[FileBackend] Improved stat caching by reducing cache salting.

[mediawiki.git] / includes / filebackend / FileBackendStore.php

<?php
/**
 * Base class for all backends using particular storage medium.
 *
 * 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 FileBackend
 * @author Aaron Schulz
 */

/**
 * @brief Base class for all backends using particular storage medium.
 *
 * This class defines the methods as abstract that subclasses must implement.
 * Outside callers should *not* use functions with "Internal" in the name.
 *
 * The FileBackend operations are implemented using basic functions
 * such as storeInternal(), copyInternal(), deleteInternal() and the like.
 * This class is also responsible for path resolution and sanitization.
 *
 * @ingroup FileBackend
 * @since 1.19
 */
abstract class FileBackendStore extends FileBackend {
        /** @var BagOStuff */
        protected $memCache;
        /** @var ProcessCacheLRU */
        protected $cheapCache; // Map of paths to small (RAM/disk) cache items
        /** @var ProcessCacheLRU */
        protected $expensiveCache; // Map of paths to large (RAM/disk) cache items

        /** @var Array Map of container names to sharding settings */
        protected $shardViaHashLevels = array(); // (container name => config array)

        protected $maxFileSize = 4294967296; // integer bytes (4GiB)

        /**
         * @see FileBackend::__construct()
         *
         * @param $config Array
         */
        public function __construct( array $config ) {
                parent::__construct( $config );
                $this->memCache       = new EmptyBagOStuff(); // disabled by default
                $this->cheapCache     = new ProcessCacheLRU( 300 );
                $this->expensiveCache = new ProcessCacheLRU( 5 );
        }

        /**
         * Get the maximum allowable file size given backend
         * medium restrictions and basic performance constraints.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * @return integer Bytes
         */
        final public function maxFileSizeInternal() {
                return $this->maxFileSize;
        }

        /**
         * Check if a file can be created at a given storage path.
         * FS backends should check if the parent directory exists and the file is writable.
         * Backends using key/value stores should check if the container exists.
         *
         * @param $storagePath string
         * @return bool
         */
        abstract public function isPathUsableInternal( $storagePath );

        /**
         * Create a file in the backend with the given contents.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - content       : the raw file contents
         *   - dst           : destination storage path
         *   - overwrite     : overwrite any file that exists at the destination
         *   - async         : Status will be returned immediately if supported.
         *                     If the status is OK, then its value field will be
         *                     set to a FileBackendStoreOpHandle object.
         *
         * @param $params Array
         * @return Status
         */
        final public function createInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                if ( strlen( $params['content'] ) > $this->maxFileSizeInternal() ) {
                        $status = Status::newFatal( 'backend-fail-maxsize',
                                $params['dst'], $this->maxFileSizeInternal() );
                } else {
                        $status = $this->doCreateInternal( $params );
                        $this->clearCache( array( $params['dst'] ) );
                        if ( !empty( $params['overwrite'] ) ) { // file possibly mutated
                                $this->deleteFileCache( $params['dst'] ); // persistent cache
                        }
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::createInternal()
         */
        abstract protected function doCreateInternal( array $params );

        /**
         * Store a file into the backend from a file on disk.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src           : source path on disk
         *   - dst           : destination storage path
         *   - overwrite     : overwrite any file that exists at the destination
         *   - async         : Status will be returned immediately if supported.
         *                     If the status is OK, then its value field will be
         *                     set to a FileBackendStoreOpHandle object.
         *
         * @param $params Array
         * @return Status
         */
        final public function storeInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                if ( filesize( $params['src'] ) > $this->maxFileSizeInternal() ) {
                        $status = Status::newFatal( 'backend-fail-maxsize',
                                $params['dst'], $this->maxFileSizeInternal() );
                } else {
                        $status = $this->doStoreInternal( $params );
                        $this->clearCache( array( $params['dst'] ) );
                        if ( !empty( $params['overwrite'] ) ) { // file possibly mutated
                                $this->deleteFileCache( $params['dst'] ); // persistent cache
                        }
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::storeInternal()
         */
        abstract protected function doStoreInternal( array $params );

        /**
         * Copy a file from one storage path to another in the backend.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src           : source storage path
         *   - dst           : destination storage path
         *   - overwrite     : overwrite any file that exists at the destination
         *   - async         : Status will be returned immediately if supported.
         *                     If the status is OK, then its value field will be
         *                     set to a FileBackendStoreOpHandle object.
         *
         * @param $params Array
         * @return Status
         */
        final public function copyInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = $this->doCopyInternal( $params );
                $this->clearCache( array( $params['dst'] ) );
                if ( !empty( $params['overwrite'] ) ) { // file possibly mutated
                        $this->deleteFileCache( $params['dst'] ); // persistent cache
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::copyInternal()
         */
        abstract protected function doCopyInternal( array $params );

        /**
         * Delete a file at the storage path.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src                 : source storage path
         *   - ignoreMissingSource : do nothing if the source file does not exist
         *   - async               : Status will be returned immediately if supported.
         *                           If the status is OK, then its value field will be
         *                           set to a FileBackendStoreOpHandle object.
         *
         * @param $params Array
         * @return Status
         */
        final public function deleteInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = $this->doDeleteInternal( $params );
                $this->clearCache( array( $params['src'] ) );
                $this->deleteFileCache( $params['src'] ); // persistent cache
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::deleteInternal()
         */
        abstract protected function doDeleteInternal( array $params );

        /**
         * Move a file from one storage path to another in the backend.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src           : source storage path
         *   - dst           : destination storage path
         *   - overwrite     : overwrite any file that exists at the destination
         *   - async         : Status will be returned immediately if supported.
         *                     If the status is OK, then its value field will be
         *                     set to a FileBackendStoreOpHandle object.
         *
         * @param $params Array
         * @return Status
         */
        final public function moveInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = $this->doMoveInternal( $params );
                $this->clearCache( array( $params['src'], $params['dst'] ) );
                $this->deleteFileCache( $params['src'] ); // persistent cache
                if ( !empty( $params['overwrite'] ) ) { // file possibly mutated
                        $this->deleteFileCache( $params['dst'] ); // persistent cache
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::moveInternal()
         * @return Status
         */
        protected function doMoveInternal( array $params ) {
                unset( $params['async'] ); // two steps, won't work here :)
                // Copy source to dest
                $status = $this->copyInternal( $params );
                if ( $status->isOK() ) {
                        // Delete source (only fails due to races or medium going down)
                        $status->merge( $this->deleteInternal( array( 'src' => $params['src'] ) ) );
                        $status->setResult( true, $status->value ); // ignore delete() errors
                }
                return $status;
        }

