How we can lock No more than one user can use the table at a single time

Question

Hi Abapers,
0)  which  function modules to lock & unlock a table.
1) When you execute the program, we can check if there is any lock on this table. If yes, the user should be able to only view the table contents and not modify.
2) If there is no lock, then lock the table and go into change mode.
3) On exiting from the program, unlock the table using the function module.
4) more than one user can't modify the table just display.
Note: If there is any lock, display message saying table is locked.
Plz help me for this requirement.
Thanks
Nani

Answer 1

Hello Nani
Have a look at the lock object EMMARAE (<i>Lock MARA and MARM/MAKT exclusively</i>) in transaction SE11.
Inspect the F1 help for field <b>Lock mode</b>:
DE ENQMODE
Short Text
     Lock mode
Definition
     Defines how to synchronize table record access by several users.
The following modes exist:
     Exclusive lock
         The locked data can be read or processed by one user only. A request
         for another exclusive lock or for a shared lock is rejected.
     Shared lock
         Several users can read the same data at the same time, but as soon
         as a user edits the data, a second user can no longer access this
         data. Requests for further shared locks are accepted, even if they
         are issued by different users, but exclusive locks are rejected.
     Exclusive but not cumulative lock
         Exclusive locks can be requested by the same transaction more than
         once and handled successively, but an exclusive but not cumulative
         lock can only be requested once by a given transaction. All other
         lock requests are rejected.
If you want to lock a standard table search whether the table is used in lock objects (<i>Where-Used-List</i>). If it is a customer table you have to create your own lock object (including two function modules: one for enqueuing and the other for dequeuing).
The lock modules can be found in menu <b>GoTo -> Lock Modules</b>.
Given these lock modules the logic should be quite clear after starting the program:
1. Request lock -> if successful, continue in Change mode; -> if failed, continue in Display mode
2. Before leaving the report remove lock (note: no problem if no lock has been set in the beginning).
Regards
  Uwe