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<?php
/**
* 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
*/
namespace MediaWiki\PoolCounter;
use Exception;
use MediaWiki\Status\Status;
use RedisException;
use Wikimedia\ArrayUtils\ArrayUtils;
use Wikimedia\HashRing\HashRing;
use Wikimedia\ObjectCache\RedisConnectionPool;
use Wikimedia\ObjectCache\RedisConnRef;
/**
* Version of PoolCounter that uses Redis
*
* There are four main redis keys used to track each pool counter key:
* - poolcounter:l-slots-* : A list of available slot IDs for a pool.
* - poolcounter:z-renewtime-* : A sorted set of (slot ID, UNIX timestamp as score)
* used for tracking the next time a slot should be
* released. This is -1 when a slot is created, and is
* set when released (expired), locked, and unlocked.
* - poolcounter:z-wait-* : A sorted set of (slot ID, UNIX timestamp as score)
* used for tracking waiting processes (and wait time).
* - poolcounter:l-wakeup-* : A list pushed to for the sake of waking up processes
* when a any process in the pool finishes (lasts for 1ms).
*
* For a given pool key, all the redis keys start off non-existing and are deleted if not
* used for a while to prevent garbage from building up on the server. They are atomically
* re-initialized as needed. The "z-renewtime" key is used for detecting sessions which got
* slots but then disappeared. Stale entries from there have their timestamp updated and the
* corresponding slots freed up. The "z-wait" key is used for detecting processes registered
* as waiting but that disappeared. Stale entries from there are deleted and the corresponding
* slots are freed up. The worker count is included in all the redis key names as it does not
* vary within each $wgPoolCounterConf type and doing so handles configuration changes.
*
* This class requires Redis 2.6 as it makes use Lua scripts for fast atomic operations.
* Also this should be on a server plenty of RAM for the working set to avoid evictions.
* Evictions could temporarily allow wait queues to double in size or temporarily cause
* pools to appear as full when they are not. Using volatile-ttl and bumping memory-samples
* in redis.conf can be helpful otherwise.
*
* @since 1.23
*/
class PoolCounterRedis extends PoolCounter {
/** @var HashRing */
protected $ring;
/** @var RedisConnectionPool */
protected $pool;
/** @var array (server label => host) map */
protected $serversByLabel;
/** @var string SHA-1 of the key */
protected $keySha1;
/** @var int TTL for locks to expire (work should finish in this time) */
protected $lockTTL;
/** @var RedisConnRef|null */
protected $conn;
/** @var string|null Pool slot value */
protected $slot;
/** @var int|null AWAKE_* constant */
protected $onRelease;
/** @var string Unique string to identify this process */
protected $session;
/** @var float|null UNIX timestamp */
protected $slotTime;
private const AWAKE_ONE = 1; // wake-up if when a slot can be taken from an existing process
private const AWAKE_ALL = 2; // wake-up if an existing process finishes and wake up such others
/** @var PoolCounterRedis[] List of active PoolCounterRedis objects in this script */
protected static $active = null;
public function __construct( $conf, $type, $key ) {
parent::__construct( $conf, $type, $key );
