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<?php
/**
* Classes to cache objects in PHP accelerators, SQL database or DBA files
*
* Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
* http://www.mediawiki.org/
*
* 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
* @ingroup Cache
*/
/**
* @defgroup Cache Cache
*/
/**
* interface is intended to be more or less compatible with
* the PHP memcached client.
*
* backends for local hash array and SQL table included:
* <code>
* $bag = new HashBagOStuff();
* $bag = new SqlBagOStuff(); # connect to db first
* </code>
*
* @ingroup Cache
*/
abstract class BagOStuff {
private $debugMode = false;
/**
* @param $bool bool
*/
public function setDebug( $bool ) {
$this->debugMode = $bool;
}
/* *** THE GUTS OF THE OPERATION *** */
/* Override these with functional things in subclasses */
/**
* Get an item with the given key. Returns false if it does not exist.
* @param $key string
* @param $casToken[optional] mixed
* @return mixed Returns false on failure
*/
abstract public function get( $key, &$casToken = null );
/**
* Set an item.
* @param $key string
* @param $value mixed
* @param int $exptime Either an interval in seconds or a unix timestamp for expiry
* @return bool success
*/
abstract public function set( $key, $value, $exptime = 0 );
/**
* Check and set an item.
* @param $casToken mixed
* @param $key string
* @param $value mixed
* @param int $exptime Either an interval in seconds or a unix timestamp for expiry
* @return bool success
*/
abstract public function cas( $casToken, $key, $value, $exptime = 0 );
/**
* Delete an item.
* @param $key string
* @param int $time Amount of time to delay the operation (mostly memcached-specific)
* @return bool True if the item was deleted or not found, false on failure
*/
abstract public function delete( $key, $time = 0 );
/**
* Merge changes into the existing cache value (possibly creating a new one).
* The callback function returns the new value given the current value (possibly false),
* and takes the arguments: (this BagOStuff object, cache key, current value).
*
* @param $key string
* @param $callback closure Callback method to be executed
* @param int $exptime Either an interval in seconds or a unix timestamp for expiry
* @param int $attempts The amount of times to attempt a merge in case of failure
* @return bool success
*/
public function merge( $key, closure $callback, $exptime = 0, $attempts = 10 ) {
return $this->mergeViaCas( $key, $callback, $exptime, $attempts );
}
/**
* @see BagOStuff::merge()
*
* @param $key string
* @param $callback closure Callback method to be executed
* @param int $exptime Either an interval in seconds or a unix timestamp for expiry
* @param int $attempts The amount of times to attempt a merge in case of failure
* @return bool success
*/
protected function mergeViaCas( $key, closure $callback, $exptime = 0, $attempts = 10 ) {
do {
$casToken = null; // passed by reference
$currentValue = $this->get( $key, $casToken ); // get the old value
$value = $callback( $this, $key, $currentValue ); // derive the new value
if ( $value === false ) {
$success = true; // do nothing
} elseif ( $currentValue === false ) {
// Try to create the key, failing if it gets created in the meantime
$success = $this->add( $key, $value, $exptime );
} else {
// Try to update the key, failing if it gets changed in the meantime
$success = $this->cas( $casToken, $key, $value, $exptime );
}
} while ( !$success && --$attempts );
return $success;
}
/**
* @see BagOStuff::merge()
*
* @param $key string
* @param $callback closure Callback method to be executed
* @param int $exptime Either an interval in seconds or a unix timestamp for expiry
* @param int $attempts The amount of times to attempt a merge in case of failure
* @return bool success
*/
protected function mergeViaLock( $key, closure $callback, $exptime = 0, $attempts = 10 ) {
if ( !$this->lock( $key, 60 ) ) {
return false;
}
$currentValue = $this->get( $key ); // get the old value
$value = $callback( $this, $key, $currentValue ); // derive the new value
if ( $value === false ) {
$success = true; // do nothing
} else {
$success = $this->set( $key, $value, $exptime ); // set the new value
}
if ( !$this->unlock( $key ) ) {
// this should never happen
trigger_error( "Could not release lock for key '$key'." );
}
return $success;
}
/**
* @param $key string
* @param $timeout integer [optional]
* @return bool success
*/
public function lock( $key, $timeout = 60 ) {
$timestamp = microtime( true ); // starting UNIX timestamp
if ( $this->add( "{$key}:lock", $timeout ) ) {
return true;
}
$uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
$sleep = 2*$uRTT; // rough time to do get()+set()
$locked = false; // lock acquired
$attempts = 0; // failed attempts
do {
if ( ++$attempts >= 3 && $sleep <= 1e6 ) {
// Exponentially back off after failed attempts to avoid network spam.
