10. Multiple developers
When more than one person works on a software project
things often get complicated. Often, two people try to
edit the same file simultaneously. One solution, known
as file locking or reserved checkouts, is
to allow only one person to edit each file at a time.
This is the only solution with some version control
systems, including RCS and SCCS. Currently
the usual way to get reserved checkouts with CVS
cvs admin -l command (see section admin options). This is not as nicely integrated into
CVS as the watch features, described below, but it
seems that most people with a need for reserved
checkouts find it adequate.
It also may be possible to use the watches
features described below, together with suitable
procedures (not enforced by software), to avoid having
two people edit at the same time.
The default model with CVS is known as
unreserved checkouts. In this model, developers
can edit their own working copy of a file
simultaneously. The first person that commits his
changes has no automatic way of knowing that another
has started to edit it. Others will get an error
message when they try to commit the file. They must
then use CVS commands to bring their working copy
up to date with the repository revision. This process
is almost automatic.
CVS also supports mechanisms which facilitate
various kinds of communication, without actually
enforcing rules like reserved checkouts do.
The rest of this chapter describes how these various
models work, and some of the issues involved in
choosing between them.