$this->serversByLabel = $conf['servers'];
$serverLabels = array_keys( $conf['servers'] );
$this->ring = new HashRing( array_fill_keys( $serverLabels, 10 ) );
$conf['redisConfig']['serializer'] = 'none'; // for use with Lua
$this->pool = RedisConnectionPool::singleton( $conf['redisConfig'] );
$this->keySha1 = sha1( $this->key );
$met = ini_get( 'max_execution_time' ); // usually 0 in CLI mode
$this->lockTTL = $met ? 2 * (int)$met : 3600;
if ( self::$active === null ) {
self::$active = [];
register_shutdown_function( [ __CLASS__, 'releaseAll' ] );
}
}
/**
* @return Status Uses RediConnRef as value on success
*/
protected function getConnection() {
if ( !$this->conn ) {
$conn = false;
$servers = $this->ring->getLocations( $this->key, 3 );
ArrayUtils::consistentHashSort( $servers, $this->key );
foreach ( $servers as $server ) {
$conn = $this->pool->getConnection( $this->serversByLabel[$server], $this->logger );
if ( $conn ) {
break;
}
}
if ( !$conn ) {
return Status::newFatal( 'pool-servererror', implode( ', ', $servers ) );
}
$this->conn = $conn;
}
return Status::newGood( $this->conn );
}
public function acquireForMe( $timeout = null ) {
$status = $this->precheckAcquire();
if ( !$status->isGood() ) {
return $status;
}
return $this->waitForSlotOrNotif( self::AWAKE_ONE, $timeout );
}
public function acquireForAnyone( $timeout = null ) {
$status = $this->precheckAcquire();
if ( !$status->isGood() ) {
return $status;
}
return $this->waitForSlotOrNotif( self::AWAKE_ALL, $timeout );
}
public function release() {
if ( $this->slot === null ) {
return Status::newGood( PoolCounter::NOT_LOCKED ); // not locked
}
$status = $this->getConnection();
if ( !$status->isOK() ) {
return $status;
}
/** @var RedisConnRef $conn */
$conn = $status->value;
'@phan-var RedisConnRef $conn';
// phpcs:disable Generic.Files.LineLength
static $script =
/** @lang Lua */
<<<LUA
local kSlots,kSlotsNextRelease,kWakeup,kWaiting = unpack(KEYS)
local rMaxWorkers,rExpiry,rSlot,rSlotTime,rAwakeAll,rTime = unpack(ARGV)
-- Add the slots back to the list (if rSlot is "w" then it is not a slot).
-- Treat the list as expired if the "next release" time sorted-set is missing.
if rSlot ~= 'w' and redis.call('exists',kSlotsNextRelease) == 1 then
if 1*redis.call('zScore',kSlotsNextRelease,rSlot) ~= (rSlotTime + rExpiry) then
-- Slot lock expired and was released already
elseif redis.call('lLen',kSlots) >= 1*rMaxWorkers then
-- Slots somehow got out of sync; reset the list
redis.call('del',kSlots,kSlotsNextRelease)
elseif redis.call('lLen',kSlots) == (1*rMaxWorkers - 1) and redis.call('zCard',kWaiting) == 0 then
-- Slot list will be made full; clear it to save space (it re-inits as needed)
-- since nothing is waiting on being unblocked by a push to the list
redis.call('del',kSlots,kSlotsNextRelease)
else
-- Add slot back to pool and update the "next release" time
redis.call('rPush',kSlots,rSlot)
redis.call('zAdd',kSlotsNextRelease,rTime + 30,rSlot)
-- Always keep renewing the expiry on use
redis.call('expireAt',kSlots,math.ceil(rTime + rExpiry))
redis.call('expireAt',kSlotsNextRelease,math.ceil(rTime + rExpiry))
end
end
-- Update an ephemeral list to wake up other clients that can
-- reuse any cached work from this process. Only do this if no
-- slots are currently free (e.g. clients could be waiting).
