Editing Object REXX (section)

=== Multi-threading ===
Conceptually, ooRexx provides object-based [[Concurrency (computer science)|concurrency]], according to which objects have independent resources to execute methods and can communicate with each other using the messaging paradigm. Several objects can be active at the same time and exchange messages for [[Synchronization (computer science)|synchronization]].<ref name=":2" /> Concurrency can be achieved with the <code>REPLY</code> keyword instruction, which causes an early return from a method while its remainder continues to execute in a new thread. Alternatively, the keyword instruction <code>GUARD</code> can be used to mark a method as unprotected so that it can be executed together with other methods of the same class. Finally, using the <code>START</code> method (Object or Message class) causes the recipient to process the received message in a separate thread, thus also enabling concurrency.<ref name=":2" />