Concurrent - sleep & waitFor (#1449)

Author: nomisRev

modules/effects/arrow-effects-data/src/main/kotlin/arrow/effects/internal/ConcurrentSleep.kt

@@ -0,0 +1,50 @@
+package arrow.effects.internal
+
+import arrow.Kind
+import arrow.core.Either
+import arrow.core.Left
+import arrow.core.Right
+import arrow.effects.typeclasses.Concurrent
+import arrow.effects.typeclasses.Duration
+import java.util.concurrent.Executors
+import java.util.concurrent.ScheduledExecutorService
+import kotlin.coroutines.Continuation
+import kotlin.coroutines.CoroutineContext
+import kotlin.coroutines.startCoroutine
+
+@Suppress("FunctionName")
+internal fun <F> Concurrent<F>.ConcurrentSleep(duration: Duration): Kind<F, Unit> = cancelable { cb ->
+  val cancelRef = scheduler.schedule(ShiftTick(dispatchers().default(), cb), duration.amount, duration.timeUnit)
+  delay { cancelRef.cancel(false); Unit }
+}
+
+/**
+ * [scheduler] is **only** for internal use for the [Concurrent.sleep] implementation.
+ * This way we can guarantee nothing besides sleeping ever occurs here.
+ */
+internal val scheduler: ScheduledExecutorService by lazy {
+  Executors.newScheduledThreadPool(2) { r ->
+    Thread(r).apply {
+      name = "arrow-effect-scheduler-$id"
+      isDaemon = true
+    }
+  }
+}
+
+/**
+ * [ShiftTick] is a small utility to [Concurrent.shift] work away from the [ScheduledExecutorService].
+ * As mentioned in [scheduler] no work should ever happen there.
+ * So after sleeping we need to shift away to not keep that thread occupied.
+ */
+internal class ShiftTick(
+  private val ctx: CoroutineContext,
+  private val cb: (Either<Throwable, Unit>) -> Unit
+) : Runnable {
+  override fun run() {
+    suspend { Unit }.startCoroutine(Continuation(ctx) {
+      it.fold({ unit -> cb(Right(unit)) }, { e -> cb(Left(e)) })
+    })
+  }
+}
+
+class TimeoutException(override val message: String) : Exception()

modules/effects/arrow-effects-data/src/main/kotlin/arrow/effects/typeclasses/Concurrent.kt

@@ -13,6 +13,8 @@ import arrow.effects.CancelToken
 import arrow.effects.KindConnection
 import arrow.effects.MVar
 import arrow.effects.data.internal.BindingCancellationException
+import arrow.effects.internal.ConcurrentSleep
+import arrow.effects.internal.TimeoutException
 import arrow.typeclasses.MonadContinuation
 import java.util.concurrent.atomic.AtomicReference
 import kotlin.coroutines.CoroutineContext
@@ -722,6 +724,90 @@ interface Concurrent<F> : Async<F> {
 
   override fun <B> binding(c: suspend MonadContinuation<F, *>.() -> B): Kind<F, B> =
     bindingCancellable { c() }.a
+
+  /**
+   *  Sleeps for a given [duration] without blocking a thread.
+   *  Used to derive [waitFor] and can be used to created timed events like backing-off retries.
+   *
+   * ```kotlin:ank:playground
+   * import arrow.*
+   * import arrow.effects.*
+   * import arrow.effects.typeclasses.*
+   * import arrow.effects.extensions.io.concurrent.concurrent
+   *
+   * fun main(args: Array<String>) {
+   *   //sampleStart
+   *   fun <F> Concurrent<F>.delayHelloWorld(): Kind<F, Unit> =
+   *     sleep(3.seconds).flatMap {
+   *       delay { println("Hello World!") }
+   *     }
+   *   //sampleEnd
+   *   IO.concurrent().delayHelloWorld()
+   *     .fix().unsafeRunSync()
+   * }
+   * ```
+   * @see waitFor
+   **/
+  fun sleep(duration: Duration): Kind<F, Unit> = ConcurrentSleep(duration)
+
+  /**
+   * Returns the result of [this] within the specified [duration] or the [default] value.
+   *
+   * ```kotlin:ank:playground
+   * import arrow.*
+   * import arrow.effects.*
+   * import arrow.effects.typeclasses.*
+   * import arrow.effects.extensions.io.concurrent.concurrent
+   *
+   * fun main(args: Array<String>) {
+   *   //sampleStart
+   *   fun <F> Concurrent<F>.timedOutWorld(): Kind<F, Unit> {
+   *     val world = sleep(3.seconds).flatMap { delay { println("Hello World!") } }
+   *     val fallbackWorld = delay { println("Hello from the backup") }
+   *     return world.waitFor(1.seconds, fallbackWorld)
+   *   }
+   *   //sampleEnd
+   *   IO.concurrent().timedOutWorld()
+   *     .fix().unsafeRunSync()
+   * }
+   * ```
+   **/
+  fun <A> Kind<F, A>.waitFor(duration: Duration, default: Kind<F, A>): Kind<F, A> =
+    dispatchers().default().raceN(this, sleep(duration)).flatMap {
+      it.fold(
+        { a -> just(a) },
+        { default }
+      )
+    }
+
+  /**
+   * Returns the result of [this] within the specified [duration] or the raises a [TimeoutException] exception.
+   *
+   * ```kotlin:ank:playground
+   * import arrow.*
+   * import arrow.effects.*
+   * import arrow.effects.typeclasses.*
+   * import arrow.effects.extensions.io.concurrent.concurrent
+   *
+   * fun main(args: Array<String>) {
+   *   //sampleStart
+   *   fun <F> Concurrent<F>.timedOutWorld(): Kind<F, Unit> {
+   *     val world = sleep(1.seconds).flatMap { delay { println("Hello World!") } }
+   *     return world.waitFor(3.seconds)
+   *   }
+   *   //sampleEnd
+   *   IO.concurrent().timedOutWorld()
+   *     .fix().unsafeRunSync()
+   * }
+   * ```
+   **/
+  fun <A> Kind<F, A>.waitFor(duration: Duration): Kind<F, A> =
+    dispatchers().default().raceN(this, sleep(duration)).flatMap {
+      it.fold(
+        { a -> just(a) },
+        { raiseError(TimeoutException(duration.toString())) }
+      )
+    }
 }
 
 /** Alias for `Either` structure to provide consistent signature for race methods. */