        /**
         * No-op file operation that does nothing.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * @param $params Array
         * @return Status
         */
        final public function nullInternal( array $params ) {
                return Status::newGood();
        }

        /**
         * @see FileBackend::concatenate()
         * @return Status
         */
        final public function concatenate( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                // Try to lock the source files for the scope of this function
                $scopeLockS = $this->getScopedFileLocks( $params['srcs'], LockManager::LOCK_UW, $status );
                if ( $status->isOK() ) {
                        // Actually do the concatenation
                        $status->merge( $this->doConcatenate( $params ) );
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::concatenate()
         * @return Status
         */
        protected function doConcatenate( array $params ) {
                $status = Status::newGood();
                $tmpPath = $params['dst']; // convenience

                // Check that the specified temp file is valid...
                wfSuppressWarnings();
                $ok = ( is_file( $tmpPath ) && !filesize( $tmpPath ) );
                wfRestoreWarnings();
                if ( !$ok ) { // not present or not empty
                        $status->fatal( 'backend-fail-opentemp', $tmpPath );
                        return $status;
                }

                // Build up the temp file using the source chunks (in order)...
                $tmpHandle = fopen( $tmpPath, 'ab' );
                if ( $tmpHandle === false ) {
                        $status->fatal( 'backend-fail-opentemp', $tmpPath );
                        return $status;
                }
                foreach ( $params['srcs'] as $virtualSource ) {
                        // Get a local FS version of the chunk
                        $tmpFile = $this->getLocalReference( array( 'src' => $virtualSource ) );
                        if ( !$tmpFile ) {
                                $status->fatal( 'backend-fail-read', $virtualSource );
                                return $status;
                        }
                        // Get a handle to the local FS version
                        $sourceHandle = fopen( $tmpFile->getPath(), 'r' );
                        if ( $sourceHandle === false ) {
                                fclose( $tmpHandle );
                                $status->fatal( 'backend-fail-read', $virtualSource );
                                return $status;
                        }
                        // Append chunk to file (pass chunk size to avoid magic quotes)
                        if ( !stream_copy_to_stream( $sourceHandle, $tmpHandle ) ) {
                                fclose( $sourceHandle );
                                fclose( $tmpHandle );
                                $status->fatal( 'backend-fail-writetemp', $tmpPath );
                                return $status;
                        }
                        fclose( $sourceHandle );
                }
                if ( !fclose( $tmpHandle ) ) {
                        $status->fatal( 'backend-fail-closetemp', $tmpPath );
                        return $status;
                }

                clearstatcache(); // temp file changed

                return $status;
        }

        /**
         * @see FileBackend::doPrepare()
         * @return Status
         */
        final protected function doPrepare( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $status = Status::newGood();
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doPrepareInternal( $fullCont, $dir, $params ) );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doPrepareInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::doPrepare()
         * @return Status
         */
        protected function doPrepareInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        /**
         * @see FileBackend::doSecure()
         * @return Status
         */
        final protected function doSecure( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doSecureInternal( $fullCont, $dir, $params ) );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doSecureInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::doSecure()
         * @return Status
         */
        protected function doSecureInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        /**
         * @see FileBackend::doPublish()
         * @return Status
         */
        final protected function doPublish( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doPublishInternal( $fullCont, $dir, $params ) );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doPublishInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::doPublish()
         * @return Status
         */
        protected function doPublishInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        /**
         * @see FileBackend::doClean()
         * @return Status
         */
        final protected function doClean( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                // Recursive: first delete all empty subdirs recursively
                if ( !empty( $params['recursive'] ) && !$this->directoriesAreVirtual() ) {
                        $subDirsRel = $this->getTopDirectoryList( array( 'dir' => $params['dir'] ) );
                        if ( $subDirsRel !== null ) { // no errors
                                foreach ( $subDirsRel as $subDirRel ) {
                                        $subDir = $params['dir'] . "/{$subDirRel}"; // full path
                                        $status->merge( $this->doClean( array( 'dir' => $subDir ) + $params ) );
                                }
                        }
                }

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                // Attempt to lock this directory...
                $filesLockEx = array( $params['dir'] );
                $scopedLockE = $this->getScopedFileLocks( $filesLockEx, LockManager::LOCK_EX, $status );
                if ( !$status->isOK() ) {
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // abort
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doCleanInternal( $fullCont, $dir, $params ) );
                        $this->deleteContainerCache( $fullCont ); // purge cache
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doCleanInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                                $this->deleteContainerCache( "{$fullCont}{$suffix}" ); // purge cache
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::doClean()
         * @return Status
         */
        protected function doCleanInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        /**
         * @see FileBackend::fileExists()
         * @return bool|null
         */
        final public function fileExists( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $stat = $this->getFileStat( $params );
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return ( $stat === null ) ? null : (bool)$stat; // null => failure
        }

        /**
         * @see FileBackend::getFileTimestamp()
         * @return bool
         */
        final public function getFileTimestamp( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $stat = $this->getFileStat( $params );
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $stat ? $stat['mtime'] : false;
        }

        /**
         * @see FileBackend::getFileSize()
         * @return bool
         */
        final public function getFileSize( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $stat = $this->getFileStat( $params );
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $stat ? $stat['size'] : false;
        }

