fix issue with where multiple migrations run at the same time (#377)

includes/class-activity-dispatcher.php

@@ -23,9 +23,6 @@ class Activity_Dispatcher {
 	 * Initialize the class, registering WordPress hooks.
 	 */
 	public static function init() {
-		// check if a migration is needed before sending new posts
-		Migration::maybe_migrate();
-
 		\add_action( 'activitypub_send_activity', array( self::class, 'send_activity' ), 10, 2 );
 		\add_action( 'activitypub_send_activity', array( self::class, 'send_activity_or_announce' ), 10, 2 );
 	}
@@ -39,6 +36,9 @@ class Activity_Dispatcher {
 	 * @return void
 	 */
 	public static function send_activity_or_announce( WP_Post $wp_post, $type ) {
+		// check if a migration is needed before sending new posts
+		Migration::maybe_migrate();
+
 		if ( is_user_type_disabled( 'blog' ) ) {
 			return;
 		}
@@ -93,9 +93,6 @@ class Activity_Dispatcher {
 	 * @return void
 	 */
 	public static function send_announce( WP_Post $wp_post, $type ) {
-		// check if a migration is needed before sending new posts
-		Migration::maybe_migrate();
-
 		if ( ! in_array( $type, array( 'Create', 'Update' ), true ) ) {
 			return;
 		}

includes/class-migration.php

@@ -38,6 +38,46 @@ class Migration {
 		return get_option( 'activitypub_db_version', 0 );
 	}
 
+	/**
+	 * Locks the database migration process to prevent simultaneous migrations.
+	 *
+	 * @return void
+	 */
+	public static function lock() {
+		\update_option( 'activitypub_migration_lock', \time() );
+	}
+
+	/**
+	 * Unlocks the database migration process.
+	 *
+	 * @return void
+	 */
+	public static function unlock() {
+		\delete_option( 'activitypub_migration_lock' );
+	}
+
+	/**
+	 * Whether the database migration process is locked.
+	 *
+	 * @return boolean
+	 */
+	public static function is_locked() {
+		$lock = \get_option( 'activitypub_migration_lock' );
+
+		if ( ! $lock ) {
+			return false;
+		}
+
+		$lock = (int) $lock;
+
+		if ( $lock < \time() - 1800 ) {
+			self::unlock();
+			return false;
+		}
+
+		return true;
+	}
+
 	/**
 	 * Whether the database structure is up to date.
 	 *
@@ -59,16 +99,24 @@ class Migration {
 			return;
 		}
 
+		if ( self::is_locked() ) {
+			return;
+		}
+
+		self::lock();
+
 		$version_from_db = self::get_version();
 
-		if ( version_compare( $version_from_db, '0.16.0', '<' ) ) {
+		if ( version_compare( $version_from_db, '0.17.0', '<' ) ) {
 			self::migrate_from_0_16();
 		}
-		if ( version_compare( $version_from_db, '0.17.0', '<' ) ) {
+		if ( version_compare( $version_from_db, '1.0.0', '<' ) ) {
 			self::migrate_from_0_17();
 		}
 
 		update_option( 'activitypub_db_version', self::get_target_version() );
+
+		self::unlock();
 	}
 
 	/**