1. Concurrent Version Control

2. Introduction What is concurrent version control?
A software package for simplifying team development of software
Why use a version/content control system?
Keeps track of changes made to files under its control
Allows multiple team members to work on a set of project files concurrently
Others
Protect yourself from yourself by preserving old version; can undo changes that don’t work out
Recording an audit trail to show progress made

3. Two Major Issues Version Control Content control
Maintain prior and current versions of files
Allow retrieval of prior versions if necessary
Allow auditing of changes made over time
Content control
Manage concurrent access
Support resolution of conflicts (e.g. two developers make changes in one file at the same time)

4. Two Major Models Client-Server Distributed Repository on server
Clients interact with server
Examples: SVN, Team Foundation Server
Distributed
Each working node keeps a local repository
Exchange of changes follows local work
Examples: Git, Mercurial

5. Example Products CVS (Concurrent Versioning System)
Early historical product
Subversion – currently available at UWEC
“A better CVS” – open source, easier to work with
Variants of this
Visual SVN
Other popular products: Git, Mercurial, Team Foundation Server (MS)
Often now combined with hosting: e.g. Bitbucket (for Git and Mercurial)
Many more 3rd Party Commercial and Open Source Products

6. Introduction to Subversion
What does Subversion Do?
Records creation and modification history of files
Efficiently records every version
Helps developers work concurrently by providing “check-in”, “check-out”, and “synchronize”
What can I do with Subversion?
Get existing file
Publish new version for common use
Compare differences between versions
Create, delete, change permissions, etc.

7. SVN Concepts (1) Has two parts (client-server model): Server Clients
Controls access to common repository of resources
Runs on separate server machine
Clients
Use access to server to create local copies for editing
Come in a variety of forms: command line, Windows App, Plug-in
Repository
Developer 1 2 3 4

8. SVN Concepts (2) Terminology: Repository Working Copy or Workspace
Location of common copy of files
Subversion Server controls access to this special file structure
Working Copy or Workspace
Copy of files on your local drive (generally H: or W: drive for us)
Project
A complete development task in a folder/directory
Can include models, packages, source and other sub-folders, code, graphics, config files, …
Check Out
Get working copy from the Repository
Commit / Check In
Process of saving changes to the Repository
Synchronize or Update
Process of updating the local files to correspond with the repository
Conflict
A disagreement between an edited file in the Workspace and the copy in the Repository

9. Control Models Pessimistic Model
Files become locked on check-out
Only that person with check-out copy can make changes
Optimistic Model (CVS, Subversion, others)
Files not locked on check-out
Conflicts are managed at check-in (rare)
On check-in, official repository copy is compared with new copy
Check timestamp
Line-by-line comparison
- Changes to different lines OK
- Changes to same lines rejected/mediated

10. Example Angela and Hassan both have copies of a.java#5
Angela commits her changes
Creates a.java#6
Then Hassan wants to commit his changes
Conflict!

11. Issues
How many versions of a file do you need to keep in the repository?
Just one; you can get at older versions (e.g. your “backup copy”) through Subversion, and the repository is/should be backed up
How are the old versions of files stored?
A baseline version is created at the beginning, and at each revision some sort of record of the changes is stored
Whole copies of new versions are not kept (expensive in terms of storage)

12. Version Control Concepts (6)
What if I have a “risky” development task that I’m not sure I want to integrate into the source?
You can develop a separate branch and merge back into the trunk later (see online documentation)
Overall, Subversion does not have a good reputation for parallel development, as merging takes time and energy

13. Basics of Using Subversion with TortoiseSVN
- TortoiseSVN – windows explorer-based client
- Assume Subversion repository on server
- Getting Set Up
Create directory for work on local system
Create files in directory
At directory level, right click, TortoiseSVN, Import
Specify URL of repository, click OK
Files in directory will be added to repository

14. Basics of Using Subversion with TortoiseSVN (2)
Assume Subversion repository on server
Working with Files
Go to local working directory, clear out contents that may have same names
On that folder, right-click, SVN Checkout
Specify the URL of Repository
Specify the Checkout directory (your local directory above)
If don’t want subfolders, check “Only check out the top folder”; choose revision you want, OK

15. Basics of Using Subversion with TortoiseSVN (3)
Assume Subversion repository on server
Working with Files (2)
Files will be transferred to local directory
On folder, right-click, SVN Update (if time passed) to ensure files are current as to repository
Make changes to local file(s)
On folder, right-click, SVN Commit
Can add message if desired; OK
Changed files committed to repository

16. Basics of Using Subversion Under Eclipse
Assume Subversion repository on server
Change Eclipse perspective to SVN Repository Exploring
Add the project under Subversion control
Checkout working copy of project
Update local copy (if time has passed)
To ensure you are consistent with current version
Modify local files
Only the ones for which you’re responsible
Commit changes to repository
Only after EXTENSIVE TESTING

17. Concurrent Version Control and Security
http uses a very basic level of security (user/pass to base 64 encoding)
Access to repository relatively (but not entirely) secure in switched network
Access to SVN repository insecure if on wireless, hub, etc.
https is better (user/pass is encrypted)

18. References
“Version Control with Subversion” – online book