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authorPierre Schmitz <pierre@archlinux.de>2014-12-27 15:41:37 +0100
committerPierre Schmitz <pierre@archlinux.de>2014-12-31 11:43:28 +0100
commitc1f9b1f7b1b77776192048005dcc66dcf3df2bfb (patch)
tree2b38796e738dd74cb42ecd9bfd151803108386bc /includes/HashRing.php
parentb88ab0086858470dd1f644e64cb4e4f62bb2be9b (diff)
Update to MediaWiki 1.24.1
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-<?php
-/**
- * Convenience class for weighted consistent hash rings.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
- * http://www.gnu.org/copyleft/gpl.html
- *
- * @file
- * @author Aaron Schulz
- */
-
-/**
- * Convenience class for weighted consistent hash rings
- *
- * @since 1.22
- */
-class HashRing {
- /** @var Array (location => weight) */
- protected $sourceMap = array();
- /** @var Array (location => (start, end)) */
- protected $ring = array();
-
- const RING_SIZE = 268435456; // 2^28
-
- /**
- * @param array $map (location => weight)
- */
- public function __construct( array $map ) {
- $map = array_filter( $map, function( $w ) { return $w > 0; } );
- if ( !count( $map ) ) {
- throw new MWException( "Ring is empty or all weights are zero." );
- }
- $this->sourceMap = $map;
- // Sort the locations based on the hash of their names
- $hashes = array();
- foreach ( $map as $location => $weight ) {
- $hashes[$location] = sha1( $location );
- }
- uksort( $map, function ( $a, $b ) use ( $hashes ) {
- return strcmp( $hashes[$a], $hashes[$b] );
- } );
- // Fit the map to weight-proportionate one with a space of size RING_SIZE
- $sum = array_sum( $map );
- $standardMap = array();
- foreach ( $map as $location => $weight ) {
- $standardMap[$location] = (int)floor( $weight / $sum * self::RING_SIZE );
- }
- // Build a ring of RING_SIZE spots, with each location at a spot in location hash order
- $index = 0;
- foreach ( $standardMap as $location => $weight ) {
- // Location covers half-closed interval [$index,$index + $weight)
- $this->ring[$location] = array( $index, $index + $weight );
- $index += $weight;
- }
- // Make sure the last location covers what is left
- end( $this->ring );
- $this->ring[key( $this->ring )][1] = self::RING_SIZE;
- }
-
- /**
- * Get the location of an item on the ring
- *
- * @param string $item
- * @return string Location
- */
- public function getLocation( $item ) {
- $locations = $this->getLocations( $item, 1 );
- return $locations[0];
- }
-
- /**
- * Get the location of an item on the ring, as well as the next clockwise locations
- *
- * @param string $item
- * @param integer $limit Maximum number of locations to return
- * @return array List of locations
- */
- public function getLocations( $item, $limit ) {
- $locations = array();
- $primaryLocation = null;
- $spot = hexdec( substr( sha1( $item ), 0, 7 ) ); // first 28 bits
- foreach ( $this->ring as $location => $range ) {
- if ( count( $locations ) >= $limit ) {
- break;
- }
- // The $primaryLocation is the location the item spot is in.
- // After that is reached, keep appending the next locations.
- if ( ( $range[0] <= $spot && $spot < $range[1] ) || $primaryLocation !== null ) {
- if ( $primaryLocation === null ) {
- $primaryLocation = $location;
- }
- $locations[] = $location;
- }
- }
- // If more locations are requested, wrap-around and keep adding them
- reset( $this->ring );
- while ( count( $locations ) < $limit ) {
- list( $location, ) = each( $this->ring );
- if ( $location === $primaryLocation ) {
- break; // don't go in circles
- }
- $locations[] = $location;
- }
- return $locations;
- }
-
- /**
- * Get the map of locations to weight (ignores 0-weight items)
- *
- * @return array
- */
- public function getLocationWeights() {
- return $this->sourceMap;
- }
-
- /**
- * Get a new hash ring with a location removed from the ring
- *
- * @param string $location
- * @return HashRing|bool Returns false if no non-zero weighted spots are left
- */
- public function newWithoutLocation( $location ) {
- $map = $this->sourceMap;
- unset( $map[$location] );
- if ( count( $map ) ) {
- return new self( $map );
- }
- return false;
- }
-}