        /**
         * @see FileBackend::getFileStat()
         * @return bool
         */
        final public function getFileStat( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return false; // invalid storage path
                }
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $latest = !empty( $params['latest'] ); // use latest data?
                if ( !$this->cheapCache->has( $path, 'stat' ) ) {
                        $this->primeFileCache( array( $path ) ); // check persistent cache
                }
                if ( $this->cheapCache->has( $path, 'stat' ) ) {
                        $stat = $this->cheapCache->get( $path, 'stat' );
                        // If we want the latest data, check that this cached
                        // value was in fact fetched with the latest available data.
                        if ( !$latest || $stat['latest'] ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                return $stat;
                        }
                }
                wfProfileIn( __METHOD__ . '-miss' );
                wfProfileIn( __METHOD__ . '-miss-' . $this->name );
                $stat = $this->doGetFileStat( $params );
                wfProfileOut( __METHOD__ . '-miss-' . $this->name );
                wfProfileOut( __METHOD__ . '-miss' );
                if ( is_array( $stat ) ) { // don't cache negatives
                        $stat['latest'] = $latest;
                        $this->cheapCache->set( $path, 'stat', $stat );
                        $this->setFileCache( $path, $stat ); // update persistent cache
                        if ( isset( $stat['sha1'] ) ) { // some backends store SHA-1 as metadata
                                $this->cheapCache->set( $path, 'sha1',
                                        array( 'hash' => $stat['sha1'], 'latest' => $latest ) );
                        }
                } else {
                        wfDebug( __METHOD__ . ": File $path does not exist.\n" );
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $stat;
        }

        /**
         * @see FileBackendStore::getFileStat()
         */
        abstract protected function doGetFileStat( array $params );

        /**
         * @see FileBackend::getFileContents()
         * @return bool|string
         */
        public function getFileContents( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $tmpFile = $this->getLocalReference( $params );
                if ( !$tmpFile ) {
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return false;
                }
                wfSuppressWarnings();
                $data = file_get_contents( $tmpFile->getPath() );
                wfRestoreWarnings();
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $data;
        }

        /**
         * @see FileBackend::getFileSha1Base36()
         * @return bool|string
         */
        final public function getFileSha1Base36( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return false; // invalid storage path
                }
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $latest = !empty( $params['latest'] ); // use latest data?
                if ( $this->cheapCache->has( $path, 'sha1' ) ) {
                        $stat = $this->cheapCache->get( $path, 'sha1' );
                        // If we want the latest data, check that this cached
                        // value was in fact fetched with the latest available data.
                        if ( !$latest || $stat['latest'] ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                return $stat['hash'];
                        }
                }
                wfProfileIn( __METHOD__ . '-miss' );
                wfProfileIn( __METHOD__ . '-miss-' . $this->name );
                $hash = $this->doGetFileSha1Base36( $params );
                wfProfileOut( __METHOD__ . '-miss-' . $this->name );
                wfProfileOut( __METHOD__ . '-miss' );
                if ( $hash ) { // don't cache negatives
                        $this->cheapCache->set( $path, 'sha1',
                                array( 'hash' => $hash, 'latest' => $latest ) );
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $hash;
        }

        /**
         * @see FileBackendStore::getFileSha1Base36()
         * @return bool|string
         */
        protected function doGetFileSha1Base36( array $params ) {
                $fsFile = $this->getLocalReference( $params );
                if ( !$fsFile ) {
                        return false;
                } else {
                        return $fsFile->getSha1Base36();
                }
        }

        /**
         * @see FileBackend::getFileProps()
         * @return Array
         */
        final public function getFileProps( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $fsFile = $this->getLocalReference( $params );
                $props = $fsFile ? $fsFile->getProps() : FSFile::placeholderProps();
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $props;
        }

        /**
         * @see FileBackend::getLocalReference()
         * @return TempFSFile|null
         */
        public function getLocalReference( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return null; // invalid storage path
                }
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $latest = !empty( $params['latest'] ); // use latest data?
                if ( $this->expensiveCache->has( $path, 'localRef' ) ) {
                        $val = $this->expensiveCache->get( $path, 'localRef' );
                        // If we want the latest data, check that this cached
                        // value was in fact fetched with the latest available data.
                        if ( !$latest || $val['latest'] ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                return $val['object'];
                        }
                }
                $tmpFile = $this->getLocalCopy( $params );
                if ( $tmpFile ) { // don't cache negatives
                        $this->expensiveCache->set( $path, 'localRef',
                                array( 'object' => $tmpFile, 'latest' => $latest ) );
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $tmpFile;
        }

        /**
         * @see FileBackend::streamFile()
         * @return Status
         */
        final public function streamFile( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                $info = $this->getFileStat( $params );
                if ( !$info ) { // let StreamFile handle the 404
                        $status->fatal( 'backend-fail-notexists', $params['src'] );
                }

                // Set output buffer and HTTP headers for stream
                $extraHeaders = isset( $params['headers'] ) ? $params['headers'] : array();
                $res = StreamFile::prepareForStream( $params['src'], $info, $extraHeaders );
                if ( $res == StreamFile::NOT_MODIFIED ) {
                        // do nothing; client cache is up to date
                } elseif ( $res == StreamFile::READY_STREAM ) {
                        wfProfileIn( __METHOD__ . '-send' );
                        wfProfileIn( __METHOD__ . '-send-' . $this->name );
                        $status = $this->doStreamFile( $params );
                        wfProfileOut( __METHOD__ . '-send-' . $this->name );
                        wfProfileOut( __METHOD__ . '-send' );
                } else {
                        $status->fatal( 'backend-fail-stream', $params['src'] );
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackendStore::streamFile()
         * @return Status
         */
        protected function doStreamFile( array $params ) {
                $status = Status::newGood();

                $fsFile = $this->getLocalReference( $params );
                if ( !$fsFile ) {
                        $status->fatal( 'backend-fail-stream', $params['src'] );
                } elseif ( !readfile( $fsFile->getPath() ) ) {
                        $status->fatal( 'backend-fail-stream', $params['src'] );
                }

                return $status;
        }

        /**
         * @see FileBackend::directoryExists()
         * @return bool|null
         */
        final public function directoryExists( array $params ) {
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        return false; // invalid storage path
                }
                if ( $shard !== null ) { // confined to a single container/shard
                        return $this->doDirectoryExists( $fullCont, $dir, $params );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
                        $res = false; // response
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $exists = $this->doDirectoryExists( "{$fullCont}{$suffix}", $dir, $params );
                                if ( $exists ) {
                                        $res = true;
                                        break; // found one!
                                } elseif ( $exists === null ) { // error?
                                        $res = null; // if we don't find anything, it is indeterminate
                                }
                        }
                        return $res;
                }
        }