if 1*rAwakeAll == 1 then
local count = redis.call('zCard',kWaiting)
for i = 1,count do
redis.call('rPush',kWakeup,'w')
end
redis.call('pexpire',kWakeup,1)
end
return 1
LUA;
// phpcs:enable
try {
$conn->luaEval(
$script,
[
$this->getSlotListKey(),
$this->getSlotRTimeSetKey(),
$this->getWakeupListKey(),
$this->getWaitSetKey(),
$this->workers,
$this->lockTTL,
$this->slot,
$this->slotTime, // used for CAS-style check
( $this->onRelease === self::AWAKE_ALL ) ? 1 : 0,
microtime( true ),
],
4 # number of first argument(s) that are keys
);
} catch ( RedisException $e ) {
return Status::newFatal( 'pool-error-unknown', $e->getMessage() );
}
$this->slot = null;
$this->slotTime = null;
$this->onRelease = null;
unset( self::$active[$this->session] );
$this->onRelease();
return Status::newGood( PoolCounter::RELEASED );
}
/**
* @param int $doWakeup AWAKE_* constant
* @param int|float|null $timeout
* @return Status
*/
protected function waitForSlotOrNotif( $doWakeup, $timeout = null ) {
if ( $this->slot !== null ) {
return Status::newGood( PoolCounter::LOCK_HELD ); // already acquired
}
$status = $this->getConnection();
if ( !$status->isOK() ) {
return $status;
}
/** @var RedisConnRef $conn */
$conn = $status->value;
'@phan-var RedisConnRef $conn';
$now = microtime( true );
$timeout ??= $this->timeout;
try {
$slot = $this->initAndPopPoolSlotList( $conn, $now );
if ( ctype_digit( $slot ) ) {
// Pool slot acquired by this process
$slotTime = $now;
} elseif ( $slot === 'QUEUE_FULL' ) {
// Too many processes are waiting for pooled processes to finish
return Status::newGood( PoolCounter::QUEUE_FULL );
} elseif ( $slot === 'QUEUE_WAIT' ) {
// This process is now registered as waiting
$keys =
( $doWakeup == self::AWAKE_ALL ) // Wait for an open slot or wake-up signal (preferring the latter)
? [ $this->getWakeupListKey(), $this->getSlotListKey() ] // Just wait for an actual pool slot
: [ $this->getSlotListKey() ];
$res = $conn->blPop( $keys, $timeout );
if ( $res === [] ) {
$conn->zRem( $this->getWaitSetKey(), $this->session ); // no longer waiting
return Status::newGood( PoolCounter::TIMEOUT );
}
$slot = $res[1]; // pool slot or "w" for wake-up notifications
$slotTime = microtime( true ); // last microtime() was a few RTTs ago
// Unregister this process as waiting and bump slot "next release" time
$this->registerAcquisitionTime( $conn, $slot, $slotTime );
} else {
return Status::newFatal( 'pool-error-unknown', "Server gave slot '$slot'." );
}
} catch ( RedisException $e ) {
return Status::newFatal( 'pool-error-unknown', $e->getMessage() );
}
if ( $slot !== 'w' ) {
$this->slot = $slot;
$this->slotTime = $slotTime;
$this->onRelease = $doWakeup;
self::$active[$this->session] = $this;
}
$this->onAcquire();
return Status::newGood( $slot === 'w' ? PoolCounter::DONE : PoolCounter::LOCKED );
}
/**
* @param RedisConnRef $conn
* @param float $now UNIX timestamp
* @return string|bool False on failure
*/
protected function initAndPopPoolSlotList( RedisConnRef $conn, $now ) {
static $script = /** @lang Lua */ <<<LUA
local kSlots,kSlotsNextRelease,kSlotWaits = unpack(KEYS)
local rMaxWorkers,rMaxQueue,rTimeout,rExpiry,rSess,rTime = unpack(ARGV)
-- Initialize if the "next release" time sorted-set is empty. The slot key
-- itself is empty if all slots are busy or when nothing is initialized.
-- If the list is empty but the set is not, then it is the latter case.
