/
VersionVector.scala
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/
VersionVector.scala
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/*
* Copyright (C) 2009-2023 Lightbend Inc. <https://www.lightbend.com>
*/
package akka.cluster.ddata
import java.util.concurrent.atomic.AtomicLong
import scala.annotation.tailrec
import scala.collection.immutable.TreeMap
import akka.annotation.InternalApi
import akka.cluster.UniqueAddress
/**
* VersionVector module with helper classes and methods.
*/
object VersionVector {
private val emptyVersions: TreeMap[UniqueAddress, Long] = TreeMap.empty
val empty: VersionVector = ManyVersionVector(emptyVersions)
def apply(): VersionVector = empty
def apply(versions: TreeMap[UniqueAddress, Long]): VersionVector =
if (versions.isEmpty) empty
else if (versions.size == 1) apply(versions.head._1, versions.head._2)
else ManyVersionVector(versions)
def apply(node: UniqueAddress, version: Long): VersionVector = OneVersionVector(node, version)
/** INTERNAL API */
@InternalApi private[akka] def apply(versions: List[(UniqueAddress, Long)]): VersionVector =
if (versions.isEmpty) empty
else if (versions.tail.isEmpty) apply(versions.head._1, versions.head._2)
else apply(emptyVersions ++ versions)
/**
* Java API
*/
def create(): VersionVector = empty
sealed trait Ordering
case object After extends Ordering
case object Before extends Ordering
case object Same extends Ordering
case object Concurrent extends Ordering
/**
* Marker to ensure that we do a full order comparison instead of bailing out early.
*/
private case object FullOrder extends Ordering
/**
* Java API: The `VersionVector.After` instance
*/
def AfterInstance = After
/**
* Java API: The `VersionVector.Before` instance
*/
def BeforeInstance = Before
/**
* Java API: The `VersionVector.Same` instance
*/
def SameInstance = Same
/**
* Java API: The `VersionVector.Concurrent` instance
*/
def ConcurrentInstance = Concurrent
/** INTERNAL API */
@InternalApi private[akka] object Timestamp {
final val Zero = 0L
final val EndMarker = Long.MinValue
val counter = new AtomicLong(1L)
}
/**
* Marker to signal that we have reached the end of a version vector.
*/
private val cmpEndMarker = (null, Timestamp.EndMarker)
}
/**
* Representation of a Vector-based clock (counting clock), inspired by Lamport logical clocks.
* {{{
* Reference:
* 1) Leslie Lamport (1978). "Time, clocks, and the ordering of events in a distributed system". Communications of the ACM 21 (7): 558-565.
* 2) Friedemann Mattern (1988). "Virtual Time and Global States of Distributed Systems". Workshop on Parallel and Distributed Algorithms: pp. 215-226
* }}}
*
* Based on code from `akka.cluster.VectorClock`.
*
* This class is immutable, i.e. "modifying" methods return a new instance.
*/
@SerialVersionUID(1L)
sealed abstract class VersionVector extends ReplicatedData with ReplicatedDataSerialization with RemovedNodePruning {
type T = VersionVector
import VersionVector._
/**
* Increment the version for the node passed as argument. Returns a new VersionVector.
*/
def :+(node: SelfUniqueAddress): VersionVector = increment(node)
/**
* INTERNAL API
* Increment the version for the node passed as argument. Returns a new VersionVector.
*/
@InternalApi private[akka] def +(node: UniqueAddress): VersionVector = increment(node)
/**
* Increment the version for the node passed as argument. Returns a new VersionVector.
*/
def increment(node: SelfUniqueAddress): VersionVector = increment(node.uniqueAddress)
def isEmpty: Boolean
/**
* INTERNAL API
*/
@InternalApi private[akka] def size: Int
/**
* INTERNAL API
* Increment the version for the node passed as argument. Returns a new VersionVector.
*/
@InternalApi private[akka] def increment(node: UniqueAddress): VersionVector
/**
* INTERNAL API
*/
@InternalApi private[akka] def versionAt(node: UniqueAddress): Long
/**
* INTERNAL API
*/
@InternalApi private[akka] def contains(node: UniqueAddress): Boolean
/**
* Returns true if <code>this</code> and <code>that</code> are concurrent else false.
*/
def <>(that: VersionVector): Boolean = compareOnlyTo(that, Concurrent) eq Concurrent
/**
* Returns true if <code>this</code> is before <code>that</code> else false.
*/
def <(that: VersionVector): Boolean = compareOnlyTo(that, Before) eq Before
/**
* Returns true if <code>this</code> is after <code>that</code> else false.
