An Introduction to SCM

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An Introduction to SCM GForge

• Lin Guo
• guolin_at_cs.cornell.edu

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Roadmap

• What is SCM
• Why do we need SCM
• Interesting SCM features
• SCM tools
• GForge
• Conclusion

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What is SCM

• Source Control Management
• Maintain a repository of source files
• Track all changes
• Control changes
• Software Configuration Management
• More than source control
• Manage source repositories

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Why we need SCM

• Source Control
• Sharing supports concurrent development
  
• Versioning provide version number and dates
• Change tracking find details of a change
• Archival reproduce any file from any point
• Documentation, drawing, etc.
• Configuration Management
• Branch release version vs. develop version
• Snapshot of the whole system
• Prohibit further check-in before release

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Roadmap

• What is SCM
• Why do we need SCM
• Interesting SCM features
• Source control vocabulary
• Code Sharing
• Branch
• Label
• SCM tools
• GForge
• Conclusion

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Source Control Vocabulary

• Update obtain the latest versions of the code
• Check-out obtain the writable version of files
• Check-in commit the changes to files
• Lock/unlock one only person may modify a file
• Integrate combines the changes with others
• Add/delete add/remove files to repositories
• Top-of-trunk most updated

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Roadmap

• What is SCM
• Why do we need SCM
• Interesting SCM features
• Source control vocabulary
• Code Sharing
• Lock
• Sharing
• SCM tools
• GForge
• Conclusion

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Code Sharing

• Multiple people can work on the same source base
  without colliding ---
• (1) Lock locks individual files so only one
  person at a time can modify it or
• (2) Merge Allows multiple people to modify a
  source file and the system will automatically
  merge the changes (usually)

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Locking

• Only one person can modify certain source files.
• Works fairly well if developers work on different
  areas of the project and dont conflict often
• Problem 1 People forget to unlock files when
  they are done
• Problem 2 People work around locking by editing
  a private copy and checking in when the file is
  finally unlocked - easy to lose changes.

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Merging

• Several people can work on a file at once
• Before committing changes, each user merges their
  copy with the latest copy in the database
• This is normally done automatically by the system
  and usually works, but you should not blindly
  accept the result of the merge

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Roadmap

• What is SCM
• Why do we need SCM
• Interesting SCM features
• Source control vocabulary
• Code Sharing
• Branching
• SCM tools
• GForge
• Conclusion

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Branching

• Brach sources for different purposes
• When a new version ships, typically create a
  branch for maintenance
• Companies ship several products from the same
  source base
• Branching repository fork and branch off the
  base repository.
• Double update (manually) merge back changes in
  the branching repository

1.0
1.0.1
2.0
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Roadmap

• What is SCM
• Why do we need SCM
• Interesting SCM features
• Source control vocabulary
• Code Sharing
• Branching
• Labeling
• SCM tools
• GForge
• Conclusion

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Labeling

• Label all the files in the source base that make
  up a product at each milestone
• Just before and just after a major change (eg.
  changing several interfaces)
• When a new version ships, want to fix fatal bugs
  in the original version.

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Roadmap

• What is SCM
• Why do we need SCM
• Interesting SCM features
• SCM tools
• GForge
• Conclusion

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CSM Tools

• RCS revision control system
• In most Unix system, only source control
• CVS concurrent versions system
• Free in linux, also support configuration
  management
• SourceSafe
• well-integrated into other Microsoft developer
  products, but not on other platforms
• ClearCase
• commercial CSM tool
• SourceGorge (Gforge)
• Projects are available for public discovery and
  development
• http//gforge.cis.cornell.edu/ (http//gforge.org)
  

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Helpful Rules

• Archived Files Should Always Compile
• Update to get your codes top-of-chunk
• Code review
• Compile and run latest archived files as a set
  before Check-in
• No Cheating (even simple bug fixes)
• Release a lock after you are done.
• Dont overwrite someone elses code

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Roadmap

• What is SCM
• Why do we need SCM
• Interesting SCM features
• SCM tools
• GForge
• Conclusion

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GForge
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GForge

• GForge is an online SCM system
• SCM tools create and control access to CVS and
  Subversion
• Collaborating tool forums and mailing lists
• Access control over the automatically created
  repository depending on the role settings of the
  project
• File release, document management, news
  announcements, surveys, task managements, etc.
• Gforge in Cornell CIS
• https//gforge.cis.cornell.edu/

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GForge
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GForge
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GForge
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GForge
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GForge
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GForge
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Conclusion

• SCM tools are Very Helpful
• GForge is a Good Project Tools Available at CIS

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RCS

• File management only
• Transaction model
• check out and lock
• edit
• check in and unlock
• Little support for binaries

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CVS

• Built on top of RCS
• Therefore little support for binaries
• Database can be remote
• No locking merge before commit
• Fast
• Integrates with emacs

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SourceSafe

• Microsofts entry into the field
• Project-based
• Checkout-edit-checkin model
• Built-in web site creation tools
• Integrates with MSDEV

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Clearcase

• Clearcase is configuration management on steroids
• You create a view of the database with a config
  spec, which describes how to select files from
  the database.
• When you set a view, Clearcase creates a virtual
  filesystem containing only those versions of the
  files selected by the config spec

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SourceForge

• On-line Version Control System
• Projects are available for public discovery and
  development
• A very good environment for open source projects