Determining Whether a User Is Already Signed On, Take Three

June 28, 2002 Timothy Prickett Morgan

Hey, Ted:

When it comes to determining whether a user was signed on to more than one session, I’d do it a little differently .

I’d try to allocate the user’s message queue.

That would eliminate a data area in the mix.

— Tim

Several people wrote in with the same suggestion, Tim.

Most objected to creating the data area, saying it was unnecessary.

Here is the code to do it your way:

DCL        VAR(&FIRSTSESSN) TYPE(*LGL) VALUE('1')         
DCL        VAR(&MSGQ) TYPE(*CHAR) LEN(10)                 
DCL        VAR(&MSGQLIB) TYPE(*CHAR) LEN(10)              
                                                           
RTVUSRPRF  USRPRF(*CURRENT) MSGQ(&MSGQ) MSGQLIB(&MSGQLIB) 
ALCOBJ     OBJ((&MSGQLIB/&MSGQ *MSGQ *EXCL)) WAIT(0)      
MONMSG     MSGID(CPF1002 CPF1085) EXEC(DO)                
   CHGVAR     VAR(&FIRSTSESSN) VALUE('0')                 
ENDDO                                                     
IF         COND(&FIRSTSESSN) THEN(DO)                     
   DLCOBJ     OBJ((&MSGQLIB/&MSGQ *MSGQ *EXCL))           
ENDDO                                                     

The program attempts to allocate the message queue with an exclusive lock. This only succeeds if the user is signing on to the first session. When the user signs on to a second or subsequent session, the allocation fails, setting variable &FIRSTSESSN to false.

A reader named Mark pointed out that you should de-allocate the message queue in case other jobs need access to those messages. The de-allocation was not necessary with the original version that I presented.

— Ted

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