Legacy Context Shfit Example

ex.scala

trait Statsd[F[_]] {
  def inc(key: String, magnitude: Int                          = 1, sampleRate: Double = 1.0): F[Unit]
  def dec(key: String, magnitude: Int                          = 1, sampleRate: Double = 1.0): F[Unit]
  def gauge(key: String, magnitude: Double, sampleRate: Double = 1.0): F[Unit]
  def timer(key: String, value: Int, sampleRate: Double        = 1.0): F[Unit]
}

// the legacy client takes in a fixed thread pool of 1.  Under the hood it does some
//    websocket / NIO stuff
//  am I wrong to contextShift onto the same thread pool that it's using?
//  in this example, ec here is the same as the ec that client() is using to make NIO calls 
//  or should I have ec2 (another fixed thread pool of 1) JUST for IO to be shifting onto when making calls 
// to client?

class UdpCatsStatds[F[_]: ContextShift : Sync](private val client: UdpStatsdClient, private val ec: ExecutionContext)
    extends Statsd[F] {
  def inc(key: String, magnitude: Int = 1, sampleRate: Double = 1.0): F[Unit] =
    ContextShift[F].evalOn(ec)(Sync[F].delay(client.inc(key, magnitude, sampleRate)))
  def dec(key: String, magnitude: Int, sampleRate: Double): F[Unit] =
    ContextShift[F].evalOn(ec)(Sync[F].delay(client.dec(key, magnitude, sampleRate)))
  def gauge(key: String, magnitude: Double, sampleRate: Double): F[Unit] =
    ContextShift[F].evalOn(ec)(Sync[F].delay(client.gauge(key, magnitude, sampleRate)))
  def timer(key: String, value: Int, sampleRate: Double): F[Unit] =
    ContextShift[F].evalOn(ec)(Sync[F].delay(client.timer(key, value, sampleRate)))
}

object UdpCatsStatsd {
  def make[F[_]: Sync: ContextShift](config: Config): Resource[F, UdpCatsStatds[F]] =
    Resource(Sync[F].delay {
      val executor = Executors.newFixedThreadPool(1)
      val ec = ExecutionContext.fromExecutor(executor)
      val underlyingClient = new UdpStatsdClient(config, Some(ec))
      val wrappedClient = new UdpCatsStatds[F](underlyingClient, ec)
      (wrappedClient, Sync[F].delay(executor.shutdown()))
    })
}