        /**
         * @see FileBackendStore::directoryExists()
         *
         * @param $container string Resolved container name
         * @param $dir string Resolved path relative to container
         * @param $params Array
         * @return bool|null
         */
        abstract protected function doDirectoryExists( $container, $dir, array $params );

        /**
         * @see FileBackend::getDirectoryList()
         * @return Traversable|Array|null Returns null on failure
         */
        final public function getDirectoryList( array $params ) {
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) { // invalid storage path
                        return null;
                }
                if ( $shard !== null ) {
                        // File listing is confined to a single container/shard
                        return $this->getDirectoryListInternal( $fullCont, $dir, $params );
                } else {
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        // File listing spans multiple containers/shards
                        list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
                        return new FileBackendStoreShardDirIterator( $this,
                                $fullCont, $dir, $this->getContainerSuffixes( $shortCont ), $params );
                }
        }

        /**
         * Do not call this function from places outside FileBackend
         *
         * @see FileBackendStore::getDirectoryList()
         *
         * @param $container string Resolved container name
         * @param $dir string Resolved path relative to container
         * @param $params Array
         * @return Traversable|Array|null Returns null on failure
         */
        abstract public function getDirectoryListInternal( $container, $dir, array $params );

        /**
         * @see FileBackend::getFileList()
         * @return Traversable|Array|null Returns null on failure
         */
        final public function getFileList( array $params ) {
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) { // invalid storage path
                        return null;
                }
                if ( $shard !== null ) {
                        // File listing is confined to a single container/shard
                        return $this->getFileListInternal( $fullCont, $dir, $params );
                } else {
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        // File listing spans multiple containers/shards
                        list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
                        return new FileBackendStoreShardFileIterator( $this,
                                $fullCont, $dir, $this->getContainerSuffixes( $shortCont ), $params );
                }
        }

        /**
         * Do not call this function from places outside FileBackend
         *
         * @see FileBackendStore::getFileList()
         *
         * @param $container string Resolved container name
         * @param $dir string Resolved path relative to container
         * @param $params Array
         * @return Traversable|Array|null Returns null on failure
         */
        abstract public function getFileListInternal( $container, $dir, array $params );

        /**
         * Return a list of FileOp objects from a list of operations.
         * Do not call this function from places outside FileBackend.
         *
         * The result must have the same number of items as the input.
         * An exception is thrown if an unsupported operation is requested.
         *
         * @param $ops Array Same format as doOperations()
         * @return Array List of FileOp objects
         * @throws MWException
         */
        final public function getOperationsInternal( array $ops ) {
                $supportedOps = array(
                        'store'       => 'StoreFileOp',
                        'copy'        => 'CopyFileOp',
                        'move'        => 'MoveFileOp',
                        'delete'      => 'DeleteFileOp',
                        'create'      => 'CreateFileOp',
                        'null'        => 'NullFileOp'
                );

                $performOps = array(); // array of FileOp objects
                // Build up ordered array of FileOps...
                foreach ( $ops as $operation ) {
                        $opName = $operation['op'];
                        if ( isset( $supportedOps[$opName] ) ) {
                                $class = $supportedOps[$opName];
                                // Get params for this operation
                                $params = $operation;
                                // Append the FileOp class
                                $performOps[] = new $class( $this, $params );
                        } else {
                                throw new MWException( "Operation '$opName' is not supported." );
                        }
                }

                return $performOps;
        }

        /**
         * Get a list of storage paths to lock for a list of operations
         * Returns an array with 'sh' (shared) and 'ex' (exclusive) keys,
         * each corresponding to a list of storage paths to be locked.
         *
         * @param $performOps Array List of FileOp objects
         * @return Array ('sh' => list of paths, 'ex' => list of paths)
         */
        final public function getPathsToLockForOpsInternal( array $performOps ) {
                // Build up a list of files to lock...
                $paths = array( 'sh' => array(), 'ex' => array() );
                foreach ( $performOps as $fileOp ) {
                        $paths['sh'] = array_merge( $paths['sh'], $fileOp->storagePathsRead() );
                        $paths['ex'] = array_merge( $paths['ex'], $fileOp->storagePathsChanged() );
                }
                // Optimization: if doing an EX lock anyway, don't also set an SH one
                $paths['sh'] = array_diff( $paths['sh'], $paths['ex'] );
                // Get a shared lock on the parent directory of each path changed
                $paths['sh'] = array_merge( $paths['sh'], array_map( 'dirname', $paths['ex'] ) );

                return $paths;
        }

        /**
         * @see FileBackend::getScopedLocksForOps()
         * @return Array
         */
        public function getScopedLocksForOps( array $ops, Status $status ) {
                $paths = $this->getPathsToLockForOpsInternal( $this->getOperationsInternal( $ops ) );
                return array(
                        $this->getScopedFileLocks( $paths['sh'], LockManager::LOCK_UW, $status ),
                        $this->getScopedFileLocks( $paths['ex'], LockManager::LOCK_EX, $status )
                );
        }

        /**
         * @see FileBackend::doOperationsInternal()
         * @return Status
         */
        final protected function doOperationsInternal( array $ops, array $opts ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                // Build up a list of FileOps...
                $performOps = $this->getOperationsInternal( $ops );

                // Acquire any locks as needed...
                if ( empty( $opts['nonLocking'] ) ) {
                        // Build up a list of files to lock...
                        $paths = $this->getPathsToLockForOpsInternal( $performOps );
                        // Try to lock those files for the scope of this function...
                        $scopeLockS = $this->getScopedFileLocks( $paths['sh'], LockManager::LOCK_UW, $status );
                        $scopeLockE = $this->getScopedFileLocks( $paths['ex'], LockManager::LOCK_EX, $status );
                        if ( !$status->isOK() ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                return $status; // abort
                        }
                }

