akka.routing.ConsistentHash.scala Maven / Gradle / Ivy
/**
* Copyright (C) 2009-2012 Typesafe Inc.
*/
package akka.routing
import scala.collection.immutable.{ TreeSet, Seq }
import scala.collection.mutable.{ Buffer, Map }
// =============================================================================================
// Adapted from HashRing.scala in Debasish Ghosh's Redis Client, licensed under Apache 2 license
// =============================================================================================
/**
* Consistent Hashing node ring abstraction.
*
* Not thread-safe, to be used from within an Actor or protected some other way.
*/
class ConsistentHash[T](nodes: Seq[T], replicas: Int) {
private val cluster = Buffer[T]()
private var sortedKeys = TreeSet[Long]()
private var ring = Map[Long, T]()
nodes.foreach(this += _)
def +=(node: T) {
cluster += node
(1 to replicas) foreach { replica ⇒
val key = hashFor((node + ":" + replica).getBytes("UTF-8"))
ring += (key -> node)
sortedKeys = sortedKeys + key
}
}
def -=(node: T) {
cluster -= node
(1 to replicas) foreach { replica ⇒
val key = hashFor((node + ":" + replica).getBytes("UTF-8"))
ring -= key
sortedKeys = sortedKeys - key
}
}
def nodeFor(key: Array[Byte]): T = {
val hash = hashFor(key)
if (sortedKeys contains hash) ring(hash)
else {
if (hash < sortedKeys.firstKey) ring(sortedKeys.firstKey)
else if (hash > sortedKeys.lastKey) ring(sortedKeys.lastKey)
else ring(sortedKeys.rangeImpl(None, Some(hash)).lastKey)
}
}
private def hashFor(bytes: Array[Byte]): Long = {
val hash = MurmurHash.arrayHash(bytes)
if (hash == Int.MinValue) hash + 1
math.abs(hash)
}
}
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
/**
* An implementation of Austin Appleby's MurmurHash 3.0 algorithm
* (32 bit version); reference: http://code.google.com/p/smhasher
*
* This is the hash used by collections and case classes (including
* tuples).
*
* @author Rex Kerr
* @version 2.9
* @since 2.9
*/
import java.lang.Integer.{ rotateLeft ⇒ rotl }
/**
* A class designed to generate well-distributed non-cryptographic
* hashes. It is designed to be passed to a collection's foreach method,
* or can take individual hash values with append. Its own hash code is
* set equal to the hash code of whatever it is hashing.
*/
class MurmurHash[@specialized(Int, Long, Float, Double) T](seed: Int) extends (T ⇒ Unit) {
import MurmurHash._
private var h = startHash(seed)
private var c = hiddenMagicA
private var k = hiddenMagicB
private var hashed = false
private var hashvalue = h
/** Begin a new hash using the same seed. */
def reset() {
h = startHash(seed)
c = hiddenMagicA
k = hiddenMagicB
hashed = false
}
/** Incorporate the hash value of one item. */
def apply(t: T) {
h = extendHash(h, t.##, c, k)
c = nextMagicA(c)
k = nextMagicB(k)
hashed = false
}
/** Incorporate a known hash value. */
def append(i: Int) {
h = extendHash(h, i, c, k)
c = nextMagicA(c)
k = nextMagicB(k)
hashed = false
}
/** Retrieve the hash value */
def hash = {
if (!hashed) {
hashvalue = finalizeHash(h)
hashed = true
}
hashvalue
}
override def hashCode = hash
}
/**
* An object designed to generate well-distributed non-cryptographic
* hashes. It is designed to hash a collection of integers; along with
* the integers to hash, it generates two magic streams of integers to
* increase the distribution of repetitive input sequences. Thus,
* three methods need to be called at each step (to start and to
* incorporate a new integer) to update the values. Only one method
* needs to be called to finalize the hash.
*/
object MurmurHash {
// Magic values used for MurmurHash's 32 bit hash.
// Don't change these without consulting a hashing expert!
final private val visibleMagic = 0x971e137b
final private val hiddenMagicA = 0x95543787
final private val hiddenMagicB = 0x2ad7eb25
final private val visibleMixer = 0x52dce729
final private val hiddenMixerA = 0x7b7d159c
final private val hiddenMixerB = 0x6bce6396
final private val finalMixer1 = 0x85ebca6b
final private val finalMixer2 = 0xc2b2ae35
// Arbitrary values used for hashing certain classes
final private val seedString = 0xf7ca7fd2
final private val seedArray = 0x3c074a61
/** The first 23 magic integers from the first stream are stored here */
val storedMagicA =
Iterator.iterate(hiddenMagicA)(nextMagicA).take(23).toArray
/** The first 23 magic integers from the second stream are stored here */
val storedMagicB =
Iterator.iterate(hiddenMagicB)(nextMagicB).take(23).toArray
/** Begin a new hash with a seed value. */
def startHash(seed: Int) = seed ^ visibleMagic
/** The initial magic integers in the first stream. */
def startMagicA = hiddenMagicA
/** The initial magic integer in the second stream. */
def startMagicB = hiddenMagicB
/**
* Incorporates a new value into an existing hash.
*
* @param hash the prior hash value
* @param value the new value to incorporate
* @param magicA a magic integer from the stream
* @param magicB a magic integer from a different stream
* @return the updated hash value
*/
def extendHash(hash: Int, value: Int, magicA: Int, magicB: Int) = {
(hash ^ rotl(value * magicA, 11) * magicB) * 3 + visibleMixer
}
/** Given a magic integer from the first stream, compute the next */
def nextMagicA(magicA: Int) = magicA * 5 + hiddenMixerA
/** Given a magic integer from the second stream, compute the next */
def nextMagicB(magicB: Int) = magicB * 5 + hiddenMixerB
/** Once all hashes have been incorporated, this performs a final mixing */
def finalizeHash(hash: Int) = {
var i = (hash ^ (hash >>> 16))
i *= finalMixer1
i ^= (i >>> 13)
i *= finalMixer2
i ^= (i >>> 16)
i
}
/** Compute a high-quality hash of an array */
def arrayHash[@specialized T](a: Array[T]) = {
var h = startHash(a.length * seedArray)
var c = hiddenMagicA
var k = hiddenMagicB
var j = 0
while (j < a.length) {
h = extendHash(h, a(j).##, c, k)
c = nextMagicA(c)
k = nextMagicB(k)
j += 1
}
finalizeHash(h)
}
/** Compute a high-quality hash of a string */
def stringHash(s: String) = {
var h = startHash(s.length * seedString)
var c = hiddenMagicA
var k = hiddenMagicB
var j = 0
while (j + 1 < s.length) {
val i = (s.charAt(j) << 16) + s.charAt(j + 1);
h = extendHash(h, i, c, k)
c = nextMagicA(c)
k = nextMagicB(k)
j += 2
}
if (j < s.length) h = extendHash(h, s.charAt(j), c, k)
finalizeHash(h)
}
/**
* Compute a hash that is symmetric in its arguments--that is,
* where the order of appearance of elements does not matter.
* This is useful for hashing sets, for example.
*/
def symmetricHash[T](xs: TraversableOnce[T], seed: Int) = {
var a, b, n = 0
var c = 1
xs.foreach(i ⇒ {
val h = i.##
a += h
b ^= h
if (h != 0) c *= h
n += 1
})
var h = startHash(seed * n)
h = extendHash(h, a, storedMagicA(0), storedMagicB(0))
h = extendHash(h, b, storedMagicA(1), storedMagicB(1))
h = extendHash(h, c, storedMagicA(2), storedMagicB(2))
finalizeHash(h)
}
}
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