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/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala
package collection.concurrent
import scala.annotation.tailrec
/** A template trait for mutable maps that allow concurrent access.
*
* $concurrentmapinfo
*
* @see [[http://docs.scala-lang.org/overviews/collections/concrete-mutable-collection-classes.html#concurrent_maps "Scala's Collection Library overview"]]
* section on `Concurrent Maps` for more information.
*
* @tparam K the key type of the map
* @tparam V the value type of the map
*
* @define Coll `concurrent.Map`
* @define coll concurrent map
* @define concurrentmapinfo
* This is a base trait for all Scala concurrent map implementations. It
* provides all of the methods a `Map` does, with the difference that all the
* changes are atomic. It also describes methods specific to concurrent maps.
*
* '''Note''': The concurrent maps do not accept `'''null'''` for keys or values.
*
* @define atomicop
* This is an atomic operation.
*/
trait Map[K, V] extends scala.collection.mutable.Map[K, V] {
/**
* Associates the given key with a given value, unless the key was already
* associated with some other value.
*
* $atomicop
*
* @param k key with which the specified value is to be associated with
* @param v value to be associated with the specified key
* @return `Some(oldvalue)` if there was a value `oldvalue` previously
* associated with the specified key, or `None` if there was no
* mapping for the specified key
*/
def putIfAbsent(k: K, v: V): Option[V]
/**
* Removes the entry for the specified key if it's currently mapped to the
* specified value.
*
* $atomicop
*
* @param k key for which the entry should be removed
* @param v value expected to be associated with the specified key if
* the removal is to take place
* @return `true` if the removal took place, `false` otherwise
*/
def remove(k: K, v: V): Boolean
/**
* Replaces the entry for the given key only if it was previously mapped to
* a given value.
*
* $atomicop
*
* @param k key for which the entry should be replaced
* @param oldvalue value expected to be associated with the specified key
* if replacing is to happen
* @param newvalue value to be associated with the specified key
* @return `true` if the entry was replaced, `false` otherwise
*/
def replace(k: K, oldvalue: V, newvalue: V): Boolean
/**
* Replaces the entry for the given key only if it was previously mapped
* to some value.
*
* $atomicop
*
* @param k key for which the entry should be replaced
* @param v value to be associated with the specified key
* @return `Some(v)` if the given key was previously mapped to some value `v`, or `None` otherwise
*/
def replace(k: K, v: V): Option[V]
override def getOrElseUpdate(key: K, op: => V): V = get(key) match {
case Some(v) => v
case None =>
val v = op
putIfAbsent(key, v) match {
case Some(nv) => nv
case None => v
}
}
/**
* Update a mapping for the specified key and its current optionally-mapped value
* (`Some` if there is current mapping, `None` if not).
*
* If the remapping function returns `Some(v)`, the mapping is updated with the new value `v`.
* If the remapping function returns `None`, the mapping is removed (or remains absent if initially absent).
* If the function itself throws an exception, the exception is rethrown, and the current mapping is left unchanged.
*
* If the map is updated by another concurrent access, the remapping function will be retried until successfully updated.
*
* @param key the key value
* @param remappingFunction a partial function that receives current optionally-mapped value and return a new mapping
* @return the new value associated with the specified key
*/
override def updateWith(key: K)(remappingFunction: Option[V] => Option[V]): Option[V] = updateWithAux(key)(remappingFunction)
@tailrec
private def updateWithAux(key: K)(remappingFunction: Option[V] => Option[V]): Option[V] = {
val previousValue = this.get(key)
val nextValue = remappingFunction(previousValue)
(previousValue, nextValue) match {
case (None, None) => None
case (None, Some(next)) if this.putIfAbsent(key, next).isEmpty => nextValue
case (Some(prev), None) if this.remove(key, prev) => None
case (Some(prev), Some(next)) if this.replace(key, prev, next) => nextValue
case _ => this.updateWithAux(key)(remappingFunction)
}
}
}