                // Clear any file cache entries (after locks acquired)
                if ( empty( $opts['preserveCache'] ) ) {
                        $this->clearCache();
                }

                // Load from the persistent file and container caches
                $this->primeFileCache( $performOps );
                $this->primeContainerCache( $performOps );

                // Actually attempt the operation batch...
                $subStatus = FileOpBatch::attempt( $performOps, $opts, $this->fileJournal );

                // Merge errors into status fields
                $status->merge( $subStatus );
                $status->success = $subStatus->success; // not done in merge()

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * @see FileBackend::doQuickOperationsInternal()
         * @return Status
         * @throws MWException
         */
        final protected function doQuickOperationsInternal( array $ops ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                $supportedOps = array( 'create', 'store', 'copy', 'move', 'delete', 'null' );
                $async = ( $this->parallelize === 'implicit' );
                $maxConcurrency = $this->concurrency; // throttle

                $statuses = array(); // array of (index => Status)
                $fileOpHandles = array(); // list of (index => handle) arrays
                $curFileOpHandles = array(); // current handle batch
                // Perform the sync-only ops and build up op handles for the async ops...
                foreach ( $ops as $index => $params ) {
                        if ( !in_array( $params['op'], $supportedOps ) ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                throw new MWException( "Operation '{$params['op']}' is not supported." );
                        }
                        $method = $params['op'] . 'Internal'; // e.g. "storeInternal"
                        $subStatus = $this->$method( array( 'async' => $async ) + $params );
                        if ( $subStatus->value instanceof FileBackendStoreOpHandle ) { // async
                                if ( count( $curFileOpHandles ) >= $maxConcurrency ) {
                                        $fileOpHandles[] = $curFileOpHandles; // push this batch
                                        $curFileOpHandles = array();
                                }
                                $curFileOpHandles[$index] = $subStatus->value; // keep index
                        } else { // error or completed
                                $statuses[$index] = $subStatus; // keep index
                        }
                }
                if ( count( $curFileOpHandles ) ) {
                        $fileOpHandles[] = $curFileOpHandles; // last batch
                }
                // Do all the async ops that can be done concurrently...
                foreach ( $fileOpHandles as $fileHandleBatch ) {
                        $statuses = $statuses + $this->executeOpHandlesInternal( $fileHandleBatch );
                }
                // Marshall and merge all the responses...
                foreach ( $statuses as $index => $subStatus ) {
                        $status->merge( $subStatus );
                        if ( $subStatus->isOK() ) {
                                $status->success[$index] = true;
                                ++$status->successCount;
                        } else {
                                $status->success[$index] = false;
                                ++$status->failCount;
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        /**
         * Execute a list of FileBackendStoreOpHandle handles in parallel.
         * The resulting Status object fields will correspond
         * to the order in which the handles where given.
         *
         * @param $handles Array List of FileBackendStoreOpHandle objects
         * @return Array Map of Status objects
         * @throws MWException
         */
        final public function executeOpHandlesInternal( array $fileOpHandles ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                foreach ( $fileOpHandles as $fileOpHandle ) {
                        if ( !( $fileOpHandle instanceof FileBackendStoreOpHandle ) ) {
                                throw new MWException( "Given a non-FileBackendStoreOpHandle object." );
                        } elseif ( $fileOpHandle->backend->getName() !== $this->getName() ) {
                                throw new MWException( "Given a FileBackendStoreOpHandle for the wrong backend." );
                        }
                }
                $res = $this->doExecuteOpHandlesInternal( $fileOpHandles );
                foreach ( $fileOpHandles as $fileOpHandle ) {
                        $fileOpHandle->closeResources();
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $res;
        }

        /**
         * @see FileBackendStore::executeOpHandlesInternal()
         * @return Array List of corresponding Status objects
         */
        protected function doExecuteOpHandlesInternal( array $fileOpHandles ) {
                foreach ( $fileOpHandles as $fileOpHandle ) { // OK if empty
                        throw new MWException( "This backend supports no asynchronous operations." );
                }
                return array();
        }

        /**
         * @see FileBackend::preloadCache()
         */
        final public function preloadCache( array $paths ) {
                $fullConts = array(); // full container names
                foreach ( $paths as $path ) {
                        list( $fullCont, $r, $s ) = $this->resolveStoragePath( $path );
                        $fullConts[] = $fullCont;
                }
                // Load from the persistent file and container caches
                $this->primeContainerCache( $fullConts );
                $this->primeFileCache( $paths );
        }

        /**
         * @see FileBackend::clearCache()
         */
        final public function clearCache( array $paths = null ) {
                if ( is_array( $paths ) ) {
                        $paths = array_map( 'FileBackend::normalizeStoragePath', $paths );
                        $paths = array_filter( $paths, 'strlen' ); // remove nulls
                }
                if ( $paths === null ) {
                        $this->cheapCache->clear();
                        $this->expensiveCache->clear();
                } else {
                        foreach ( $paths as $path ) {
                                $this->cheapCache->clear( $path );
                                $this->expensiveCache->clear( $path );
                        }
                }
                $this->doClearCache( $paths );
        }

        /**
         * Clears any additional stat caches for storage paths
         *
         * @see FileBackend::clearCache()
         *
         * @param $paths Array Storage paths (optional)
         * @return void
         */
        protected function doClearCache( array $paths = null ) {}

        /**
         * Is this a key/value store where directories are just virtual?
         * Virtual directories exists in so much as files exists that are
         * prefixed with the directory path followed by a forward slash.
         *
         * @return bool
         */
        abstract protected function directoriesAreVirtual();

        /**
         * Check if a container name is valid.
         * This checks for for length and illegal characters.
         *
         * @param $container string
         * @return bool
         */
        final protected static function isValidContainerName( $container ) {
                // This accounts for Swift and S3 restrictions while leaving room
                // for things like '.xxx' (hex shard chars) or '.seg' (segments).
                // This disallows directory separators or traversal characters.
                // Note that matching strings URL encode to the same string;
                // in Swift, the length restriction is *after* URL encoding.
                return preg_match( '/^[a-z0-9][a-z0-9-_]{0,199}$/i', $container );
        }