-- If the list exists but not the set, then reset everything.
if redis.call('exists',kSlotsNextRelease) == 0 then
redis.call('del',kSlots)
for i = 1,1*rMaxWorkers do
redis.call('rPush',kSlots,i)
redis.call('zAdd',kSlotsNextRelease,-1,i)
end
-- Otherwise do maintenance to clean up after network partitions
else
-- Find stale slot locks and add free them (avoid duplicates)
local staleLocks = redis.call('zRangeByScore',kSlotsNextRelease,0,rTime)
for k,slot in ipairs(staleLocks) do
redis.call('lRem',kSlots,0,slot)
redis.call('rPush',kSlots,slot)
redis.call('zAdd',kSlotsNextRelease,rTime + 30,slot)
end
-- Find stale wait slot entries and remove them
redis.call('zRemRangeByScore',kSlotWaits,0,rTime - 2*rTimeout)
end
local slot
-- Try to acquire a slot if possible now
if redis.call('lLen',kSlots) > 0 then
slot = redis.call('lPop',kSlots)
-- Update the slot "next release" time
redis.call('zAdd',kSlotsNextRelease,rTime + rExpiry,slot)
elseif redis.call('zCard',kSlotWaits) >= 1*rMaxQueue then
slot = 'QUEUE_FULL'
else
slot = 'QUEUE_WAIT'
-- Register this process as waiting
redis.call('zAdd',kSlotWaits,rTime,rSess)
redis.call('expireAt',kSlotWaits,math.ceil(rTime + 2*rTimeout))
end
-- Always keep renewing the expiry on use
redis.call('expireAt',kSlots,math.ceil(rTime + rExpiry))
redis.call('expireAt',kSlotsNextRelease,math.ceil(rTime + rExpiry))
return slot
LUA;
return $conn->luaEval(
$script,
[
$this->getSlotListKey(),
$this->getSlotRTimeSetKey(),
$this->getWaitSetKey(),
$this->workers,
$this->maxqueue,
$this->timeout,
$this->lockTTL,
$this->session,
$now,
],
3 # number of first argument(s) that are keys
);
}
/**
* @param RedisConnRef $conn
* @param string $slot
* @param float $now
* @return int|bool False on failure
*/
protected function registerAcquisitionTime( RedisConnRef $conn, $slot, $now ) {
static $script = /** @lang Lua */ <<<LUA
local kSlots,kSlotsNextRelease,kSlotWaits = unpack(KEYS)
local rSlot,rExpiry,rSess,rTime = unpack(ARGV)
-- If rSlot is 'w' then the client was told to wake up but got no slot
if rSlot ~= 'w' then
-- Update the slot "next release" time
redis.call('zAdd',kSlotsNextRelease,rTime + rExpiry,rSlot)
-- Always keep renewing the expiry on use
redis.call('expireAt',kSlots,math.ceil(rTime + rExpiry))
redis.call('expireAt',kSlotsNextRelease,math.ceil(rTime + rExpiry))
end
-- Unregister this process as waiting
redis.call('zRem',kSlotWaits,rSess)
return 1
LUA;
return $conn->luaEval(
$script,
[
$this->getSlotListKey(),
$this->getSlotRTimeSetKey(),
$this->getWaitSetKey(),
$slot,
$this->lockTTL,
$this->session,
$now,
],
3 # number of first argument(s) that are keys
);
}
/**
* @return string
*/
protected function getSlotListKey() {
return "poolcounter:l-slots-{$this->keySha1}-{$this->workers}";
}
/**
* @return string
*/
protected function getSlotRTimeSetKey() {
return "poolcounter:z-renewtime-{$this->keySha1}-{$this->workers}";
}
/**
* @return string
*/
protected function getWaitSetKey() {
return "poolcounter:z-wait-{$this->keySha1}-{$this->workers}";
}
/**
* @return string
*/
protected function getWakeupListKey() {
return "poolcounter:l-wakeup-{$this->keySha1}-{$this->workers}";
}
/**
* Try to make sure that locks get released (even with exceptions and fatals)
*/
public static function releaseAll() {
$e = null;
foreach ( self::$active as $poolCounter ) {
try {
if ( $poolCounter->slot !== null ) {
$poolCounter->release();
}
} catch ( Exception $e ) {
}
}
if ( $e ) {
throw $e;
}
}
}
/** @deprecated class alias since 1.42 */
class_alias( PoolCounterRedis::class, 'PoolCounterRedis' );