Lock Objects

[Former Member]

Hi All,

I have a table with a single key. Is there a way I can lock multiple records with a single call to the ENQUEUE function?

Regards,

Hari.

[RichHeilman]

Not that I am aware of. You lock each record with a single call to the ENQUEUE.

Regards,

RIch Heilman

[Former Member]

Hi,

You can lock them all by passing just the client and a blank key. Other than that you will have to lock each of the records in turn.

You could do this by writing a wrapper function module that accepts a table of keys, this could then loop at the table values and call the enqueue function for each entry.

Regards,

Darren

[Former Member]

No, there is no way you can achieve it. You HAVE to call ENQUE function module and pass the key value of the record you to lock.

ENQUE only locks the entry for the key passed into it.

Thanks & Regards,

Sandip Kamdar

[Former Member]

<b>A lock</b> object is a virtual link of several SAP tables which is used to synchronize simultaneous access by two users to the same set of data ( SAP lock concept).

Locks are requested and released in the programming of online transactions by calling certain function modules which are automatically generated from the definition of the lock objects. These lock objects must be explicitly created in the ABAP Dictionary.

To set locks, you must perform the following steps:

1. You must define a lock object in the ABAP Dictionary. The name of the lock object should begin with E.

2. The function modules for requesting and releasing locks which are created automatically when the lock object is activated must be linked to the programming of the relevant online transactions.

<b>Reasons for Setting Locks</b>

Suppose a travel agent want to book a flight. The customer wants to fly to a particular city with a certain airline on a certain day. The booking must only be possible if there are still free places on the flight. To avoid the possibility of overbooking, the database entry corresponding to the flight must be locked against access from other transactions. This ensures that one user can find out the number of free places, make the booking, and change the number of free places without the data being changed in the meantime by another transaction.

<b>Lock Mechanisms in the Database System</b>

The database system automatically sets database locks when it receives change statements (INSERT, UPDATE, MODIFY, DELETE) from a program. Database locks are physical locks on the database entries affected by these statements. You can only set a lock for an existing database entry, since the lock mechanism uses a lock flag in the entry. These flags are automatically deleted in each database commit. This means that database locks can never be set for longer than a single database LUW; in other words, a single dialog step in an R/3 application program.

Physical locks in the database system are therefore insufficient for the requirements of an R/3 transaction. Locks in the R/3 System must remain set for the duration of a whole SAP LUW, that is, over several dialog steps. They must also be capable of being handled by different work processes and even different application servers. Consequently, each lock must apply on all servers in that R/3 System.

<b>SAP Locks</b>

To complement the SAP LUW concept, in which bundled database changes are made in a single database LUW, the R/3 System also contains a lock mechanism, fully independent of database locks, that allows you to set a lock that spans several dialog steps. These locks are known as SAP locks.

The SAP lock concept is based on lock objects. Lock objects allow you to set an SAP lock for an entire application object. An application object consists of one or more entries in a database table, or entries from more than one database table that are linked using foreign key relationships.

Before you can set an SAP lock in an ABAP program, you must first create a lock object in the ABAP Dictionary. A lock object definition contains the database tables and their key fields on the basis of which you want to set a lock. When you create a lock object, the system automatically generates two function modules with the names <b>ENQUEUE_<lock object name></b> and <b>DEQUEUE_<lock object name></b> . You can then set and release SAP locks in your ABAP program by calling these function modules in a <b>CALL FUNCTION</b> statement.

<b>Lock Types</b>

<b>There are two types of lock in the R/3 System:</b>

<b>Shared lock</b>

Shared locks (or read locks) allow you to prevent data from being changed while you are reading it. They prevent other programs from setting an exclusive lock (write lock) to change the object. It does not, however, prevent other programs from setting further read locks.

<b>Exclusive lock</b>

Exclusive locks (or write locks) allow you to prevent data from being changed while you are changing it yourself. An exclusive lock, as its name suggests, locks an application object for exclusive use by the program that sets it. No other program can then set either a shared lock or an exclusive lock for the same application object.

<b>example</b> uses the lock object <b>ESFLIGHT</b> and its function modules <b>ENQUEUE_ESFLIGHT</b> and <b>DEQUEUE_ESFLIGHT</b> to lock and unlock the object.

For more information about creating lock objects and the corresponding function modules, refer to the Lock objects section of the ABAP Dictionary documentation.

The PAI processing for screen 100 in this transaction processes the user input and prepares for the requested action (Change or Display). If the user chooses Change, the program locks the relevant database object by calling the corresponding ENQUEUE function.

MODULE USER_COMMAND_0100 INPUT.
  CASE OK_CODE.
    WHEN 'SHOW'....
    WHEN 'CHNG'.
* <...Authority-check and other code...>
      CALL FUNCTION 'ENQUEUE_ESFLIGHT'
EXPORTING
MANDT = SY-MANDT
CARRID = SPFLI-CARRID
CONNID = SPFLI-CONNID
EXCEPTIONS
FOREIGN_LOCK = 1
SYSTEM_FAILURE = 2
OTHERS = 3.
IF SY-SUBRC NE 0.
MESSAGE ID SY-MSGID
TYPE 'E'
NUMBER SY-MSGNO
WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
      ENDIF.

...

The ENQUEUE function module can trigger the following exceptions:

FOREIGN_LOCK determines whether a conflicting lock already exists. The system variable SY-MSGV1 contains the name of the user that owns the lock.

The SYSTEM_FAILURE exception is triggered if the enqueue server is unable to set the lock for technical reasons.

At the end of a transaction, the locks are released automatically. However, there are exceptions if you have called update routines within the transaction. You can release a lock explicitly by calling the corresponding DEQUEUE module. As the programmer, you must decide for yourself the point at which it makes most sense to release the locks (for example, to make the data available to other transactions).

If you need to use the DEQUEUE function module call several times in a program, it makes good sense to write it in a subroutine, which you then call as required.

The subroutine UNLOCK_FLIGHT calls the DEQUEUE function module for the lock object ESFLIGHT:

FORM UNLOCK_FLIGHT.
     CALL FUNCTION 'DEQUEUE_ESFLIGHT'
          EXPORTING
              MANDT     = SY-MANDT
              CARRID    = SPFLI-CARRID
              CONNID    = SPFLI-CONNID
          EXCEPTIONS
              OTHERS    = 1.
     SET SCREEN 100.
ENDFORM.

You might use this for the BACK and EXIT functions in a PAI module for screen 200 in this example transaction. In the program, the system checks whether the user leaves the screen without having saved his or her changes. If so, the PROMPT_AND_SAVE routine sends a reminder, and gives the user the opportunity to save the changes. The flight can be unlocked by calling the UNLOCK_FLIGHT subroutine.

MODULE USER_COMMAND_0200 INPUT.
  CASE OK_CODE.
    WHEN 'SAVE'....
    WHEN 'EXIT'.
      CLEAR OK_CODE.
      IF OLD_SPFLI NE SPFLI.
         PERFORM PROMPT_AND_SAVE.
      ENDIF.
      PERFORM UNLOCK_FLIGHT.
      LEAVE TO SCREEN 0.
    WHEN 'BACK'....

<b>Another Example :</b>

please see this link with Screen shot .....

<a href="http://">http://help.sap.com/saphelp_nw04/helpdata/en/cf/21eea5446011d189700000e8322d00/frameset.htm</a>

reward points if it is usefull ......

Girish