        /**
         * Splits a storage path into an internal container name,
         * an internal relative file name, and a container shard suffix.
         * Any shard suffix is already appended to the internal container name.
         * This also checks that the storage path is valid and within this backend.
         *
         * If the container is sharded but a suffix could not be determined,
         * this means that the path can only refer to a directory and can only
         * be scanned by looking in all the container shards.
         *
         * @param $storagePath string
         * @return Array (container, path, container suffix) or (null, null, null) if invalid
         */
        final protected function resolveStoragePath( $storagePath ) {
                list( $backend, $container, $relPath ) = self::splitStoragePath( $storagePath );
                if ( $backend === $this->name ) { // must be for this backend
                        $relPath = self::normalizeContainerPath( $relPath );
                        if ( $relPath !== null ) {
                                // Get shard for the normalized path if this container is sharded
                                $cShard = $this->getContainerShard( $container, $relPath );
                                // Validate and sanitize the relative path (backend-specific)
                                $relPath = $this->resolveContainerPath( $container, $relPath );
                                if ( $relPath !== null ) {
                                        // Prepend any wiki ID prefix to the container name
                                        $container = $this->fullContainerName( $container );
                                        if ( self::isValidContainerName( $container ) ) {
                                                // Validate and sanitize the container name (backend-specific)
                                                $container = $this->resolveContainerName( "{$container}{$cShard}" );
                                                if ( $container !== null ) {
                                                        return array( $container, $relPath, $cShard );
                                                }
                                        }
                                }
                        }
                }
                return array( null, null, null );
        }

        /**
         * Like resolveStoragePath() except null values are returned if
         * the container is sharded and the shard could not be determined.
         *
         * @see FileBackendStore::resolveStoragePath()
         *
         * @param $storagePath string
         * @return Array (container, path) or (null, null) if invalid
         */
        final protected function resolveStoragePathReal( $storagePath ) {
                list( $container, $relPath, $cShard ) = $this->resolveStoragePath( $storagePath );
                if ( $cShard !== null ) {
                        return array( $container, $relPath );
                }
                return array( null, null );
        }

        /**
         * Get the container name shard suffix for a given path.
         * Any empty suffix means the container is not sharded.
         *
         * @param $container string Container name
         * @param $relPath string Storage path relative to the container
         * @return string|null Returns null if shard could not be determined
         */
        final protected function getContainerShard( $container, $relPath ) {
                list( $levels, $base, $repeat ) = $this->getContainerHashLevels( $container );
                if ( $levels == 1 || $levels == 2 ) {
                        // Hash characters are either base 16 or 36
                        $char = ( $base == 36 ) ? '[0-9a-z]' : '[0-9a-f]';
                        // Get a regex that represents the shard portion of paths.
                        // The concatenation of the captures gives us the shard.
                        if ( $levels === 1 ) { // 16 or 36 shards per container
                                $hashDirRegex = '(' . $char . ')';
                        } else { // 256 or 1296 shards per container
                                if ( $repeat ) { // verbose hash dir format (e.g. "a/ab/abc")
                                        $hashDirRegex = $char . '/(' . $char . '{2})';
                                } else { // short hash dir format (e.g. "a/b/c")
                                        $hashDirRegex = '(' . $char . ')/(' . $char . ')';
                                }
                        }
                        // Allow certain directories to be above the hash dirs so as
                        // to work with FileRepo (e.g. "archive/a/ab" or "temp/a/ab").
                        // They must be 2+ chars to avoid any hash directory ambiguity.
                        $m = array();
                        if ( preg_match( "!^(?:[^/]{2,}/)*$hashDirRegex(?:/|$)!", $relPath, $m ) ) {
                                return '.' . implode( '', array_slice( $m, 1 ) );
                        }
                        return null; // failed to match
                }
                return ''; // no sharding
        }

        /**
         * Check if a storage path maps to a single shard.
         * Container dirs like "a", where the container shards on "x/xy",
         * can reside on several shards. Such paths are tricky to handle.
         *
         * @param $storagePath string Storage path
         * @return bool
         */
        final public function isSingleShardPathInternal( $storagePath ) {
                list( $c, $r, $shard ) = $this->resolveStoragePath( $storagePath );
                return ( $shard !== null );
        }

        /**
         * Get the sharding config for a container.
         * If greater than 0, then all file storage paths within
         * the container are required to be hashed accordingly.
         *
         * @param $container string
         * @return Array (integer levels, integer base, repeat flag) or (0, 0, false)
         */
        final protected function getContainerHashLevels( $container ) {
                if ( isset( $this->shardViaHashLevels[$container] ) ) {
                        $config = $this->shardViaHashLevels[$container];
                        $hashLevels = (int)$config['levels'];
                        if ( $hashLevels == 1 || $hashLevels == 2 ) {
                                $hashBase = (int)$config['base'];
                                if ( $hashBase == 16 || $hashBase == 36 ) {
                                        return array( $hashLevels, $hashBase, $config['repeat'] );
                                }
                        }
                }
                return array( 0, 0, false ); // no sharding
        }

        /**
         * Get a list of full container shard suffixes for a container
         *
         * @param $container string
         * @return Array
         */
        final protected function getContainerSuffixes( $container ) {
                $shards = array();
                list( $digits, $base ) = $this->getContainerHashLevels( $container );
                if ( $digits > 0 ) {
                        $numShards = pow( $base, $digits );
                        for ( $index = 0; $index < $numShards; $index++ ) {
                                $shards[] = '.' . wfBaseConvert( $index, 10, $base, $digits );
                        }
                }
                return $shards;
        }

        /**
         * Get the full container name, including the wiki ID prefix
         *
         * @param $container string
         * @return string
         */
        final protected function fullContainerName( $container ) {
                if ( $this->wikiId != '' ) {
                        return "{$this->wikiId}-$container";
                } else {
                        return $container;
                }
        }

        /**
         * Resolve a container name, checking if it's allowed by the backend.
         * This is intended for internal use, such as encoding illegal chars.
         * Subclasses can override this to be more restrictive.
         *
         * @param $container string
         * @return string|null
         */
        protected function resolveContainerName( $container ) {
                return $container;
        }

