1. Jump to first page (C) 1998, Arun Lakhotia 1 Software Configuration Management: Version Control Arun Lakhotia University of Southwestern Louisiana Po Box 44330 Lafayette, LA 70504, USA arun@cacs.usl.edu

2. Jump to first page (C) 1998, Arun Lakhotia 2 Software Configuration Management n Practice of handling changes systematically n Three components u Build control u Version control u Change control

3. Jump to first page (C) 1998, Arun Lakhotia 3 Traditional Version Control n Common methods of maintaining versons u Copy versions into separate directories F backup F old F old/old F backup.Feb.7.1988 u Copy versions onto separate disks/diskettes and label the disk

4. Jump to first page (C) 1998, Arun Lakhotia 4 Problems with traditional approach n Inefficient use of storage n Inefficient for storage and retrieval n Inefficient for comparing changes across versions

5. Jump to first page (C) 1998, Arun Lakhotia 5 Common approaches for working in teams n Each person maintains a copy of the system n Every one works on the same copy of the system n A combination of the two

6. Jump to first page (C) 1998, Arun Lakhotia 6 Conflicts when working in teams n Multiple programmers may simultaneously modify u different copies of the same files u same file u inconsistent versions of the files

7. Jump to first page (C) 1998, Arun Lakhotia 7 Version Control Requirements n Provide methods to save the state of a “configuration” at various snapshots in time n Provide methods to revert configuration to an earlier state

8. Jump to first page (C) 1998, Arun Lakhotia 8 Version Control Capabilities n Version control procedure or tool should provide capabilities to: u identify (name) u time/date stamp u store and retrieve u compare multiple versions of u individual components, or u complete configuration, or u some combination thereof

9. Jump to first page (C) 1998, Arun Lakhotia 9 Version control tools n Individual file level control u SCCS u RCS n Directory level control u CVS u Razor

10. Jump to first page (C) 1998, Arun Lakhotia 10 Configuration Repository n A version control tool is essentially a database manager n The database of versions of one or more programs is called a Repository n Process of depositing an item in the repository is called checkin n Process of retrieving an item from the repository is called checkout

11. Jump to first page (C) 1998, Arun Lakhotia 11 Configuration identification n Configuration item u Primitive components whose versions need be controlled n Baseline u State of all configuration items at some particular time u Baselines are typically defined at completion of certain phases F Functional baseline F Design baseline F Product baseline n All changes made after a baseline has been defined must be controlled (I.e., approved, recorded, etc.)

12. Jump to first page (C) 1998, Arun Lakhotia 12 Identifying versions: Numbering n Convention for naming versions. n Numbering convention: u Associate two numbers RR.VV F RR is major release F VV is version F Such as 1.0, 1.1, 1.2, 2.0, 2.1.. n Each configuration item has its own version number n Different configuration item within a configuration may have different version number

13. Jump to first page (C) 1998, Arun Lakhotia 13 Identifying versions: Symbolic n A symbolic name may be assigned to a version number u 2.2 = design-baseline u 3.0 = fully-tested n The “current state” of all configuration items may be given the same symbolic name n Symbolic names may be used to identify the state of the whole system at a given time

14. Jump to first page (C) 1998, Arun Lakhotia 14 Access control n VC tools control the access of configuration items to prevent conflicts when working in team n Common Access Control mechanisms u Lock at check-out u Complain at check-in

15. Jump to first page (C) 1998, Arun Lakhotia 15 Lock at checkout n At any time there can be only one checked out copy of an item n Arbitrary number of copies may be taken to peek n A copy may be checked in only if it has been checked out earlier n When an item is added to a repository it is unlocked

16. Jump to first page (C) 1998, Arun Lakhotia 16 Lock at checkout: State diagram Not in repository lockedunlocked Add to repository Checkout Checkin Peek

17. Jump to first page (C) 1998, Arun Lakhotia 17 Lock at checkout: Example F1.c 1.1 1.2 1.3 F1.h 1.1 1.2 F2.c 1.1 1.2 1.3 1.4 Baseline: Rel-1 Programmer A Programmer B Checkout: F1.c, F1.h Checkout: F2.c Peek: F2.cPeek: F1.c, F1.h Time: T0 Time: T1 Checkin: F1.c Checkin: F2.c Time: T2 Checkout: F2.c Sorry! Not allowed Time: T3 Time: T4 System inconsistent

18. Jump to first page (C) 1998, Arun Lakhotia 18 Complain at checkin n There are NO locks n Anyone may retrieve and modify an item n The first one to checkin a modification is allowed n Subsequent checkins are disallowed. To do so the modifications must be merged with the most recent checkout version

19. Jump to first page (C) 1998, Arun Lakhotia 19 Lock at checkout: Example F1.c 1.1 1.2 1.3 F1.h 1.1 1.2 F2.c 1.1 1.2 1.3 1.4 Baseline: Rel-1 Programmer A Programmer B Checkout ALL Time: T0 Time: T1 Modify: F1.cModify: F2.c Time: T2 Update F1.c Time: T3 Time: T4 Complain! F1.c changed Checkin ALL

20. Jump to first page (C) 1998, Arun Lakhotia 20 Lock at checkout: Analysis n Benefits u Ensures that there are no simultaneous modifications to the same item. n Drawback u Hampers parallel development u Potential for deadlock: two people waiting on each other to release a locked item

21. Jump to first page (C) 1998, Arun Lakhotia 21 Complain at checkin: Analysis n Benefits u Supports parallel development u Enables directory level operations n Drawbacks u Requires sophisticated tools for merging changes u Prolonged delays in checkin may make people out of sync

22. Jump to first page (C) 1998, Arun Lakhotia 22 Summary: Version Control n VC encompasses the tasks involved in managing multiple versions of a (multi- component) system being developed by multiple programmers n There are several tools available that can automate various VC tasks n The VC tools place the source code in a “repository” and provide mechanisms to add, checkin, and checkout items from the repository