*/
def >(that: VersionVector): Boolean = compareOnlyTo(that, After) eq After
/**
* Returns true if this VersionVector has the same history as the 'that' VersionVector else false.
*/
def ==(that: VersionVector): Boolean = compareOnlyTo(that, Same) eq Same
/**
* Version vector comparison according to the semantics described by compareTo, with the ability to bail
* out early if the we can't reach the Ordering that we are looking for.
*
* The ordering always starts with Same and can then go to Same, Before or After
* If we're on After we can only go to After or Concurrent
* If we're on Before we can only go to Before or Concurrent
* If we go to Concurrent we exit the loop immediately
*
* If you send in the ordering FullOrder, you will get a full comparison.
*/
private final def compareOnlyTo(that: VersionVector, order: Ordering): Ordering = {
def nextOrElse[A](iter: Iterator[A], default: A): A = if (iter.hasNext) iter.next() else default
def compare(
i1: Iterator[(UniqueAddress, Long)],
i2: Iterator[(UniqueAddress, Long)],
requestedOrder: Ordering): Ordering = {
@tailrec
def compareNext(nt1: (UniqueAddress, Long), nt2: (UniqueAddress, Long), currentOrder: Ordering): Ordering =
if ((requestedOrder ne FullOrder) && (currentOrder ne Same) && (currentOrder ne requestedOrder)) currentOrder
else if ((nt1 eq cmpEndMarker) && (nt2 eq cmpEndMarker)) currentOrder
// i1 is empty but i2 is not, so i1 can only be Before
else if (nt1 eq cmpEndMarker) {
if (currentOrder eq After) Concurrent else Before
}
// i2 is empty but i1 is not, so i1 can only be After
else if (nt2 eq cmpEndMarker) {
if (currentOrder eq Before) Concurrent else After
} else {
// compare the nodes
val nc = nt1._1.compareTo(nt2._1)
if (nc == 0) {
// both nodes exist compare the timestamps
// same timestamp so just continue with the next nodes
if (nt1._2 == nt2._2) compareNext(nextOrElse(i1, cmpEndMarker), nextOrElse(i2, cmpEndMarker), currentOrder)
else if (nt1._2 < nt2._2) {
// t1 is less than t2, so i1 can only be Before
if (currentOrder eq After) Concurrent
else compareNext(nextOrElse(i1, cmpEndMarker), nextOrElse(i2, cmpEndMarker), Before)
} else {
// t2 is less than t1, so i1 can only be After
if (currentOrder eq Before) Concurrent
else compareNext(nextOrElse(i1, cmpEndMarker), nextOrElse(i2, cmpEndMarker), After)
}
} else if (nc < 0) {
// this node only exists in i1 so i1 can only be After
if (currentOrder eq Before) Concurrent
else compareNext(nextOrElse(i1, cmpEndMarker), nt2, After)
} else {
// this node only exists in i2 so i1 can only be Before
if (currentOrder eq After) Concurrent
else compareNext(nt1, nextOrElse(i2, cmpEndMarker), Before)
}
}
compareNext(nextOrElse(i1, cmpEndMarker), nextOrElse(i2, cmpEndMarker), Same)
}
if (this eq that) Same
else compare(this.versionsIterator, that.versionsIterator, if (order eq Concurrent) FullOrder else order)
}
/**
* INTERNAL API
*/
@InternalApi private[akka] def versionsIterator: Iterator[(UniqueAddress, Long)]
/**
* Compare two version vectors. The outcome will be one of the following:
* <p/>
* {{{
* 1. Version 1 is SAME (==) as Version 2 iff for all i c1(i) == c2(i)
* 2. Version 1 is BEFORE (<) Version 2 iff for all i c1(i) <= c2(i) and there exist a j such that c1(j) < c2(j)
* 3. Version 1 is AFTER (>) Version 2 iff for all i c1(i) >= c2(i) and there exist a j such that c1(j) > c2(j).
* 4. Version 1 is CONCURRENT (<>) to Version 2 otherwise.
* }}}
*/
def compareTo(that: VersionVector): Ordering = {
compareOnlyTo(that, FullOrder)
}
/**
* Merges this VersionVector with another VersionVector. E.g. merges its versioned history.