        /**
         * Resolve a relative storage path, checking if it's allowed by the backend.
         * This is intended for internal use, such as encoding illegal chars or perhaps
         * getting absolute paths (e.g. FS based backends). Note that the relative path
         * may be the empty string (e.g. the path is simply to the container).
         *
         * @param $container string Container name
         * @param $relStoragePath string Storage path relative to the container
         * @return string|null Path or null if not valid
         */
        protected function resolveContainerPath( $container, $relStoragePath ) {
                return $relStoragePath;
        }

        /**
         * Get the cache key for a container
         *
         * @param $container string Resolved container name
         * @return string
         */
        private function containerCacheKey( $container ) {
                return wfMemcKey( 'backend', $this->getName(), 'container', $container );
        }

        /**
         * Set the cached info for a container
         *
         * @param $container string Resolved container name
         * @param $val mixed Information to cache
         */
        final protected function setContainerCache( $container, $val ) {
                $this->memCache->add( $this->containerCacheKey( $container ), $val, 14*86400 );
        }

        /**
         * Delete the cached info for a container.
         * The cache key is salted for a while to prevent race conditions.
         *
         * @param $container string Resolved container name
         */
        final protected function deleteContainerCache( $container ) {
                if ( !$this->memCache->set( $this->containerCacheKey( $container ), 'PURGED', 300 ) ) {
                        trigger_error( "Unable to delete stat cache for container $container." );
                }
        }

        /**
         * Do a batch lookup from cache for container stats for all containers
         * used in a list of container names, storage paths, or FileOp objects.
         *
         * @param $items Array
         * @return void
         */
        final protected function primeContainerCache( array $items ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $paths = array(); // list of storage paths
                $contNames = array(); // (cache key => resolved container name)
                // Get all the paths/containers from the items...
                foreach ( $items as $item ) {
                        if ( $item instanceof FileOp ) {
                                $paths = array_merge( $paths, $item->storagePathsRead() );
                                $paths = array_merge( $paths, $item->storagePathsChanged() );
                        } elseif ( self::isStoragePath( $item ) ) {
                                $paths[] = $item;
                        } elseif ( is_string( $item ) ) { // full container name
                                $contNames[$this->containerCacheKey( $item )] = $item;
                        }
                }
                // Get all the corresponding cache keys for paths...
                foreach ( $paths as $path ) {
                        list( $fullCont, $r, $s ) = $this->resolveStoragePath( $path );
                        if ( $fullCont !== null ) { // valid path for this backend
                                $contNames[$this->containerCacheKey( $fullCont )] = $fullCont;
                        }
                }

                $contInfo = array(); // (resolved container name => cache value)
                // Get all cache entries for these container cache keys...
                $values = $this->memCache->getMulti( array_keys( $contNames ) );
                foreach ( $values as $cacheKey => $val ) {
                        $contInfo[$contNames[$cacheKey]] = $val;
                }

                // Populate the container process cache for the backend...
                $this->doPrimeContainerCache( array_filter( $contInfo, 'is_array' ) );

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
        }

        /**
         * Fill the backend-specific process cache given an array of
         * resolved container names and their corresponding cached info.
         * Only containers that actually exist should appear in the map.
         *
         * @param $containerInfo Array Map of resolved container names to cached info
         * @return void
         */
        protected function doPrimeContainerCache( array $containerInfo ) {}

        /**
         * Get the cache key for a file path
         *
         * @param $path string Storage path
         * @return string
         */
        private function fileCacheKey( $path ) {
                return wfMemcKey( 'backend', $this->getName(), 'file', sha1( $path ) );
        }

        /**
         * Set the cached stat info for a file path.
         * Negatives (404s) are not cached. By not caching negatives, we can skip cache
         * salting for the case when a file is created at a path were there was none before.
         *
         * @param $path string Storage path
         * @param $val mixed Information to cache
         */
        final protected function setFileCache( $path, $val ) {
                $this->memCache->add( $this->fileCacheKey( $path ), $val, 7*86400 );
        }

        /**
         * Delete the cached stat info for a file path.
         * The cache key is salted for a while to prevent race conditions.
         *
         * @param $path string Storage path
         */
        final protected function deleteFileCache( $path ) {
                if ( !$this->memCache->set( $this->fileCacheKey( $path ), 'PURGED', 300 ) ) {
                        trigger_error( "Unable to delete stat cache for file $path." );
                }
        }

        /**
         * Do a batch lookup from cache for file stats for all paths
         * used in a list of storage paths or FileOp objects.
         *
         * @param $items Array List of storage paths or FileOps
         * @return void
         */
        final protected function primeFileCache( array $items ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $paths = array(); // list of storage paths
                $pathNames = array(); // (cache key => storage path)
                // Get all the paths/containers from the items...
                foreach ( $items as $item ) {
                        if ( $item instanceof FileOp ) {
                                $paths = array_merge( $paths, $item->storagePathsRead() );
                                $paths = array_merge( $paths, $item->storagePathsChanged() );
                        } elseif ( self::isStoragePath( $item ) ) {
                                $paths[] = $item;
                        }
                }
                // Get all the corresponding cache keys for paths...
                foreach ( $paths as $path ) {
                        list( $cont, $rel, $s ) = $this->resolveStoragePath( $path );
                        if ( $rel !== null ) { // valid path for this backend
                                $pathNames[$this->fileCacheKey( $path )] = $path;
                        }
                }
                // Get all cache entries for these container cache keys...
                $values = $this->memCache->getMulti( array_keys( $pathNames ) );
                foreach ( $values as $cacheKey => $val ) {
                        if ( is_array( $val ) ) {
                                $path = $pathNames[$cacheKey];
                                $this->cheapCache->set( $path, 'stat', $val );
                                if ( isset( $val['sha1'] ) ) { // some backends store SHA-1 as metadata
                                        $this->cheapCache->set( $path, 'sha1',
                                                array( 'hash' => $val['sha1'], 'latest' => $val['latest'] ) );
                                }
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
        }
}

