monix.execution.cancelables.MultiAssignCancelable.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.IsDummy
import monix.execution.atomic.{AtomicAny, PaddingStrategy}
import scala.annotation.tailrec
/** Represents a [[monix.execution.Cancelable Cancelable]] whose
* underlying cancelable reference can be swapped for another.
*
* Example:
* {{{
* val s = MultiAssignmentCancelable()
* s := c1 // sets the underlying cancelable to c1
* s := c2 // swaps the underlying cancelable to c2
*
* s.cancel() // also cancels c2
*
* s := c3 // also cancels c3, because s is already canceled
* }}}
*
* Also see:
*
* - [[SerialCancelable]], which is similar, except that it
* cancels the old cancelable upon assigning a new cancelable
* - [[SingleAssignCancelable]] that is effectively a forward
* reference that can be assigned at most once
* - [[OrderedCancelable]] that's very similar with
* `MultiAssignCancelable`, but with the capability of forcing
* ordering on concurrent updates
*/
final class MultiAssignCancelable private (initial: Cancelable) extends AssignableCancelable.Multi {
private[this] val state = {
AtomicAny.withPadding(initial, PaddingStrategy.LeftRight128)
}
override def isCanceled: Boolean =
state.get match {
case null => true
case _ => false
}
override def cancel(): Unit = {
// Using getAndSet, which on Java 8 should be faster than
// a compare-and-set.
val oldState: Cancelable = state.getAndSet(null)
if (oldState ne null) oldState.cancel()
}
@tailrec def `:=`(value: Cancelable): this.type =
state.get match {
case null =>
value.cancel()
this
case `value` =>
// ignore
this
case current =>
if (state.compareAndSet(current, value)) {
this
} else {
// $COVERAGE-OFF$
:=(value) // retry
// $COVERAGE-ON$
}
}
/** Clears the underlying reference, setting it to a
* [[Cancelable.empty]] (if not cancelled).
*
* This is equivalent with:
* {{{
* ref := Cancelable.empty
* }}}
*
* The purpose of this method is to release any underlying
* reference for GC purposes, however if the underlying reference
* is a [[monix.execution.Cancelable.IsDummy dummy]] then the
* assignment doesn't happen because we don't care about releasing
* dummy references.
*/
@tailrec def clear(): Cancelable = {
val current: Cancelable = state.get
if ((current ne null) && !current.isInstanceOf[IsDummy]) {
if (state.compareAndSet(current, Cancelable.empty)) {
current
} else {
// $COVERAGE-OFF$
clear() // retry
// $COVERAGE-ON$
}
} else {
Cancelable.empty
}
}
}
object MultiAssignCancelable {
/** Builder for [[MultiAssignCancelable]]. */
def apply(): MultiAssignCancelable =
new MultiAssignCancelable(Cancelable.empty)
/** Builder for [[MultiAssignCancelable]]. */
def apply(s: Cancelable): MultiAssignCancelable =
new MultiAssignCancelable(s)
}