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Fiber.scala
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Fiber.scala
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/*
* Copyright (c) 2017-2018 The Typelevel Cats-effect Project Developers
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cats.effect
/**
* `Fiber` represents the (pure) result of an [[Async]] data type (e.g. [[IO]])
* being started concurrently and that can be either joined or cancelled.
*
* You can think of fibers as being lightweight threads, a fiber being a
* concurrency primitive for doing cooperative multi-tasking.
*
* For example a `Fiber` value is the result of evaluating [[IO.start]]:
*
* {{{
* val io = IO.shift *> IO(println("Hello!"))
*
* val fiber: IO[Fiber[IO, Unit]] = io.start
* }}}
*
* Usage example:
*
* {{{
* for {
* fiber <- IO.shift *> launchMissiles.start
* _ <- runToBunker.handleErrorWith { error =>
* // Retreat failed, cancel launch (maybe we should
* // have retreated to our bunker before the launch?)
* fiber.cancel *> IO.raiseError(error)
* }
* aftermath <- fiber.join
* } yield {
* aftermath
* }
* }}}
*/
trait Fiber[F[_], A] {
/**
* Triggers the cancellation of the fiber.
*
* Returns a new task that will complete when the cancellation is
* sent (but not when it is observed or acted upon).
*
* Note that if the background process that's evaluating the result
* of the underlying fiber is already complete, then there's nothing
* to cancel.
*/
def cancel: F[Unit]
/**
* Returns a new task that will await for the completion of the
* underlying fiber, (asynchronously) blocking the current run-loop
* until that result is available.
*/
def join: F[A]
}
object Fiber {
/**
* Given a `join` and `cancel` tuple, builds a [[Fiber]] value.
*/
def apply[F[_], A](join: F[A], cancel: F[Unit]): Fiber[F, A] =
Tuple(join, cancel)
private final case class Tuple[F[_], A](join: F[A], cancel: F[Unit])
extends Fiber[F, A]
}