Today I needed this ```class SuspendAtomicRef lt T Any gt private var data T = null private val mutex = Mutex suspend fun getOrSet init suspend gt T T return mutex withLock data init also data = it ``` Seems pretty basic so I wonder if I am missing it in the coroutines library

class SuspendAtomicRef<T : Any> {
    private var data: T? = null
    private val mutex = Mutex()

    suspend fun getOrSet(init: suspend () -> T): T {
        return mutex.withLock {
            data ?: init().also { data = it }
        }
    }
}

Seems pretty basic so I wonder if I am missing it in the coroutines library?

Dominaezzz

04/15/2021, 7:44 AM

Odd, why not just use an atomic ref? Would be faster.

spand

04/15/2021, 7:51 AM

It for an optimization so reducing multiple

init

invocations the entire point of it

Dominaezzz

04/15/2021, 7:53 AM

Ah, I missed the init part.

Given you still hit the mutex even after initialisation, there's still much room for improvement.

I also feel like I would refactor my code to not need this but that's probably just ignorance due to lack of use case.

ephemient

04/15/2021, 1:13 PM

https://github.com/Kotlin/kotlinx.coroutines/issues/706

spand

04/16/2021, 5:01 AM

Thanks for the hint @ephemient. I was actually using Louis suspendLazy previously but it sucks for properties. I think my

SuspendAtomicRef

work better in that: 1. Needs no coroutine on allocation (great for properties) 2. Supports cancellation much better in that a cancelled

init

will not break or block the others waiting.

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