MultiWriteBagOStuff.php

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<?php
use Wikimedia\ObjectFactory\ObjectFactory;
 
class MultiWriteBagOStuff extends BagOStuff {
    protected $caches;
 
    protected $asyncWrites = false;
    protected $cacheIndexes = [];
 
    private static $UPGRADE_TTL = 3600;
 
    public function __construct( $params ) {
        parent::__construct( $params );
 
        if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
            throw new InvalidArgumentException(
                __METHOD__ . ': "caches" parameter must be an array of caches'
            );
        }
 
        $this->caches = [];
        foreach ( $params['caches'] as $cacheInfo ) {
            if ( $cacheInfo instanceof BagOStuff ) {
                $this->caches[] = $cacheInfo;
            } else {
                $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
            }
        }
 
        $this->attrMap = $this->mergeFlagMaps( $this->caches );
 
        $this->asyncWrites = (
            isset( $params['replication'] ) &&
            $params['replication'] === 'async' &&
            is_callable( $this->asyncHandler )
        );
 
        $this->cacheIndexes = array_keys( $this->caches );
    }
 
    public function get( $key, $flags = 0 ) {
        $args = func_get_args();
 
        if ( $this->fieldHasFlags( $flags, self::READ_LATEST ) ) {
            // If the latest write was a delete(), we do NOT want to fallback
            // to the other tiers and possibly see the old value. Also, this
            // is used by merge(), which only needs to hit the primary.
            return $this->callKeyMethodOnTierCache(
                0,
                __FUNCTION__,
                self::ARG0_KEY,
                self::RES_NONKEY,
                $args
            );
        }
 
        $value = false;
        // backends checked
        $missIndexes = [];
        foreach ( $this->cacheIndexes as $i ) {
            $value = $this->callKeyMethodOnTierCache(
                $i,
                __FUNCTION__,
                self::ARG0_KEY,
                self::RES_NONKEY,
                $args
            );
            if ( $value !== false ) {
                break;
            }
            $missIndexes[] = $i;
        }
 
        if (
            $value !== false &&
            $this->fieldHasFlags( $flags, self::READ_VERIFIED ) &&
            $missIndexes
        ) {
            // Backfill the value to the higher (and often faster/smaller) cache tiers
            $this->callKeyWriteMethodOnTierCaches(
                $missIndexes,
                'set',
                self::ARG0_KEY,
                self::RES_NONKEY,
                [ $key, $value, self::$UPGRADE_TTL ]
            );
        }
 
        return $value;
    }
 
    public function set( $key, $value, $exptime = 0, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function delete( $key, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function add( $key, $value, $exptime = 0, $flags = 0 ) {
        // Try the write to the top-tier cache
        $ok = $this->callKeyMethodOnTierCache(
            0,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
 
        if ( $ok ) {
            // Relay the add() using set() if it succeeded. This is meant to handle certain
            // migration scenarios where the same store might get written to twice for certain
            // keys. In that case, it makes no sense to return false due to "self-conflicts".
            $okSecondaries = $this->callKeyWriteMethodOnTierCaches(
                array_slice( $this->cacheIndexes, 1 ),
                'set',
                self::ARG0_KEY,
                self::RES_NONKEY,
                [ $key, $value, $exptime, $flags ]
            );
            if ( $okSecondaries === false ) {
                $ok = false;
            }
        }
 
        return $ok;
    }
 
    public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function lock( $key, $timeout = 6, $exptime = 6, $rclass = '' ) {
        // Only need to lock the first cache; also avoids deadlocks
        return $this->callKeyMethodOnTierCache(
            0,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function unlock( $key ) {
        // Only the first cache is locked
        return $this->callKeyMethodOnTierCache(
            0,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function deleteObjectsExpiringBefore(
        $timestamp,
        callable $progress = null,
        $limit = INF,
        string $tag = null
    ) {
        $ret = false;
        foreach ( $this->caches as $cache ) {
            if ( $cache->deleteObjectsExpiringBefore( $timestamp, $progress, $limit, $tag ) ) {
                $ret = true;
            }
        }
 
        return $ret;
    }
 
    public function getMulti( array $keys, $flags = 0 ) {
        // Just iterate over each key in order to handle all the backfill logic
        $res = [];
        foreach ( $keys as $key ) {
            $val = $this->get( $key, $flags );
            if ( $val !== false ) {
                $res[$key] = $val;
            }
        }
 
        return $res;
    }
 
    public function setMulti( array $valueByKey, $exptime = 0, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEYMAP,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function deleteMulti( array $keys, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEYARR,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEYARR,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    public function incrWithInit( $key, $exptime, $step = 1, $init = null, $flags = 0 ) {
        return $this->callKeyWriteMethodOnTierCaches(
            $this->cacheIndexes,
            __FUNCTION__,
            self::ARG0_KEY,
            self::RES_NONKEY,
            func_get_args()
        );
    }
 
    protected function makeKeyInternal( $keyspace, $components ) {
        return $this->genericKeyFromComponents( $keyspace, ...$components );
    }
 
    public function makeKey( $collection, ...$components ) {
        return $this->genericKeyFromComponents( $this->keyspace, $collection, ...$components );
    }
 
    public function makeGlobalKey( $collection, ...$components ) {
        return $this->genericKeyFromComponents( self::GLOBAL_KEYSPACE, $collection, ...$components );
    }
 
    protected function convertGenericKey( $key ) {
        // short-circuit; already uses "generic" keys
        return $key;
    }
 
    public function addBusyCallback( callable $workCallback ) {
        $this->caches[0]->addBusyCallback( $workCallback );
    }
 
    public function setMockTime( &$time ) {
        parent::setMockTime( $time );
        foreach ( $this->caches as $cache ) {
            $cache->setMockTime( $time );
        }
    }
 
    private function callKeyMethodOnTierCache( $index, $method, $arg0Sig, $rvSig, array $args ) {
        return $this->caches[$index]->proxyCall( $method, $arg0Sig, $rvSig, $args, $this );
    }
 
    private function callKeyWriteMethodOnTierCaches(
        array $indexes,
        $method,
        $arg0Sig,
        $resSig,
        array $args
    ) {
        $res = null;
 
        if ( $this->asyncWrites && array_diff( $indexes, [ 0 ] ) && $method !== 'merge' ) {
            // Deep-clone $args to prevent misbehavior when something writes an
            // object to the BagOStuff then modifies it afterwards, e.g. T168040.
            $args = unserialize( serialize( $args ) );
        }
 
        foreach ( $indexes as $i ) {
            $cache = $this->caches[$i];
 
            if ( $i == 0 || !$this->asyncWrites ) {
                // Tier 0 store or in sync mode: write synchronously and get result
                $storeRes = $cache->proxyCall( $method, $arg0Sig, $resSig, $args, $this );
                if ( $storeRes === false ) {
                    $res = false;
                } elseif ( $res === null ) {
                    // first synchronous result
                    $res = $storeRes;
                }
            } else {
                // Secondary write in async mode: do not block this HTTP request
                ( $this->asyncHandler )(
                    function () use ( $cache, $method, $arg0Sig, $resSig, $args ) {
                        $cache->proxyCall( $method, $arg0Sig, $resSig, $args, $this );
                    }
                );
            }
        }
 
        return $res;
    }
}