Re: File Locking Problems?

Locking occurs on several different levels.  
  -- Object (File) Level
  -- Member Level
  -- Record Level

Whenever a program opens a file, it issues both an object lock and a
member lock to prevent someone from deleting the file, or removing the
member while your program is running.  (This also protects against many
other things, but you get the idea...)

The CHAIN(N) refers to a "record lock".  When you lock a record, it 
prevents other programs from locking that same record.  Since you must
lock it to update it, the record lock protects you against other
programs updating the record while your program is trying to change it.

Its important to make the distiction between a "record lock" and a "file
lock".   The fact that you're using CHAIN(N) and therefore not locking the
record has nothing whatsoever to do with whether another program is able
to "open" the file.   It would only prevent another program from reading
the record that you've locked.

An "Open" problem would be a file or member level lock.  Perhaps you're 
using the CL command "ALCOBJ" to get exclusive use of the file?  Or doing
something else that prevents other programs from opening the file?  

In any case, a trigger program should "never" need to open the file that
its being triggered on!  Never!  The buffer containing the before and
after record images are passed as parameters, and your trigger can read &
write data directly to those images!  Assuming that the trigger is a 
*BEFORE trigger, and that you used ALWREPCHG(*YES) on the ADDPFTRG
command, the changes you make to the "after" buffer will be placed into
the file without you needing to issue an UPDATE or WRITE.

(This seems to be a very popular topic on this list this week!)

Hope that helps...  (and hope I made sense...)



On Tue, 21 Mar 2000, a b wrote:

> I'm attempting to call a program from a trigger, but
> I'm getting an error indicating that the application
> is unable to open the file.  I've notice that it locks
> the files eventhough I' added the CHAIN(N).  I don't
> quite understand why it would lock all of the files. 
> Is there a way to avoid this?  Is there a CL command
> that "UNLOCKS" all of the file that are being used. 
> For example, I call a CL that calls the RPG, then
> returns to the CL who in turn "UNLOCKS" all of the
> files used...  or is there a better way?  Any help
> would greatly be appreciated.
> 

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