dispatchers.IO>) {
            // Do the actual work here ...
            coroRunning.set(false)
        }
    }
}

[Niklas Gürtler]

looks nice... Hmm, I think some requirements changed and I have to do the whole thing differently 🤦‍♂️ thanks anyways 😄

[uli]

🙂 - Good luck