/**
 * FileBackendStore helper class for performing asynchronous file operations.
 *
 * For example, calling FileBackendStore::createInternal() with the "async"
 * param flag may result in a Status that contains this object as a value.
 * This class is largely backend-specific and is mostly just "magic" to be
 * passed to FileBackendStore::executeOpHandlesInternal().
 */
abstract class FileBackendStoreOpHandle {
        /** @var Array */
        public $params = array(); // params to caller functions
        /** @var FileBackendStore */
        public $backend;
        /** @var Array */
        public $resourcesToClose = array();

        public $call; // string; name that identifies the function called

        /**
         * Close all open file handles
         *
         * @return void
         */
        public function closeResources() {
                array_map( 'fclose', $this->resourcesToClose );
        }
}

/**
 * FileBackendStore helper function to handle listings that span container shards.
 * Do not use this class from places outside of FileBackendStore.
 *
 * @ingroup FileBackend
 */
abstract class FileBackendStoreShardListIterator implements Iterator {
        /** @var FileBackendStore */
        protected $backend;
        /** @var Array */
        protected $params;
        /** @var Array */
        protected $shardSuffixes;
        protected $container; // string; full container name
        protected $directory; // string; resolved relative path

        /** @var Traversable */
        protected $iter;
        protected $curShard = 0; // integer
        protected $pos = 0; // integer

        /** @var Array */
        protected $multiShardPaths = array(); // (rel path => 1)

        /**
         * @param $backend FileBackendStore
         * @param $container string Full storage container name
         * @param $dir string Storage directory relative to container
         * @param $suffixes Array List of container shard suffixes
         * @param $params Array
         */
        public function __construct(
                FileBackendStore $backend, $container, $dir, array $suffixes, array $params
        ) {
                $this->backend = $backend;
                $this->container = $container;
                $this->directory = $dir;
                $this->shardSuffixes = $suffixes;
                $this->params = $params;
        }

        /**
         * @see Iterator::key()
         * @return integer
         */
        public function key() {
                return $this->pos;
        }

        /**
         * @see Iterator::valid()
         * @return bool
         */
        public function valid() {
                if ( $this->iter instanceof Iterator ) {
                        return $this->iter->valid();
                } elseif ( is_array( $this->iter ) ) {
                        return ( current( $this->iter ) !== false ); // no paths can have this value
                }
                return false; // some failure?
        }

        /**
         * @see Iterator::current()
         * @return string|bool String or false
         */
        public function current() {
                return ( $this->iter instanceof Iterator )
                        ? $this->iter->current()
                        : current( $this->iter );
        }

        /**
         * @see Iterator::next()
         * @return void
         */
        public function next() {
                ++$this->pos;
                ( $this->iter instanceof Iterator ) ? $this->iter->next() : next( $this->iter );
                do {
                        $continue = false; // keep scanning shards?
                        $this->filterViaNext(); // filter out duplicates
                        // Find the next non-empty shard if no elements are left
                        if ( !$this->valid() ) {
                                $this->nextShardIteratorIfNotValid();
                                $continue = $this->valid(); // re-filter unless we ran out of shards
                        }
                } while ( $continue );
        }

        /**
         * @see Iterator::rewind()
         * @return void
         */
        public function rewind() {
                $this->pos = 0;
                $this->curShard = 0;
                $this->setIteratorFromCurrentShard();
                do {
                        $continue = false; // keep scanning shards?
                        $this->filterViaNext(); // filter out duplicates
                        // Find the next non-empty shard if no elements are left
                        if ( !$this->valid() ) {
                                $this->nextShardIteratorIfNotValid();
                                $continue = $this->valid(); // re-filter unless we ran out of shards
                        }
                } while ( $continue );
        }

        /**
         * Filter out duplicate items by advancing to the next ones
         */
        protected function filterViaNext() {
                while ( $this->valid() ) {
                        $rel = $this->iter->current(); // path relative to given directory
                        $path = $this->params['dir'] . "/{$rel}"; // full storage path
                        if ( $this->backend->isSingleShardPathInternal( $path ) ) {
                                break; // path is only on one shard; no issue with duplicates
                        } elseif ( isset( $this->multiShardPaths[$rel] ) ) {
                                // Don't keep listing paths that are on multiple shards
                                ( $this->iter instanceof Iterator ) ? $this->iter->next() : next( $this->iter );
                        } else {
                                $this->multiShardPaths[$rel] = 1;
                                break;
                        }
                }
        }

        /**
         * If the list iterator for this container shard is out of items,
         * then move on to the next container that has items.
         * If there are none, then it advances to the last container.
         */
        protected function nextShardIteratorIfNotValid() {
                while ( !$this->valid() && ++$this->curShard < count( $this->shardSuffixes ) ) {
                        $this->setIteratorFromCurrentShard();
                }
        }

        /**
         * Set the list iterator to that of the current container shard
         */
        protected function setIteratorFromCurrentShard() {
                $this->iter = $this->listFromShard(
                        $this->container . $this->shardSuffixes[$this->curShard],
                        $this->directory, $this->params );
                // Start loading results so that current() works
                if ( $this->iter ) {
                        ( $this->iter instanceof Iterator ) ? $this->iter->rewind() : reset( $this->iter );
                }
        }

        /**
         * Get the list for a given container shard
         *
         * @param $container string Resolved container name
         * @param $dir string Resolved path relative to container
         * @param $params Array
         * @return Traversable|Array|null
         */
        abstract protected function listFromShard( $container, $dir, array $params );
}

/**
 * Iterator for listing directories
 */
class FileBackendStoreShardDirIterator extends FileBackendStoreShardListIterator {
        /**
         * @see FileBackendStoreShardListIterator::listFromShard()
         * @return Array|null|Traversable
         */
        protected function listFromShard( $container, $dir, array $params ) {
                return $this->backend->getDirectoryListInternal( $container, $dir, $params );
        }
}

/**
 * Iterator for listing regular files
 */
class FileBackendStoreShardFileIterator extends FileBackendStoreShardListIterator {
        /**
         * @see FileBackendStoreShardListIterator::listFromShard()
         * @return Array|null|Traversable
         */
        protected function listFromShard( $container, $dir, array $params ) {
                return $this->backend->getFileListInternal( $container, $dir, $params );
        }
}