Avoid race conditions when configuring the SQLite database

Author: JanJakes

Diff for: wp-includes/sqlite-ast/class-wp-sqlite-configurator.php

@@ -57,11 +57,20 @@ public function __construct(
 	 * driver version, and if it is not, it will configure the database.
 	 */
 	public function ensure_database_configured(): void {
-		$version    = SQLITE_DRIVER_VERSION;
-		$db_version = $this->driver->get_saved_driver_version();
-		if ( version_compare( $version, $db_version ) > 0 ) {
-			$this->configure_database();
+		// Use an EXCLUSIVE transaction to prevent multiple connections
+		// from attempting to configure the database at the same time.
+		$this->driver->execute_sqlite_query( 'BEGIN EXCLUSIVE TRANSACTION' );
+		try {
+			$version    = SQLITE_DRIVER_VERSION;
+			$db_version = $this->driver->get_saved_driver_version();
+			if ( version_compare( $version, $db_version ) > 0 ) {
+				$this->run_database_configuration();
+			}
+		} catch ( Throwable $e ) {
+			$this->driver->execute_sqlite_query( 'ROLLBACK' );
+			throw $e;
 		}
+		$this->driver->execute_sqlite_query( 'COMMIT' );
 	}
 
 	/**
@@ -73,6 +82,25 @@ public function ensure_database_configured(): void {
 	 * SQLite driver version and attempt to repair any configuration corruption.
 	 */
 	public function configure_database(): void {
+		// Use an EXCLUSIVE transaction to prevent multiple connections
+		// from attempting to configure the database at the same time.
+		$this->driver->execute_sqlite_query( 'BEGIN EXCLUSIVE TRANSACTION' );
+		try {
+			$this->run_database_configuration();
+		} catch ( Throwable $e ) {
+			$this->driver->execute_sqlite_query( 'ROLLBACK' );
+			throw $e;
+		}
+		$this->driver->execute_sqlite_query( 'COMMIT' );
+	}
+
+	/**
+	 * Run the SQLite database configuration.
+	 *
+	 * This method executes the database configuration steps, ensuring that all
+	 * tables required for MySQL emulation in SQLite are created and populated.
+	 */
+	private function run_database_configuration(): void {
 		$this->ensure_global_variables_table();
 		$this->information_schema_builder->ensure_information_schema_tables();
 		$this->information_schema_reconstructor->ensure_correct_information_schema();