Singleton class - does this work for a User Session or for whole client ??

[Former Member]

Hello

As per my understanding the Singleton is supposed to have only one instance of class per user session.

However, I am in doubt that whether Singleton is instantiated only once for multiple user sessions. Can any one validate this idea and have a definite answer ?

If singleton is instantiated only once per client (meaning multiple user sessions) will that be one singleton class used for all sessions ?

I would greatly appreciate your help and comments..

Best regards

Vijay

Edited by: jakk on Mar 23, 2009 8:41 PM

[Former Member]

Hello

As per my understanding the Singleton is supposed to have only one instance of class per user session.

However, I am in doubt that whether Singleton is instantiated only once for multiple user sessions. Can any one validate this idea and have a definite answer ?

If singleton is instantiated only once per client (meaning multiple user sessions) will that be one singleton class used for all sessions ?

I would greatly appreciate your help and comments..

Best regards

Vijay

Edited by: jakk on Mar 23, 2009 8:41 PM

[naimesh_patel]

Your understanding is correct: "one instance of class per user session".

It would create a new object for each different user session.

Try this sample code. Put a breakpoint in the method GET_OBJECT. Run the report, stop at the breakpoint. Now, start a new Session and run the report again and you will see that it would create a new object for the new session.

*----------------------------------------------------------------------*
*       CLASS lcl_add DEFINITION
*----------------------------------------------------------------------*
CLASS lcl_add DEFINITION CREATE PRIVATE.

  PUBLIC SECTION.
    CLASS-DATA: w_time TYPE sy-uzeit.

    CLASS-METHODS:
      get_object
        EXPORTING
          eo_add TYPE REF TO lcl_add.

  PRIVATE SECTION.
    CLASS-DATA: lo_add TYPE REF TO lcl_add.

ENDCLASS.                    "lcl_add DEFINITION

*----------------------------------------------------------------------*
*       CLASS lcl_add IMPLEMENTATION
*----------------------------------------------------------------------*
CLASS lcl_add IMPLEMENTATION.

  METHOD get_object.

    IF lcl_add=>lo_add IS INITIAL.

      CREATE OBJECT lcl_add=>lo_add.

      GET TIME FIELD w_time.

    ENDIF.

    eo_add = lcl_add=>lo_add.

  ENDMETHOD.                    "get_object

ENDCLASS.                    "lcl_add IMPLEMENTATION


START-OF-SELECTION.

  DATA: o_add TYPE REF TO lcl_add.

  DATA: l_test TYPE char10.

  l_test = 'TEST'.

  CALL METHOD lcl_add=>get_object
    IMPORTING
      eo_add = o_add.

  WRITE: / lcl_add=>w_time.

  CLEAR o_add.

  CALL METHOD lcl_add=>get_object
    IMPORTING
      eo_add = o_add.

  WRITE: / lcl_add=>w_time.

Regards,

Naimesh Patel

[Former Member]

The code that you gave is for a local singleton class. What would happen for Global Singleton class that is created from SE24 ?

Best regards

Vijay

Edited by: jakk on Mar 23, 2009 9:08 PM

[naimesh_patel]

That would remain same. Try with a global class same as this example local class.

Regards,

Naimesh Patel

[matt]

>

>  I am in doubt that whether Singleton is instantiated only once for multiple user sessions. 

No, that is not the case.

[Former Member]

Thank you Matt.

I was thinking from conceptual point of view; that a Singleton (Global Class created in SE24) is instantiated only once for a user session.

Even though user is same (in case of RFC CALLS) each session (LUW) has separate Singleton intance. I hope this is correct understanding.

Best regards

Vijay.

[naimesh_patel]

Yes. It is correct "Even though user is same (in case of RFC CALLS) each session (LUW) has separate Singleton intance".

Singleton object's life time is based on the internal ABAP Session.

Like:

If you have a Singleton object for some business requirement in the Sales Order Processing, than the singleton would be active till you left the order processing.

Regards

Naimesh Patel