Hello :wave: Playing around with `Channel` based p...

# coroutines

[Dariusz Kuc]

Hello 👋 Playing around with Channel based pipelines and was wondering whether you have any suggestions to make it better.
NOTE: for this exercise want to stick to channels only

Consider following basic example - fetch list of items and for each one of them fetch additional information (details + reviews) that will be used to final result

val result = mutableListOf()

val summaries = retrieveSummaries()
for (summary in summaries) {
   val details = retrieveDetails(summary.id)
   val reviews = retrieveReviews(summary.id)

   result.add(buildResult(summary, details, reviews)
}

return result

I could easily parallelize the above by doing something like

summaries.map { summary -> 
  async {
    val details = async { retrieveDetails(summary.id) }
    val reviews = async { retrieveReviews(summary.id) }
    
    buildResult(summary, details.await(), reviews.await())
  }
}

Currently trying to figure out what would be the "best" way to achieve the same using Channel . "Simplest" would be to do a sequence of channels

val summaries: ReceiveChannel<Summary> = summariesChannel()
val detailsAndSummaries: ReceiveChannel<Pair<Summary, Detail>> = detailsAndSummariesChannel(summaries)
val result: ReceiveChannel<Result> = resultChannel(detailsAndSummaries)

Looks like BroadcastChannel is marked obsolete but I guess logically it would make sense to broadcast summaries and then send both details and reviews from separate channels but I am unsure how to read from multiple channels at once (i.e. buildResult would need results from 3 channels). Any ideas/suggestions?

[Dominaezzz]

You can read from multiple channels using select and channel.onReceive .

[Dariusz Kuc]

looks like select is able to pick first available element from X channels -> my use case in the above is that I need to consume messages from 3 channels to create a single result type

[Dariusz Kuc]

i.e. something like RX zip operator (which is marked as deprecated on channels)

[jimn]

why stick to channels specifically? shared flows in latest deprecate broadcast channels

[jimn]

message has been deleted

[Dariusz Kuc]

Its an exercise - got another one using flows as well