I want to simulate the following behaviour using c...

# coroutines

[czuckie]

I want to simulate the following behaviour using coroutines:

val executor = Executors.singleThreadExecutor()

fun oneAtATime(workToDo: Boop) {
   return executor.submit {
      doSomethingWIthThe(workToDo)
   }.get()
}

Where oneAtATime(...) may be invoked by multiple threads, but will only allow one operation at a time due to the single thread executor.

[czuckie]

is it as simple as creating a new coroutineScope with a single thread executor .asCoroutineDispatcher?

[Joffrey]

You could indeed use withContext() and pass a single thread dispatcher (no need for a coroutine scope, just a dispatcher). However, if what you want is mutual exclusion, you should probably just use a Mutex and protect the piece of code with mutex.withLock { ... }

[czuckie]

cheers Joffrey, I'll give it a go! 🤜 💥 🤛

[ephemient]

is that structure actually what you want? consider an alternative, if you have an appropriate owning scope,

private val workQueue = MutableSharedFlow<Boop>()
private val worker = scope.launch {
    workQueue.collect { workToDo ->
        doSomethingWithThe(workToDo)
    }
}
suspend fun oneAtATime(workToDo: Boop) {
    workQueue.emit(workToDo)
}

which makes it more obvious that the work is being processed sequentially and uniformly, without requiring additional locking

[Joffrey]

For some reason I was assuming a result was expected by oneAtATime() but you're right, in the OP there is no such result, which makes it possible to just enqueue asynchronously

[ephemient]

unless the function is expected to block or has a non-Unit return type which is missing in the example, in which case your proposal is better

[Dmitry Khalanskiy [JB]]

How about using limitedParallelism on a dispatcher of your choice? https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-coroutine-dispatcher/limited-parallelism.html

val dispatcher = Dispatchers.Default.limitedParallelism(1)

suspend fun oneAtATime(workToDo: Boop) = withContext(dispatcher) {
  doSomethingWIthThe(workToDo)
}

[czuckie]

oooo limited parallelism looks like a nice approach, that's super duper obvious! Thanks all

[ephemient]

whether limitedParallelism works depends on what your doSomethingWithThe() function does. if it requires parallelism internally, that's a problem, but if it's just a blocking call then you're fine

[uli]

Be aware though… Single threaded dispatchers and limited parallelism just limit … well … parallelism.
If doSomethingWIthThe(workToDo) is suspending, multiple coroutines could still be suspended and resumed concurrently.