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hokoo · May 5, 2024 · 7fab5f8 · 7fab5f8
1 parent f0a58e8
commit 7fab5f8
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Showing 2 changed files with 54 additions and 24 deletions.
diff --git a/lib/backend/class-wp-lock-backend-db.php b/lib/backend/class-wp-lock-backend-db.php
@@ -50,41 +50,50 @@ private function get_lock_key( string $id ): string {
 		return md5( $id );
 	}
 
+	public function drop_ghosts( $lock_id ) {
+		global $wpdb;
+		$ghosts = $this->get_ghosts( $lock_id );
+
+		if ( ! empty( $ghosts ) ) {
+			$wpdb->query( "DELETE FROM {$this->get_table_name()} WHERE id IN (" . implode( ',', $ghosts ) . ")" );
+		}
+	}
+
 	/**
 	 * Ghost lock is a lock that has no corresponding process and/or connection and has no expiration time.
 	 * Search for a ghost lock for specific lock_id in the database and remove it.
 	 *
-	 * @return void
+	 * @return array List of ghost locks.
 	 */
-	public function drop_ghosts( $lock_id ) {
+	public function get_ghosts( $lock_id ): array {
 		global $wpdb;
+
 		$lock_key = $this->get_lock_key( $lock_id );
+		$locks    = $wpdb->get_results( "SELECT * FROM {$this->get_table_name()} WHERE `lock_key` = '$lock_key'", ARRAY_A );
 
-		$locks  = $wpdb->get_results( "SELECT * FROM {$this->get_table_name()} WHERE `lock_key` = '$lock_key'", ARRAY_A );
-		$ghosts = [];
-		foreach ( $locks as $lock ) {
-			if ( ! empty( $lock['expire'] ) && $lock['expire'] > microtime( true ) ) {
-				// This is an unexpired lock, keep it actual. No matter if it's a ghost or not.
-				continue;
-			}
+		// Remove unexpired locks from the list in order to keep them in DB.
+		$expired = array_filter(
+			$locks,
+			fn( $lock ) => empty( $lock['expire'] ) || $lock['expire'] <= microtime( true )
+		);
 
-			if (
-				( empty( $lock['pid'] ) && empty( $lock['cid'] ) ) ||
-				( ! empty( $lock['pid'] ) && ! file_exists( "/proc/{$lock['pid']}" ) ) ||
-				( ! empty( $lock['cid'] ) && empty(
-					$wpdb->get_var(
-						$wpdb->prepare( "SELECT id FROM information_schema.processlist WHERE id = %s", $lock['cid'] )
-					)
-					) )
-			) {
-				// This is a ghost lock, remove it.
-				$ghosts[] = $lock['id'];
-			}
+		if ( empty( $expired ) ) {
+			return [];
 		}
 
-		if ( ! empty( $ghosts ) ) {
-			$wpdb->query( "DELETE FROM {$this->get_table_name()} WHERE id IN (" . implode( ',', $ghosts ) . ")" );
-		}
+		// Get active CIDs from the database to check whether the given connections are still alive or not.
+		$active_cids = $wpdb->get_col(
+			"SELECT id FROM information_schema.processlist WHERE id IN (" .
+			implode( ',', array_column( $expired, 'cid' ) ) .
+			")"
+		);
+
+		return array_filter( $expired, function ( $lock ) use ( $active_cids ) {
+			return
+				( empty( $lock['pid'] ) && empty( $lock['cid'] ) ) ||
+				( ! empty( $lock['pid'] ) && ! file_exists( "/proc/{$lock['pid']}" ) ) ||
+				( ! empty( $lock['cid'] ) && empty( array_filter( $active_cids, fn( $cid ) => $cid == $lock['cid'] ) ) );
+		} );
 	}
 
 	/**

diff --git a/tests/lock/generic.php b/tests/lock/generic.php
@@ -237,6 +237,27 @@ public function test_concurrency_pageviews() {
 		$wpdb->suppress_errors( $suppress_errors );
 	}
 
+	public function test_ghosts( $expiration = 0 ) {
+		$resource_id = $this->generate_lock_resource_id();
+
+		$callback = new WP_Lock_Backend_Callback(
+			function( $resource_id, $expiration ) {
+				$lock_backend = new WP_Lock_Backend_DB();
+				// Born a ghost.
+				$lock_backend->acquire( $resource_id, WP_Lock::WRITE, false, $expiration );
+			},
+			[ $resource_id, $expiration ]
+		);
+
+		run_in_child( array( $callback, 'run' ) );
+		sleep( 1 + $expiration );
+		$lock_backend = new WP_Lock_Backend_DB();
+		$this->assertNotEmpty( $lock_backend->get_ghosts( $resource_id ) );
+		$this->assertTrue( $lock_backend->acquire( $resource_id, WP_Lock::WRITE, false, 0 ) XOR ! $expiration );
+		$this->assertEmpty( $lock_backend->get_ghosts( $resource_id ) );
+		$lock_backend->release( $resource_id );
+	}
+
 	public function _test_concurrency_pageviews_child( $post_id, $resource_id, $lock_backend_class) {
 		foreach ( range( 1, 100 ) as $_ ) {
 			$this->_test_concurrency_pageviews_increment_counter( $post_id, $resource_id, $lock_backend_class );