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From: COSCB0G@uhvax1.uh.edu (InSik Kim)
Newsgroups: comp.databases,comp.sys.ibm.pc,comp.dcom.lans
Subject: Re: Concurrency Control + Question
Message-ID: <775@uhvax1.uh.edu>
Date: 3 Jul 89 18:15:56 GMT
References: <25232@shemp.CS.UCLA.EDU> <221@ic2020.UUCP> <96@mdi386.UUCP>
Organization: University of Houston
Lines: 51

In article <96@mdi386.UUCP>, bruce@mdi386.UUCP (Bruce A. McIntyre) writes:
> in article <25232@shemp.CS.UCLA.EDU>, gblee@maui.cs.ucla.edu says:
> > Please consider the following problems: ...
> The simple foxbase+ code to lock and edit a record is 
> 	find name       && lookup the correct record.
> 	if rlock()      && returns true if record lock successfull.
> 		edit          && edit this record. ( or modify somehow )
> 		unlock()      && unlock all locks you have set
> 	else
> 		... display message, that you can not lock this record.
> 	endif
> MY QUESTION: 
> The only problem I have had is on some operations that could effect ALL 
> records, Exclusive access is required.  I have not found a simple way
> to gain exclusive access.  Anyone have a simple solution ?
> > --Geunbae Lee,m UCLA-CS-AI.
 
That can be done same way as record locking, i.e.

	USE filename .....	&& use database file
	if FLOCK() 		&& returns true if flie lock successful
		...
		...		&& do the operation
		...
		UNLOCK()        && unlock the file
	else
		... display message
	endif

or, if you want to lock it in loop with time out,

        STORE nnn TO time_out			&& nnn is time_out period
	USE filename				&& use database file
	STORE 0 TO time				&& initialize time
	DO WHILE time <= time_out .OR. FLOCK()
		STORE time+d_time TO time	&& d_time is time interval
	ENDDO
	IF time > time_out			&& file locking failed
		... display message for failure and prepare exit
	ENDIF
	...	&& do the necessary operation
	...
	UNLOCK()

=========================================================================
	InSik Kim  
	University of Houston, University Park           
 	4700 Calhoun, Houston, TX 77004                             
 	InterNet Address                         iskim@crcc.uh.edu
				 		 iskim@cs.uh.edu
=========================================================================