How to produce a Traversable with cats-effect's IO given an async that will call multiple times - scala

Question

What I'm really trying to do is monitor multiple files and when any of them is modified I'd like to update some state and produce a side effect using this state. I imagine what I want is a scan over a Traversable that produces a Traversable[IO[_]]. But I don't see the path there.
as a minimal attempt to produce this I wrote
package example
import better.files.{File, FileMonitor}
import cats.implicits._
import com.monovore.decline._
import cats.effect.IO
import java.nio.file.{Files, Path}
import scala.concurrent.ExecutionContext.Implicits.global
object Hello extends CommandApp(
name = "cats-effects-playground",
header = "welcome",
main = {
val filesOpts = Opts.options[Path]("input", help = "input files")
filesOpts.map { files =>
IO.async[File] { cb =>
val watchers = files.map { path =>
new FileMonitor(path, recursive = false) {
override def onModify(file: File, count: Int) = cb(Right(file))
}
}
watchers.toList.foreach(_.start)
}
.flatMap(f => IO { println(f) })
.unsafeRunSync
}
}
)
but this has two major flaws. One it creates a thread for each file I'm watching, which is a little heavy. But more importantly the program finishes as soon as a single file is modified, even though onModify would be called more times if the program stayed running.
I'm not married to using better-files, it just seemed like the path of least resistance. But I do require using Cats IO.

Answer 1

This solution doesn't solve the issue of creating a bunch of threads, and it doesn't strictly produce a Traversable, but it solves the underlying use case. I'm very open to this being critiqued and a better solution provided.
package example
import better.files.{File, FileMonitor}
import cats.implicits._
import com.monovore.decline._
import cats.effect.IO
import java.nio.file.{Files, Path}
import java.util.concurrent.LinkedBlockingQueue
import scala.concurrent.ExecutionContext.Implicits.global
object Hello extends CommandApp(
name = "cats-effects-playground",
header = "welcome",
main = {
val filesOpts = Opts.options[Path]("input", help = "input files")
filesOpts.map { files =>
val bq: LinkedBlockingQueue[IO[File]] = new LinkedBlockingQueue()
val watchers = files.map { path =>
new FileMonitor(path, recursive = false) {
override def onModify(file: File, count: Int) = bq.put(IO(file))
}
}
def ioLoop(): IO[Unit] = bq.take()
.flatMap(f => IO(println(f)))
.flatMap(_ => ioLoop())
watchers.toList.foreach(_.start)
ioLoop.unsafeRunSync
}
}
)