Foxpro for DOS 2.6 record locking

Posted on 2013-11-10
Medium Priority
Last Modified: 2013-11-12
I have been asked about record and file locking in Foxpro for DOS 2.6. What would be the best way to approach record locking for record writes/updates? What about file locking?
Question by:Idarac
LVL 30

Expert Comment

by:Olaf Doschke
ID: 39637276
It's like asking what is the best way to use a kitchen.

The topic locking is a bit narrower, still if you ask this question without telling what you expect of locking and how your application should work, you better first read about what locking can do for.

First of all locks are only needed for multi user environments. Is your dos app multi user at all?

Bye, Olaf.
LVL 43

Accepted Solution

pcelba earned 2000 total points
ID: 39637284
Several concepts exist:

1) Do nothing and FoxPro will lock records/files automatically. You just need to process possible error messages when the lock fails.

2) Explicit file/record locking by FLOCK()  or  RLOCK() - lock the record if you are updating it, lock the file if you are updating more records. You may split this approach into two parts:

a) pessimistic locking - lock the record/file before you start editing it
b) optimistic locking -  lock the record/file just before you save your changes to it

Pessimistic locking can block your application if several users are updating same record/file. Optimistic locking is also called "The last is the winner" - changes made by the last user saving data into a file/record represent the final record/file contents.

I am using record locking for header table and automatic locking for line tables obviously. (I suppose if the Order/Invoice header is locked by me then nobody else will write to appropriate order/invoice lines.)

To have your application running smoothly the record and namely the file should remain locked as short time as possible. Never leave the record/file locked when you are waiting for user response. If this is necessary then all READ commands should have timeout activated to avoid application blocking.

You should study following commands/functions in the FoxPro help:
LVL 27

Expert Comment

ID: 39637830
The usual approach to locking a single record:

IF RLOCK('table')
    DO stuff
    UNLOCK IN table
    WAIT WINDOW "Record is locked by another user".

Open in new window


Author Closing Comment

ID: 39641764
Great answer

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Microsoft Visual FoxPro (short VFP) is a programming language with it’s own IDE and database, ranking somewhat between Access and VB.NET + SQL Server (Express). Product Description: http://msdn.microsoft.com/en-us/vfoxpro/default.aspx (http://msd…
Configure external lookups on for external mail flow on Exchange 2013 and Exchange 2016.
The video provides a quick and easy steps to migrate MBOX file to well known Outlook PST and Office 365. Besides this, it also supports and migrates more than 20 email clients of MBOX which include AppleMail, Opera, Thunderbird and SeaMonkey effortl…
Through the video, you can check the migration process of Outlook PST file to PDF. Kernel for Outlook to PDF tool can convert Outlook emails with all attributes like Subject, To, From, Cc, Bcc and other folders such as Inbox, Outbox, Sent Items, Jun…

627 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question