Path: utzoo!attcan!uunet!wuarchive!zaphod.mps.ohio-state.edu!usc!hacgate!ashtate!joeb
From: joeb@ashtate (Joe Budge)
Newsgroups: comp.databases
Subject: Re: rlock() in SCO foxbase+.
Message-ID: <1266@ashton.UUCP>
Date: 24 Sep 90 18:31:23 GMT
References: <553@safn2.UUCP>
Organization: Ashton-Tate, Torrance, CA
Lines: 37

From article <553@safn2.UUCP>, by rey@safn2.UUCP (rey):
> 
> My Dbase IV guide talks about rlock() being cumlative up to 50 locks.
> 	On the same record? Can only 50 different records be locked?

----> A networked PC running dBASE IV under DOS can lock up to 50
      different records at once on a shared file server.  This is per
      PC, so if you had 10 PC's on the net they could lock 500
      different records - though I pity the guy who then comes along
      to try to find an unlocked record <g>.

      If a networked PC needs to lock more records than that, it should
      try for an flock() on the files in question.  A PC can get up
      to 10 flock()'s, since that's how many work areas you have.

      The automatic locking mechanism within dBASE IV looks at the scope
      of the command and determines if it should go for a record lock or
      a file lock.  If you're doing it manually instead (with the rlock()
      and flock() functions) you have to be judicious in selecting the
      appropriate one.
> 
> How are the locks implemented? Are they in the .dbf file header or
> 	in the record being locked or in shared memory (Which I
> 	don't think I am using).

---->  You are using shared memory, you just don't know it.  Networks
       which support the DOS file locking protocols keep a table of
       locks on the server itself.  The table includes filenames,
       owner of the lock, and the range of bytes within the file which
       are locked.  All the products I've ever seen which support locking
       on a DOS network use this protocol.

       When these products are moved to other operating systems, the
       vendors still rely on the operating system itself to maintain the
       locks.

       Joe Budge