Very Computer

I have an ndbm database which could be accessed by more than one
process at a time.  So, of course I want to do file locking.

So I have a few questions which should be vendor independent (I hope).

lockf wants a file descriptor for the first argument, not a pointer to
DBM.

So,

1) Should I open the .pag file RDWR, do a lock on it, and then in
   the same process, do the dbm_open, dbm_store, dbm_close?

2) I would think I'll have to lock the entire file, as that fd isn't
   going to know what offset in the file will point to where
   I am about to write in the .pag file.  Must I lock the entire
   file?

As I said, this would seem to be vendor independent, but I'll mention
that I am running Solaris 2.3+patches on a Sparc 20.

Thanks in advance for any ideas/suggestions/comments.

-rob
---
Rob Francis
Paradigm Systems   <URL:http://www.sf.psca.com/Hyplans/rfrancis/>

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Quote:>So,

>1) Should I open the .pag file RDWR, do a lock on it, and then in
>   the same process, do the dbm_open, dbm_store, dbm_close?

Be aware, though, that none of this should be done on NFS mounted files.
File-locking across machines is still buggy on most Un*xes.

For a discussion of the issues and some useful source code:

Rich Stevens, "Advanced Programming in the UNIX Environment"
[Addison Wesley 1992, ISBN 0-201-56317-7]

Especially Chapter 12, Section 3.

Hope this helps.

Cheers,
ar

Quote:

>>I have an ndbm database which could be accessed by more than one
>>process at a time.  So, of course I want to do file locking.

>No chance.  I have tried this stunt and failed.  You would have a better
>chance using the new Berkeley DB (ftp.cs.berkeley.edu:.../ucb/4bsd/db.tar.Z)
>or GNU's DB.  ndbm doesn't have built-in locking mechanism but the above two
>dbs do.

-rob
---
Rob Francis
Paradigm Systems   <URL:http://www.sf.psca.com/Hyplans/rfrancis/>

Quote:>I have an ndbm database which could be accessed by more than one
>process at a time.  So, of course I want to do file locking.

        My_Program (client - multiple instances)
                        |
                        |       <--- RPC interface - function calls
                        |            like dbm_put, dbm_get, etc.
                        |
                ndbm daemon process (ONE instance)
                        |
                        |
                ndbm database

Effortlessly wipes out your integrity hassles.   No need for locking,
and if you DO want to lock (eg during a "list all"), just add it
internally to the dbm server (remember to put in a timeout - in case
user hits ctrl-C or something).

It works better than ANY application I've seen that uses .lock files
or similar - and some of these fetch mega-$.