monix.execution.cancelables.BooleanCancelable.scala Maven / Gradle / Ivy
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/*
* Copyright (c) 2014-2019 by The Monix Project Developers.
* See the project homepage at: https://monix.io
*
* 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 monix.execution.cancelables
import monix.execution.Cancelable
import monix.execution.Cancelable.Empty
import monix.execution.atomic.AtomicAny
/**
* Represents a Cancelable that can be queried for the canceled status.
*/
trait BooleanCancelable extends Cancelable {
/** @return true in case this cancelable hasn't been canceled,
* or false otherwise.
*/
def isCanceled: Boolean
}
object BooleanCancelable {
/** Builder for [[BooleanCancelable]]. */
def apply(): BooleanCancelable =
new BooleanCancelable {
@volatile private[this] var _isCanceled = false
def isCanceled = _isCanceled
def cancel(): Unit = {
if (!_isCanceled) _isCanceled = true
}
}
/** Builder for [[BooleanCancelable]].
*
* @param callback is a function that will execute exactly once
* on canceling.
*/
def apply(callback: () => Unit): BooleanCancelable =
new BooleanCancelableTask(callback)
/** Returns an instance of a [[BooleanCancelable]] that's
* already canceled.
*/
val alreadyCanceled: BooleanCancelable with Empty =
new BooleanCancelable with Empty {
val isCanceled = true
def cancel() = ()
}
/** Returns a [[BooleanCancelable]] that can never be canceled.
*
* Useful as a low-overhead instance whose `isCanceled` value
* is always `false`, thus similar in spirit with [[alreadyCanceled]].
*/
val dummy: BooleanCancelable =
new BooleanCancelable with Cancelable.IsDummy {
val isCanceled = false
def cancel() = ()
}
private final class BooleanCancelableTask(cb: () => Unit) extends BooleanCancelable {
private[this] val callbackRef = AtomicAny(cb)
def isCanceled: Boolean = callbackRef.get eq null
def cancel(): Unit = {
// Setting the callback to null with a `getAndSet` is solving
// two problems: `cancel` is thus idempotent, plus we allow
// the garbage collector to collect the task.
val callback = callbackRef.getAndSet(null)
if (callback != null) callback()
}
}
}