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com.velocidi.apso.caching.LruCache.scala Maven / Gradle / Ivy
/*
* Copyright © 2011-2015 the spray project
*
* 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 com.velocidi.apso.caching
import com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap
import scala.annotation.tailrec
import scala.collection.JavaConverters._
import scala.concurrent.duration.Duration
import scala.concurrent.{ ExecutionContext, Future, Promise }
import scala.util.{ Failure, Success }
object LruCache {
//# source-quote-LruCache-apply
/**
* Creates a new [[ExpiringLruCache]] or
* [[SimpleLruCache]] instance depending on whether
* a non-zero and finite timeToLive and/or timeToIdle is set or not.
*/
def apply[V](
maxCapacity: Int = 500,
initialCapacity: Int = 16,
timeToLive: Duration = Duration.Inf,
timeToIdle: Duration = Duration.Inf): Cache[V] = {
//#
def check(dur: Duration, name: String) =
require(
dur != Duration.Zero,
s"Behavior of LruCache.apply changed: Duration.Zero not allowed any more for $name parameter. To disable " +
"expiration use Duration.Inf instead of Duration.Zero")
// migration help
check(timeToLive, "timeToLive")
check(timeToIdle, "timeToIdle")
if (timeToLive.isFinite || timeToIdle.isFinite)
new ExpiringLruCache[V](maxCapacity, initialCapacity, timeToLive, timeToIdle)
else
new SimpleLruCache[V](maxCapacity, initialCapacity)
}
}
/**
* A thread-safe implementation of [[Cache]].
* The cache has a defined maximum number of entries it can store. After the maximum capacity is reached new
* entries cause old ones to be evicted in a last-recently-used manner, i.e. the entries that haven't been accessed for
* the longest time are evicted first.
*/
final class SimpleLruCache[V](val maxCapacity: Int, val initialCapacity: Int) extends Cache[V] {
require(maxCapacity >= 0, "maxCapacity must not be negative")
require(initialCapacity <= maxCapacity, "initialCapacity must be <= maxCapacity")
private[caching] val store = new ConcurrentLinkedHashMap.Builder[Any, Future[V]]
.initialCapacity(initialCapacity)
.maximumWeightedCapacity(maxCapacity)
.build()
def get(key: Any) = Option(store.get(key))
def apply(key: Any, genValue: () => Future[V])(implicit ec: ExecutionContext): Future[V] = {
val promise = Promise[V]()
store.putIfAbsent(key, promise.future) match {
case null =>
val future = genValue()
future.onComplete { value =>
promise.complete(value)
// in case of exceptions we remove the cache entry (i.e. try again later)
if (value.isFailure) store.remove(key, promise.future)
}
future
case existingFuture => existingFuture
}
}
def remove(key: Any) = Option(store.remove(key))
def clear(): Unit = { store.clear() }
def keys: Set[Any] = store.keySet().asScala.toSet
def ascendingKeys(limit: Option[Int] = None) =
limit.map { lim => store.ascendingKeySetWithLimit(lim) }
.getOrElse(store.ascendingKeySet())
.iterator().asScala
def size = store.size
}
/**
* A thread-safe implementation of [[Cache]].
* The cache has a defined maximum number of entries is can store. After the maximum capacity has been reached new
* entries cause old ones to be evicted in a last-recently-used manner, i.e. the entries that haven't been accessed for
* the longest time are evicted first.
* In addition this implementation optionally supports time-to-live as well as time-to-idle expiration.
* The former provides an upper limit to the time period an entry is allowed to remain in the cache while the latter
* limits the maximum time an entry is kept without having been accessed. If both values are non-zero the time-to-live
* has to be strictly greater than the time-to-idle.
* Note that expired entries are only evicted upon next access (or by being thrown out by the capacity constraint), so
* they might prevent gargabe collection of their values for longer than expected.
*
* @param timeToLive the time-to-live in millis, zero for disabling ttl-expiration
* @param timeToIdle the time-to-idle in millis, zero for disabling tti-expiration
*/
final class ExpiringLruCache[V](maxCapacity: Long, initialCapacity: Int,
timeToLive: Duration, timeToIdle: Duration) extends Cache[V] {
require(
!timeToLive.isFinite || !timeToIdle.isFinite || timeToLive > timeToIdle,
s"timeToLive($timeToLive) must be greater than timeToIdle($timeToIdle)")
private[caching] val store = new ConcurrentLinkedHashMap.Builder[Any, Entry[V]]
.initialCapacity(initialCapacity)
.maximumWeightedCapacity(maxCapacity)
.build()
@tailrec
def get(key: Any): Option[Future[V]] = store.get(key) match {
case null => None
case entry if (isAlive(entry)) =>
entry.refresh()
Some(entry.future)
case entry =>
// remove entry, but only if it hasn't been removed and reinserted in the meantime
if (store.remove(key, entry)) None // successfully removed
else get(key) // nope, try again
}
def apply(key: Any, genValue: () => Future[V])(implicit ec: ExecutionContext): Future[V] = {
def insert() = {
val newEntry = new Entry(Promise[V]())
val valueFuture =
store.put(key, newEntry) match {
case null => genValue()
case entry =>
if (isAlive(entry)) {
// we date back the new entry we just inserted
// in the meantime someone might have already seen the too fresh timestamp we just put in,
// but since the original entry is also still alive this doesn't matter
newEntry.created = entry.created
entry.future
} else genValue()
}
valueFuture.onComplete { value =>
newEntry.promise.tryComplete(value)
// in case of exceptions we remove the cache entry (i.e. try again later)
if (value.isFailure) store.remove(key, newEntry)
}
newEntry.promise.future
}
store.get(key) match {
case null => insert()
case entry if (isAlive(entry)) =>
entry.refresh()
entry.future
case _ => insert()
}
}
def remove(key: Any) = store.remove(key) match {
case null => None
case entry if (isAlive(entry)) => Some(entry.future)
case _ => None
}
def clear(): Unit = { store.clear() }
def keys: Set[Any] = store.keySet().asScala.toSet
def ascendingKeys(limit: Option[Int] = None) =
limit.map { lim => store.ascendingKeySetWithLimit(lim) }
.getOrElse(store.ascendingKeySet())
.iterator().asScala
def size = store.size
private def isAlive(entry: Entry[V]) =
(entry.created + timeToLive).isFuture &&
(entry.lastAccessed + timeToIdle).isFuture
}
private[caching] class Entry[T](val promise: Promise[T]) {
@volatile var created = Timestamp.now
@volatile var lastAccessed = Timestamp.now
def future = promise.future
def refresh(): Unit = {
// we dont care whether we overwrite a potentially newer value
lastAccessed = Timestamp.now
}
override def toString = future.value match {
case Some(Success(value)) => value.toString
case Some(Failure(exception)) => exception.toString
case None => "pending"
}
}
