Avoid races in MessageCache::replace()
Do the process cache update immediately (as before) but push the shared cache updates to a deferred update. This update will thus start with a clear transaction snapshot, so it can acquire the lock before the first SELECT as is proper. Also added some missing method visibilities. Bug: T144952 Change-Id: I462554b300d4688b09ab80cd1bb8a4340ffaa786
This commit is contained in:
Aaron Schulz
Krinkle
parent
decb55fdf9
commit
c962b48056
2 changed files with 97 additions and 53 deletions
119
includes/cache/MessageCache.php
vendored
119
includes/cache/MessageCache.php
vendored
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@ -444,7 +444,7 @@ class MessageCache {
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* @param integer $mode Use MessageCache::FOR_UPDATE to skip process cache
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* @return array Loaded messages for storing in caches
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*/
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function loadFromDB( $code, $mode = null ) {
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protected function loadFromDB( $code, $mode = null ) {
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global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
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$dbr = wfGetDB( ( $mode == self::FOR_UPDATE ) ? DB_MASTER : DB_REPLICA );
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@ -518,7 +518,7 @@ class MessageCache {
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wfDebugLog(
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'MessageCache',
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__METHOD__
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. ": failed to load message page text for {$row->page_title} ($code)"
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. ": failed to load message page text for {$row->page_title} ($code)"
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);
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} else {
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$entry = ' ' . $text;
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@ -541,11 +541,11 @@ class MessageCache {
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/**
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* Updates cache as necessary when message page is changed
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*
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* @param string|bool $title Name of the page changed (false if deleted)
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* @param string $title Message cache key with initial uppercase letter.
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* @param string|bool $text New contents of the page (false if deleted)
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*/
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public function replace( $title, $text ) {
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global $wgMaxMsgCacheEntrySize, $wgContLang, $wgLanguageCode;
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global $wgLanguageCode;
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if ( $this->mDisable ) {
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return;
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@ -557,63 +557,75 @@ class MessageCache {
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return;
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}
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// Note that if the cache is volatile, load() may trigger a DB fetch.
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// In that case we reenter/reuse the existing cache key lock to avoid
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// a self-deadlock. This is safe as no reads happen *directly* in this
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// method between getReentrantScopedLock() and load() below. There is
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// no risk of data "changing under our feet" for replace().
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$scopedLock = $this->getReentrantScopedLock( wfMemcKey( 'messages', $code ) );
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// Load the messages from the master DB to avoid race conditions
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$this->load( $code, self::FOR_UPDATE );
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// Load the new value into the process cache...
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// (a) Update the process cache with the new message text
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if ( $text === false ) {
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// Page deleted
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$this->mCache[$code][$title] = '!NONEXISTENT';
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} elseif ( strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
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$this->mCache[$code][$title] = '!TOO BIG';
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// Pre-fill the individual key cache with the known latest message text
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$key = $this->wanCache->makeKey( 'messages-big', $this->mCache[$code]['HASH'], $title );
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$this->wanCache->set( $key, " $text", $this->mExpiry );
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} else {
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// Ignore $wgMaxMsgCacheEntrySize so the process cache is up to date
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$this->mCache[$code][$title] = ' ' . $text;
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}
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// Mark this cache as definitely being "latest" (non-volatile) so
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// load() calls do not try to refresh the cache with replica DB data
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$this->mCache[$code]['LATEST'] = time();
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// Update caches if the lock was acquired
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if ( $scopedLock ) {
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$this->saveToCaches( $this->mCache[$code], 'all', $code );
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} else {
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LoggerFactory::getInstance( 'MessageCache' )->error(
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__METHOD__ . ': could not acquire lock to update {title} ({code})',
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[ 'title' => $title, 'code' => $code ] );
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}
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// (b) Update the shared caches in a deferred update with a fresh DB snapshot
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DeferredUpdates::addCallableUpdate(
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function () use ( $title, $msg, $code ) {
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global $wgContLang, $wgMaxMsgCacheEntrySize;
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// Allow one caller at a time to avoid race conditions
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$scopedLock = $this->getReentrantScopedLock( wfMemcKey( 'messages', $code ) );
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if ( !$scopedLock ) {
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LoggerFactory::getInstance( 'MessageCache' )->error(
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__METHOD__ . ': could not acquire lock to update {title} ({code})',
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[ 'title' => $title, 'code' => $code ] );
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return;
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}
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// Load the messages from the master DB to avoid race conditions
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$this->loadFromDB( $code, self::FOR_UPDATE );
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// Load the process cache values and set the per-title cache keys
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$page = WikiPage::factory( Title::makeTitle( NS_MEDIAWIKI, $title ) );
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$page->loadPageData( $page::READ_LATEST );
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$text = $this->getMessageTextFromContent( $page->getContent() );
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// Check if an individual cache key should exist and update cache accordingly
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$titleKey = $this->wanCache->makeKey(
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'messages-big', $this->mCache[$code]['HASH'], $title );
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if ( is_string( $text ) && strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
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$this->wanCache->set( $titleKey, ' ' . $text, $this->mExpiry );
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}
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// Mark this cache as definitely being "latest" (non-volatile) so
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// load() calls do try to refresh the cache with replica DB data
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$this->mCache[$code]['LATEST'] = time();
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// Pre-emptively update the local datacenter cache so things like edit filter and
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// blacklist changes are reflect immediately, as these often use MediaWiki: pages.
