How to read all available elements from a Channel in Kotlin - kotlin

Question

I would like to read all available elements from a channel so that I can do batch processing on them if my receiver is slower then my sender (in hopes that processing a batch will be more performant and allow the receiver to catch up). I only want to suspend if the channel is empty, not suspend until my batch is full or timeout unlike this question.
Is there anything built into the standard kotlin library to accomplish this?

Answer 1

I did not find anything in the standard kotlin library, but here is what I came up with. This will suspend only for the first element and then poll all remaining elements. This only really works with a Buffered Channel so that elements ready for processing are queued and available for poll
/**
* Receive all available elements up to [max]. Suspends for the first element if the channel is empty
*/
internal suspend fun <E> ReceiveChannel<E>.receiveAvailable(max: Int): List<E> {
if (max <= 0) {
return emptyList()
}
val batch = mutableListOf<E>()
if (this.isEmpty) {
// suspend until the next message is ready
batch.add(receive())
}
fun pollUntilMax() = if (batch.size >= max) null else poll()
// consume all other messages that are ready
var next = pollUntilMax()
while (next != null) {
batch.add(next)
next = pollUntilMax()
}
return batch
}

Answer 2

I tested Jakes code and it worked well for me (thanks!). Without max limit, I got it down to:
suspend fun <E> ReceiveChannel<E>.receiveAvailable(): List<E> {
val allMessages = mutableListOf<E>()
allMessages.add(receive())
var next = poll()
while (next != null) {
allMessages.add(next)
next = poll()
}
return allMessages
}