Add a method to lock a table

lib/private/AppFramework/Db/Db.php

@@ -29,6 +29,7 @@ namespace OC\AppFramework\Db;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\IDb;
 use OCP\IDBConnection;
+use OCP\PreConditionNotMetException;
 
 /**
  * @deprecated use IDBConnection directly, will be removed in ownCloud 10
@@ -157,12 +158,26 @@ class Db implements IDb {
 	 * @param array $updatePreconditionValues ensure values match preconditions (column name => value)
 	 * @return int number of new rows
 	 * @throws \Doctrine\DBAL\DBALException
-	 * @throws PreconditionNotMetException
+	 * @throws PreConditionNotMetException
 	 */
 	public function setValues($table, array $keys, array $values, array $updatePreconditionValues = []) {
 		return $this->connection->setValues($table, $keys, $values, $updatePreconditionValues);
 	}
 
+	/**
+	 * @inheritdoc
+	 */
+	public function lockTable($tableName) {
+		$this->connection->lockTable($tableName);
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function unlockTable() {
+		$this->connection->unlockTable();
+	}
+
 	/**
 	 * Start a transaction
 	 */

lib/private/DB/Adapter.php

@@ -57,6 +57,26 @@ class Adapter {
 		return $statement;
 	}
 
+	/**
+	 * Create an exclusive read+write lock on a table
+	 *
+	 * @param string $tableName
+	 * @since 9.1.0
+	 */
+	public function lockTable($tableName) {
+		$this->conn->beginTransaction();
+		$this->conn->executeUpdate('LOCK TABLE `' .$tableName . '` IN EXCLUSIVE MODE');
+	}
+
+	/**
+	 * Release a previous acquired lock again
+	 *
+	 * @since 9.1.0
+	 */
+	public function unlockTable() {
+		$this->conn->commit();
+	}
+
 	/**
 	 * Insert a row if the matching row does not exists.
 	 *

lib/private/DB/AdapterMySQL.php

@@ -24,6 +24,18 @@
 namespace OC\DB;
 
 class AdapterMySQL extends Adapter {
+
+	/**
+	 * @param string $tableName
+	 */
+	public function lockTable($tableName) {
+		$this->conn->executeUpdate('LOCK TABLES `' .$tableName . '` WRITE');
+	}
+
+	public function unlockTable() {
+		$this->conn->executeUpdate('UNLOCK TABLES');
+	}
+
 	public function fixupStatement($statement) {
 		$statement = str_replace(' ILIKE ', ' COLLATE utf8_general_ci LIKE ', $statement);
 		return $statement;

lib/private/DB/AdapterSqlite.php

@@ -27,6 +27,18 @@
 namespace OC\DB;
 
 class AdapterSqlite extends Adapter {
+
+	/**
+	 * @param string $tableName
+	 */
+	public function lockTable($tableName) {
+		$this->conn->executeUpdate('BEGIN EXCLUSIVE TRANSACTION');
+	}
+
+	public function unlockTable() {
+		$this->conn->executeUpdate('COMMIT TRANSACTION');
+	}
+
 	public function fixupStatement($statement) {
 		$statement = preg_replace('( I?LIKE \?)', '$0 ESCAPE \'\\\'', $statement);
 		$statement = preg_replace('/`(\w+)` ILIKE \?/', 'LOWER($1) LIKE LOWER(?)', $statement);

lib/private/DB/Connection.php

@@ -25,6 +25,7 @@
  */
 
 namespace OC\DB;
+
 use Doctrine\DBAL\DBALException;
 use Doctrine\DBAL\Driver;
 use Doctrine\DBAL\Configuration;
@@ -46,6 +47,8 @@ class Connection extends \Doctrine\DBAL\Connection implements IDBConnection {
 	 */
 	protected $adapter;
 
+	protected $lockedTable = null;
+
 	public function connect() {
 		try {
 			return parent::connect();
@@ -281,7 +284,7 @@ class Connection extends \Doctrine\DBAL\Connection implements IDBConnection {
 			foreach ($values as $name => $value) {
 				$updateQb->set($name, $updateQb->createNamedParameter($value, $this->getType($value)));
 			}
-			$where = $updateQb->expr()->andx();
+			$where = $updateQb->expr()->andX();
 			$whereValues = array_merge($keys, $updatePreconditionValues);
 			foreach ($whereValues as $name => $value) {
 				$where->add($updateQb->expr()->eq(
@@ -301,6 +304,33 @@ class Connection extends \Doctrine\DBAL\Connection implements IDBConnection {
 		}
 	}
 
+	/**
+	 * Create an exclusive read+write lock on a table
+	 *
+	 * @param string $tableName
+	 * @throws \BadMethodCallException When trying to acquire a second lock
+	 * @since 9.1.0
+	 */
+	public function lockTable($tableName) {
+		if ($this->lockedTable !== null) {
+			throw new \BadMethodCallException('Can not lock a new table until the previous lock is released.');
+		}
+
+		$tableName = $this->tablePrefix . $tableName;
+		$this->lockedTable = $tableName;
+		$this->adapter->lockTable($tableName);
+	}
+
+	/**
+	 * Release a previous acquired lock again
+	 *
+	 * @since 9.1.0
+	 */
+	public function unlockTable() {
+		$this->adapter->unlockTable();
+		$this->lockedTable = null;
+	}
+
 	/**
 	 * returns the error code and message as a string for logging
 	 * works with DoctrineException

lib/public/IDBConnection.php

@@ -124,6 +124,25 @@ interface IDBConnection {
 	 */
 	public function setValues($table, array $keys, array $values, array $updatePreconditionValues = []);
 
+	/**
+	 * Create an exclusive read+write lock on a table
+	 *
+	 * Important Note: Due to the nature how locks work on different DBs, it is
+	 * only possible to lock one table at a time. You should also NOT start a
+	 * transaction while holding a lock.
+	 *
+	 * @param string $tableName
+	 * @since 9.1.0
+	 */
+	public function lockTable($tableName);
+
+	/**
+	 * Release a previous acquired lock again
+	 *
+	 * @since 9.1.0
+	 */
+	public function unlockTable();
+
 	/**
 	 * Start a transaction
 	 * @since 6.0.0