how to lock objects with an oData Service

Hi,

Example:

Somebody should change an order on his mobile device. How can i lock them for other users?

(best case, linked to the session time btw. How can i show all valid sessions?)

Problem:

The standard lock concept of SAP is based on a LUW concept...  I can create a lock at the get_entity method, but this look is auto-released, after processing the request. Or in other words, the look is not bounded on the session time.....

Question:
How can I create a lock between a read and an update request,?

I found some documentation about the sross-system lock, but I could not find any ABAP code example.

Thanks and Regards

Beny