Created
January 27, 2019 16:07
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Interruptible Streams using fs2 and cats-effect
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import scala.util.Random | |
import scala.concurrent.duration._ | |
import cats.effect.{ExitCode, IO, IOApp} | |
import cats.implicits._ | |
import fs2.Stream | |
import scala.concurrent.ExecutionContext.Implicits.global | |
import java.time.{Clock, ZoneOffset} | |
import fs2.concurrent.SignallingRef | |
object InterruptipleQueue extends IOApp { | |
override def run(args: List[String]): IO[ExitCode] = { | |
val clock = Clock.systemUTC() | |
def interrupter(signallingRef: SignallingRef[IO, Boolean]): Stream[IO, Unit] = { | |
for { | |
_ <- Stream.fixedDelay(1.seconds) // check every 1 second | |
_ <- Stream.eval { | |
val t = clock.instant().atOffset(ZoneOffset.UTC) | |
val on = t.getSecond <= 30 // the on/off logic (e.g. a light switch) | |
signallingRef.access flatMap { | |
case (current, set) => | |
// need update? | |
if (on != current) { | |
if (on) println(s"Seconds of $t <= 30: turning OFF.") | |
else println(s"Seconds of $t > 30: turning ON.") | |
set(on) | |
} else IO.unit | |
} | |
} | |
} yield () | |
} | |
def printer(signallingRef: SignallingRef[IO, Boolean]): Stream[IO, Int] = { | |
Stream | |
.iterateEval(0)(i => IO(i + 1)) | |
.metered(100 millis) | |
.pauseWhen(signallingRef) | |
} | |
(for { | |
signal <- Stream.eval(SignallingRef[IO, Boolean](false)) | |
ints <- printer(signal).concurrently(interrupter(signal)) | |
} yield ints) | |
.evalMap(i => IO(println(s"Got $i"))) | |
.compile | |
.drain | |
.as(ExitCode.Success) | |
} | |
} |
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