By default 4D locks a record from a table when it is loaded. Records are loaded by calling commands such as Load Record or Next Record. 4D will only load one record from a table per process. In the case where you need a process to lock multiple records in a table one solution is to use the Push Record command:
In a single process you can load multiple records and push them into the record stack. Records in the stack will remain locked until you decide to unlock them by calling Pop Record.
Another helpful tip for Push Record can be found here: