Check lock-status of record without locking it.

[Marc Vanzegbroeck]

Hi,

How can I check of a reckord is locked by an other user without locking it (so not use rlock())
I already tested it with DbRecordInfo(2), but this return .f. even when it's locked

Marc

[Marc Vanzegbroeck]

Hi,

I also tested it with DbRLockList(), but this function returns an empty array, even when someone has locked a record.
Does it only return the records locked by the lockal PC , and not the records locked by someone else?

Marc

[driessen]

Hello Mark,

I have written my own locking system which is working very well.

First of all, I have 3 fields in every DBF-file I use :

PRDURE D 20
PRLINE N 5
CTRAFK C 3

To lock my records, I use this code :

Code: Select all  Expand view

FUNCTION RecLock(RLWijze,RLProc,RLLine,RLWaitSec,RLTaal,RLShow,RLAltijd,RLUser)

   LOCAL lForever
   LOCAL nWait
   LOCAL lRedo      := .T.
   LOCAL nOrde      := INDEXORD()

   DEFAULT(RLWijze,1)
   DEFAULT(RLWaitSec,0.1)
   DEFAULT(RLTaal,"N")
   DEFAULT(RLShow,.T.)
   DEFAULT(RLAltijd,.F.)

   IF RLWijze = 2
      DEFAULT(RLUser,xLockUser)
   ENDIF

   SET ORDER TO 0

   lForever=(RLWaitSec==0)

   DO WHILE lRedo
      nWait=RLWaitSec*2
      DO WHILE lForever .OR. nWait>0
         IF RLOCK()
            IF !NETERR()
               IF RLWijze = 1
                  SET ORDER TO nOrde
                  RETURN(.T.)
               ELSE
                  IF RLAltijd .OR. EMPTY(&(ALIAS()+"->CTRAFK")) .OR. UPPER(ALLTRIM(&(ALIAS()+"->CTRAFK"))) = UPPER(ALLTRIM(RLUser))
                     &(ALIAS()+"->CTRAFK") := RLUser
                     &(ALIAS()+"->PRDURE") := RLProc
                     &(ALIAS()+"->PRLINE") := RLLine
                     IF xCommit
                        COMMIT
                     ELSE
                        UNLOCK
                        RLOCK()
                     ENDIF
                     SET ORDER TO nOrde
                     RETURN(.T.)
                  ENDIF
               ENDIF
            ENDIF
         ENDIF
         INKEY(.5)
         nWait--
      ENDDO
      IF RLShow
         lRedo := MsgYesNo("De gegevens welke U wenst aan te passen,"+CHR(13)+;
                           "zijn in gebruik met de volgende parameters :"+CHR(13)+;
                            CHR(13)+;
                            "Betreft de volgende gegevens :"+CHR(13)+;
                            CHR(13)+;
                            "  - Bestand : "+ALIAS()+CHR(13)+;
                            "  - Record nr. : "+ALLTRIM(STR(RECNO()))+CHR(13)+;
                            CHR(13)+;
                            "U wilt deze gegevens in gebruik nemen :"+CHR(13)+;
                            CHR(13)+;
                            IF(RLWijze=2,"  - Gebruiker : "+ALLTRIM(RLUser)+CHR(13),"")+;
                            "  - Procedure : "+RLProc+CHR(13)+;
                            "  - Lijn nr. : "+ALLTRIM(STR(RLLine))+CHR(13)+;
                            CHR(13)+;
                            "Deze gegevens worden gebruikt door :"+CHR(13)+;
                            CHR(13)+;
                            IF(EMPTY(&(ALIAS()+"->CTRAFK")),"- Softwarelock","  - Gebruiker : "+ALLTRIM(&(ALIAS()+"->CTRAFK"))+CHR(13)+;
                                                                                                IF(!EMPTY(&(ALIAS()+"->PRDURE")),"  - Procedure : "+ALLTRIM(&(ALIAS()+"->PRDURE"     ))+CHR(13),"")+;
                                                                                                IF(&(ALIAS()+"->PRLINE")<>0     ,"  - Lijn nr. : " +ALLTRIM(STR(&(ALIAS()+"->PRLINE")))+CHR(13),""))+;
                            CHR(13)+;
                            "Wenst U opnieuw te proberen ?",;
                            "Kies "+CHR(34)+"JA"+CHR(34)+" of "+CHR(34)+"NEE"+CHR(34))
      ELSE
         lRedo := .F.
      ENDIF
      IF !lRedo .AND. RLWijze = 2 ; UNLOCK ; ENDIF
   ENDDO

   SET ORDER TO nOrde

RETURN(.F.)
 

To unlock my record, I use this code :

Code: Select all  Expand view

PROCEDURE RecUnLock(RLWijze,RLProc,RLLine,RLUser)

   DEFAULT(RLWijze,1)

   IF RlWijze = 2
      DEFAULT(RLUser,xLockUser)
   ENDIF

   IF RLWijze = 1
      IF xCommit ; COMMIT ; ENDIF
      UNLOCK
   ELSE
      IF !EMPTY(&(ALIAS()+"->CTRAFK")) .AND. UPPER(ALLTRIM(&(ALIAS()+"->CTRAFK"))) = UPPER(ALLTRIM(RLUser))
         IF RecLockJuda(1,PROCNAME(),PROCLINE(),2,TaalCode)
            &(ALIAS()+"->CTRAFK") := SPACE( 3)
            &(ALIAS()+"->PRDURE") := SPACE(20)
            &(ALIAS()+"->PRLINE") := 0
         ENDIF
         IF xCommit ; COMMIT ; ENDIF
         UNLOCK
      ENDIF
   ENDIF

RETURN
 

To lock my record, all I do is :

Code: Select all  Expand view

RecLock(2,PROCNAME(),PROCLINE(),5,TaalCode)

And to unlock :

Code: Select all  Expand view

RecUnLock(2,PROCNAME(),PROCLINE())

I always see who has locked a record and where he has locked it.
It's always a very intereting something for debugging.

If any questions, don't hesitate to ask.

Good luck.

[James Bott]

Marc,

If you are using TDatabase it has a method isLocked(). If you are not using TDatabase, then use the code in the islocked() method.

I highly recommend using a database class. For more about using database classes see my website at http://www.gointellitech.com

James

[Marc Vanzegbroeck]

Michel,

Thanks for the example. Before, I was using something simular, but there was a problem when for some reason the program ended not normal (error or crash PC). The record was always locked for the other users.
Then the program should be restarted on that PC for unlocking the record. Sometime he user didn' restard the program, with the result that nobody can access that record anymore. I was thinking for a method tho theck that the PC that has locked the record is still running the program, but I did'n find a good solution for that yet. A was thinking for using a timer a always update a record. If the record isn't updated anymore, the program is offline.
How did you handel this?

James,

I will take a look at the TDatabase class.

Regards,
Marc

[James Bott]

Marc,

If you are using pessimistic locking this makes the problem worse. By "pessimistic" locking I mean that the record is locked whenever a user is editing a record. When doing this the record can be locked for a long time and there is more chance that a crash could happen.

If you use "optimistic" locking then you only lock the record when the user saves the changes. The record is only locked for a split second and thus there is less chance of a problem.

James

[Marc Vanzegbroeck]

James,

I agree with you in normal case, but in this program I must use that kind of locking.
The program I'm writing is a truck-planning-program for a transport-company. If one user is modifying a route of a driver, other planners are not allowed to change this. The user is also not allowed to drag the route of one driver to another driver if someone else is changing the route...

Regards,
Marc