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// The datacenter handling replace() calls should be the same one handling edits
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// as they require HTTP POST.
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$this->saveToCaches( $this->mCache[$code], 'all', $code );
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// Release the lock now that the cache is saved
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ScopedCallback::consume( $scopedLock );
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ScopedCallback::consume( $scopedLock );
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// Relay the purge. Touching this check key expires cache contents
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// and local cache (APC) validation hash across all datacenters.
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$this->wanCache->touchCheckKey( wfMemcKey( 'messages', $code ) );
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// Relay the purge. Touching this check key expires cache contents
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// and local cache (APC) validation hash across all datacenters.
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$this->wanCache->touchCheckKey( wfMemcKey( 'messages', $code ) );
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// Also delete cached sidebar... just in case it is affected
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// @TODO: shouldn't this be $code === $wgLanguageCode?
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if ( $code === 'en' ) {
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// Purge all language sidebars, e.g. on ?action=purge to the sidebar messages
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$codes = array_keys( Language::fetchLanguageNames() );
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} else {
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// Purge only the sidebar for this language
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$codes = [ $code ];
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}
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foreach ( $codes as $code ) {
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$this->wanCache->delete( wfMemcKey( 'sidebar', $code ) );
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}
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// Also delete cached sidebar... just in case it is affected
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$codes = [ $code ];
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if ( $code === 'en' ) {
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// Delete all sidebars, like for example on action=purge on the
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// sidebar messages
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$codes = array_keys( Language::fetchLanguageNames() );
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}
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// Purge the message in the message blob store
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$resourceloader = RequestContext::getMain()->getOutput()->getResourceLoader();
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$blobStore = $resourceloader->getMessageBlobStore();
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$blobStore->updateMessage( $wgContLang->lcfirst( $msg ) );
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foreach ( $codes as $code ) {
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$sidebarKey = wfMemcKey( 'sidebar', $code );
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$this->wanCache->delete( $sidebarKey );
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}
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// Update the message in the message blob store
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$resourceloader = RequestContext::getMain()->getOutput()->getResourceLoader();
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$blobStore = $resourceloader->getMessageBlobStore();
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$blobStore->updateMessage( $wgContLang->lcfirst( $msg ) );
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Hooks::run( 'MessageCacheReplace', [ $title, $text ] );
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Hooks::run( 'MessageCacheReplace', [ $title, $text ] );
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},
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DeferredUpdates::PRESEND
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);
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}
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/**
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@ -845,7 +857,7 @@ class MessageCache {
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$alreadyTried = [];
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// First try the requested language.
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// First try the requested language.
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$message = $this->getMessageForLang( $lang, $lckey, $useDB, $alreadyTried );
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if ( $message !== false ) {
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return $message;
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@ -950,6 +962,7 @@ class MessageCache {
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*/
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public function getMsgFromNamespace( $title, $code ) {
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$this->load( $code );
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if ( isset( $this->mCache[$code][$title] ) ) {
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$entry = $this->mCache[$code][$title];
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if ( substr( $entry, 0, 1 ) === ' ' ) {
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@ -99,6 +99,37 @@ class MessageCacheTest extends MediaWikiLangTestCase {
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];
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}
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public function testReplaceMsg() {
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global $wgContLang;
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$messageCache = MessageCache::singleton();
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$message = 'go';
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$uckey = $wgContLang->ucfirst( $message );
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$oldText = $messageCache->get( $message ); // "Ausführen"
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$dbw = wfGetDB( DB_MASTER );
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$dbw->startAtomic( __METHOD__ ); // simulate request and block deferred updates
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$messageCache->replace( $uckey, 'Allez!' );
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$this->assertEquals( 'Allez!',
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$messageCache->getMsgFromNamespace( $uckey, 'de' ),
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'Updates are reflected in-process immediately' );
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$this->assertEquals( 'Allez!',
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$messageCache->get( $message ),
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'Updates are reflected in-process immediately' );
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$this->makePage( 'Go', 'de', 'Race!' );
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$dbw->endAtomic( __METHOD__ );
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$this->assertEquals( 0,
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DeferredUpdates::pendingUpdatesCount(),
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'Post-commit deferred update triggers a run of all updates' );
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$this->assertEquals( 'Race!', $messageCache->get( $message ), 'Correct final contents' );
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$this->makePage( 'Go', 'de', $oldText );
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$messageCache->replace( $uckey, $oldText ); // deferred update runs immediately
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$this->assertEquals( $oldText, $messageCache->get( $message ), 'Content restored' );
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}
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/**
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* There's a fallback case where the message key is given as fully qualified -- this
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* should ignore the passed $lang and use the language from the key
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