// About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
$sleep *= 2;
}
usleep( $sleep ); // back off
$locked = $this->add( "{$key}:lock", $timeout );
} while( !$locked );
return $locked;
}
/**
* @param $key string
* @return bool success
*/
public function unlock( $key ) {
return $this->delete( "{$key}:lock" );
}
/**
* Delete all objects expiring before a certain date.
* @param string $date The reference date in MW format
* @param $progressCallback callback|bool Optional, a function which will be called
* regularly during long-running operations with the percentage progress
* as the first parameter.
*
* @return bool on success, false if unimplemented
*/
public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
// stub
return false;
}
/* *** Emulated functions *** */
/**
* Get an associative array containing the item for each of the keys that have items.
* @param array $keys List of strings
* @return Array
*/
public function getMulti( array $keys ) {
$res = array();
foreach ( $keys as $key ) {
$val = $this->get( $key );
if ( $val !== false ) {
$res[$key] = $val;
}
}
return $res;
}
/**
* @param $key string
* @param $value mixed
* @param $exptime integer
* @return bool success
*/
public function add( $key, $value, $exptime = 0 ) {
if ( $this->get( $key ) === false ) {
return $this->set( $key, $value, $exptime );
}
return false; // key already set
}
/**
* @param $key string
* @param $value mixed
* @param $exptime int
* @return bool success
*/
public function replace( $key, $value, $exptime = 0 ) {
if ( $this->get( $key ) !== false ) {
return $this->set( $key, $value, $exptime );
}
return false; // key not already set
}
/**
* Increase stored value of $key by $value while preserving its TTL
* @param string $key Key to increase
* @param $value Integer: Value to add to $key (Default 1)
* @return integer|bool New value or false on failure
*/
public function incr( $key, $value = 1 ) {
if ( !$this->lock( $key ) ) {
return false;
}
$n = $this->get( $key );
if ( $this->isInteger( $n ) ) { // key exists?
$n += intval( $value );
$this->set( $key, max( 0, $n ) ); // exptime?
} else {
$n = false;
}
$this->unlock( $key );
return $n;
}
/**
* Decrease stored value of $key by $value while preserving its TTL
* @param $key String
* @param $value Integer
* @return integer
*/
public function decr( $key, $value = 1 ) {
return $this->incr( $key, - $value );
}
/**
* @param $text string
*/
public function debug( $text ) {
if ( $this->debugMode ) {
$class = get_class( $this );
wfDebug( "$class debug: $text\n" );
}
}
/**
* Convert an optionally relative time to an absolute time
* @param $exptime integer
* @return int
*/
protected function convertExpiry( $exptime ) {
if ( ( $exptime != 0 ) && ( $exptime < 86400 * 3650 /* 10 years */ ) ) {
return time() + $exptime;
} else {
return $exptime;
}
}
/**
* Convert an optionally absolute expiry time to a relative time. If an
* absolute time is specified which is in the past, use a short expiry time.
*
* @param $exptime integer
* @return integer
*/
protected function convertToRelative( $exptime ) {
if ( $exptime >= 86400 * 3650 /* 10 years */ ) {
$exptime -= time();
if ( $exptime <= 0 ) {
$exptime = 1;
}
return $exptime;
} else {
return $exptime;
}
}
/**
* Check if a value is an integer
*
* @param $value mixed
* @return bool
*/
protected function isInteger( $value ) {
return ( is_int( $value ) || ctype_digit( $value ) );
}
}