Held: Monday, 20 September 2004
Summary:
Today we consider issues in sharing and versioning files. We also consider
CVS, a particular tool to support such tasks.
Related Pages:
Overview:
- Background: Controlling Source Code
- Background: Unix tool design
- CVS: Design Issues
- Using CVS
- By this point in your careers, most of you have worked primarily on small projects, both by yourself and with others.
- Working with groups creates a few basic problems. They include:
- How do you handle the problem that different people may be working different files?
- How do you keep track of old versions of files?
- What happens when two people decide to work on the same file?
- How do you distinguish between the working and the
last usable
version of a file.
- These problems get even worse when you work with larger teams and larger projects.
- It becomes particularly important to keep old versions of code around in case you introduce subtle (or not so subtle) bugs and want to "roll back" your code.
- Most project management systems provide some solution to these problems.
- In the world of Unix, the original "primary players" were SCCS, the source code control system, and RCS, the revision control system.
- Both fell within the Unix model of tool design: Instead of building one, huge, tool, you build lots of small tools that interact well together.
- Hence, SCCS and RCS only do revision and access control. They don't worry about other issues in project management.
- What other issues are there? Loads. Deciding on the appropriate way to group files. Recompilation of selected files. Keeping track of time spent on the project.
- Both use a
library
model for file sharing: Only one person can have a file checked out
for modification at a time. (However, more than one person can read the file.)
- SCCS and RCS served as the primary Unix revision and access control tools for many years.
- As the Internet grew, programmers found more and more problems.
- Both are designed for programmers working on a single system. The growth of the Internet led to a world in which people worked collaboratively on multiple systems.
- Both assume that only one person should modify a file at a time.
- Experience showed that some folks
checked out
files and forgot to check them back in.
- Experience suggested that in many cases, when two people want to modify the same file, they modify different parts. (RCS folks would suggest that you didn't segment your project appropriately.)
- At the same time, the Internet needed better ways to distribute software in source form.
- CVS grew out of these, and related, problems.
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Check with Bobby