Choosing CVS with Reserved or Unreserved checkouts.

What is CVS?

CVS is the Concurrent Version System from the Free Software Foundation (GNU). It is re-distributed by several other vendors.

The Concurrent Versions System is a front end to the RCS revision control system which is similar to but is often considered to be better than, SCCS (e.g.: RCS baselines the most recent version and keeps deltas for earlier ones).

CVS can be used with a shared or non-shared central repository (single user mode is also known as :local: mode).

If you have not already done so, please read A methodology to Uniface source code control before you continue with these topics and examples.

Reserved versus Unreserved checkouts

The software development methodology which CVS is designed for is unusual to most configuration managers and software developers who have used other version control tools. This methodology is known as Unreserved Checkouts.

For this reason it may not be the ideal choice of version control. Naturally UD6 works equally well with all other commercial source code managers including PVCS Dimensions, ClearCase, Visual SourceSafe and many others.

Reserved checkouts

This is the most common form of source code management. A central "checked out" copy of the source code is maintained, and developers check out the piece(s) of code they are working on. These are copied to an area where the developer can update the file.

When the developer is finished, the file can be checked back in, and the "Reference area" updated. Multiple developers cannot usually work on the same file at the same time using this technique.

We have provided a guide for how UD6 and Uniface can be used with CVS in this manner, however since CVS is not designed to work this way most manuals or 3rd party software (such as WinCVS) will not work well with CVS when used this way.

Unreserved checkouts

Most CVS users use this technique.

A central repository of all versions of the software exists in a central location (usually a server), and each developer has their own complete copy of the source code tree (usually on a local disk).

Developers can be automatically informed when a file they are using is modified by someone else (known as a watch).

Changes performed by 2 developers at the same time are merged when the code is checked in.

Many 3rd party tools exist to simplify using CVS in this mode including several tools for Windows: WinCVS and Tortoise.

March hare have also provided a guide for Uniface users who want to use UD6 with CVS in this configuration.