*/
def merge(that: VersionVector): VersionVector
override def needPruningFrom(removedNode: UniqueAddress): Boolean
override def prune(removedNode: UniqueAddress, collapseInto: UniqueAddress): VersionVector
override def pruningCleanup(removedNode: UniqueAddress): VersionVector
/** INTERNAL API */
@InternalApi private[akka] def estimatedSize: Int
}
final case class OneVersionVector private[akka] (node: UniqueAddress, version: Long) extends VersionVector {
import VersionVector.Timestamp
override def isEmpty: Boolean = false
/** INTERNAL API */
@InternalApi private[akka] override def size: Int = 1
/** INTERNAL API */
@InternalApi private[akka] override def increment(n: UniqueAddress): VersionVector = {
val v = Timestamp.counter.getAndIncrement()
if (n == node) copy(version = v)
else ManyVersionVector(TreeMap(node -> version, n -> v))
}
/** INTERNAL API */
@InternalApi private[akka] override def versionAt(n: UniqueAddress): Long =
if (n == node) version
else Timestamp.Zero
/** INTERNAL API */
@InternalApi private[akka] override def contains(n: UniqueAddress): Boolean =
n == node
/** INTERNAL API */
@InternalApi private[akka] override def versionsIterator: Iterator[(UniqueAddress, Long)] =
Iterator.single((node, version))
override def merge(that: VersionVector): VersionVector = {
that match {
case OneVersionVector(n2, v2) =>
if (node == n2) if (version >= v2) this else OneVersionVector(n2, v2)
else ManyVersionVector(TreeMap(node -> version, n2 -> v2))
case ManyVersionVector(vs2) =>
val v2 = vs2.getOrElse(node, Timestamp.Zero)
val mergedVersions =
if (v2 >= version) vs2
else vs2.updated(node, version)
VersionVector(mergedVersions)
}
}
override def modifiedByNodes: Set[UniqueAddress] =
Set(node)
override def needPruningFrom(removedNode: UniqueAddress): Boolean =
node == removedNode
override def prune(removedNode: UniqueAddress, collapseInto: UniqueAddress): VersionVector =
(if (node == removedNode) VersionVector.empty else this) + collapseInto
override def pruningCleanup(removedNode: UniqueAddress): VersionVector =
if (node == removedNode) VersionVector.empty else this
override def toString: String =
s"VersionVector($node -> $version)"
/** INTERNAL API */
@InternalApi override private[akka] def estimatedSize: Int =
EstimatedSize.UniqueAddress + EstimatedSize.LongValue
}
final case class ManyVersionVector(versions: TreeMap[UniqueAddress, Long]) extends VersionVector {
import VersionVector.Timestamp
override def isEmpty: Boolean = versions.isEmpty
/** INTERNAL API */
@InternalApi private[akka] override def size: Int = versions.size
/** INTERNAL API */
@InternalApi private[akka] override def increment(node: UniqueAddress): VersionVector = {
val v = Timestamp.counter.getAndIncrement()
VersionVector(versions.updated(node, v))
}
/** INTERNAL API */
@InternalApi private[akka] override def versionAt(node: UniqueAddress): Long = versions.get(node) match {
case Some(v) => v
case None => Timestamp.Zero
}
/** INTERNAL API */
@InternalApi private[akka] override def contains(node: UniqueAddress): Boolean =
versions.contains(node)
/** INTERNAL API */
@InternalApi private[akka] override def versionsIterator: Iterator[(UniqueAddress, Long)] =
versions.iterator
override def merge(that: VersionVector): VersionVector = {
if (that.isEmpty) this
else if (this.isEmpty) that
else
that match {
case ManyVersionVector(vs2) =>
var mergedVersions = vs2
for ((node, time) <- versions) {
val mergedVersionsCurrentTime = mergedVersions.getOrElse(node, Timestamp.Zero)
if (time > mergedVersionsCurrentTime)
mergedVersions = mergedVersions.updated(node, time)
}
VersionVector(mergedVersions)
case OneVersionVector(n2, v2) =>
val v1 = versions.getOrElse(n2, Timestamp.Zero)
val mergedVersions =
if (v1 >= v2) versions
else versions.updated(n2, v2)
VersionVector(mergedVersions)
}
}
override def modifiedByNodes: Set[UniqueAddress] =
versions.keySet
override def needPruningFrom(removedNode: UniqueAddress): Boolean =
versions.contains(removedNode)
override def prune(removedNode: UniqueAddress, collapseInto: UniqueAddress): VersionVector =
VersionVector(versions = versions - removedNode) + collapseInto
override def pruningCleanup(removedNode: UniqueAddress): VersionVector =
if (versions.contains(removedNode)) VersionVector(versions = versions - removedNode)
else this
override def toString: String =
versions.map { case ((n, v)) => n.toString + " -> " + v }.mkString("VersionVector(", ", ", ")")
/** INTERNAL API */
@InternalApi override private[akka] def estimatedSize: Int =
versions.size * (EstimatedSize.UniqueAddress + EstimatedSize.LongValue)
}