Version Control Systems. Copyright 2017 by Robert M. Dondero, Ph.D. Princeton University

Size: px

Start display at page:

Felicia Craig
5 years ago
Views:

2 Objectives You will learn/review: Version control systems (VCSs), as mechanisms for Maintaining file versions Safely sharing files with teammates 2

3 Toward Generation 1 Problem Programming involves discovery Discovery involves making mistakes Programmers sometimes must revert to a previous version Programmers require versioning Programmers require a version control system (VCS) 3

4 Toward Generation 1 Solution: VCS generation 1 Provides versioning Popular system: RCS Still bundled with Linux Readily available for Mac and MS Windows Example: 4

5 Generation 1 Local repo boldface => file is read-only Working 5

6 Generation 1 Local repo (1) checkout A Working 6

7 Generation 1 Local repo (2) edit A A B C Working 7

8 Generation 1 A A B C Local repo (3) checkin A A B C Working Old version of file A is retained in local repository Old version can be retrieved to if necessary 8

9 Toward Generation 2 Problem: Programmers often must work in teams Programmers need both version control and file sharing 9

10 Toward Generation 2 Solution: VCS generation 2 Version control + central repository 10

11 Generation 2 11

12 Generation 2 (1) pull 12

13 Generation 2 (2) pull 13

14 Generation 2 A B C (3) edit 14

15 Generation 2 A B C A B C (4) edit 15

16 Generation 2 A A B C (5) push A B C A B C 16

17 Generation 2 A A B B C (6) push A B C A B C 17

18 Generation 2 A A B B C (7) pull A B C A B C 18

19 Generation 2 A A B B C (8) pull A B C A B C 19

20 Toward Generation 2a Problem: Conflicts Example: 20

21 Toward Generation 2a 21

22 Toward Generation 2a (1) pull 22

23 Toward Generation 2a (2) pull 23

24 Toward Generation 2a A B C (3) edit 24

25 Toward Generation 2a A B C A B C (4) edit 25

26 Toward Generation 2a A A B C (5) push A B C A B C 26

27 Toward Generation 2a A A A B C (6) push edits are lost in central repo!!! A B C A B C 27

28 Toward Generation 2a A A A B C (7) pull A B C A B C lost her own edits!!! 28

29 Toward Generation 2a A A A B C (8) pull A B C A B C Bob never receives edits!!! 29

30 Generation 2a Solution: VCS generation 2a Version control + central repo + locking Programmer requests lock on file A VCS grants lock iff file A currently is unlocked Popular system: PVCS Example: 30

31 Generation 2a boldface => file is read-only 31

32 Generation 2a (1) lock and pull A box => file is locked 32

33 Generation 2a (2) lock and pull A Denied 33

34 Generation 2a A B C (3) edit 34

35 Generation 2a A A B C (4) push and unlock A A B C 35

36 Generation 2a A A B C (5) lock and pull A Accepted A B C A B C 36

37 Generation 2a A A B C A B C A B C (6) edit 37

38 Generation 2a A A A B C (7) push and unlock A A B C A B C 38

39 Generation 2a A A A B C (8) pull A B C A B C 39

40 Toward Generation 2b Problems: Awkward administration Alice forgets to unlock A (and goes on vaca!) Unnecessary serialization Alice and Bob may be editing different parts of A Potential deadlock Suppose A & B depend upon one another Alice locks A; Bob locks B Alice needs lock on B; Bob needs lock on A 40

41 Generation 2b Solution: VCS generation 2b Version control + central repo + merging Popular systems: Concurrent Versioning System (CVS), Subversion, Perforce Example: 41

42 Generation 2b 42

43 Generation 2b (1) pull 43

44 Generation 2b (2) pull 44

45 Generation 2b A B C (3) edit 45

46 Generation 2b A B C A B C (4) edit 46

47 Generation 2b A A B C (5) push A B C A B C 47

48 Generation 2b A A B C (6) push Conflict! Denied! A B C A B C 48

49 Generation 2b A A B C (7) pull A B C A A B C 49

50 Generation 2b A A B C A B C A B C (8) merge 50

51 Generation 2b A A A B C (9) resolve & push A B C A B C 51

52 Generation 2b A A A B C (10) pull A B C A B C 52

53 Toward Generation 3 Problems: Tough to work offline No versioning Single point of failure Server down => no versioning or sharing corrupted (and no backup) => project history lost Constrained workflow (More soon in this lecture) 53

54 Toward Generation 3 Solution: VCS generation 3 Version control + distributed repos + merging Popular systems: Git, Mercurial Example: 54

55 Generation 3 repo repo 55

56 Generation 3 (1) pull repo repo 56

57 Generation 3 repo A B C repo (2) edit 57

58 Generation 3 repo A A B C A B C repo (3) commit 58

59 Generation 3 A A B C (4) push repo A A B C A B C repo 59

60 Generation 3 A A B C (5) pull repo A A B C A B C A A B C A B C repo 60

61 Generation 3 A A B C repo A A B C A B C A A B C A B C repo (6) edit 61

62 Generation 3 A A B C repo A A B C A B C A A B B C A B C repo (7) commit 62

63 Generation 3 A A B B C (8) push repo A A B C A B C A A B B C A B C repo 63

64 Generation 3 A A B B C (9) pull repo A A B B C A B C A A B B C A B C repo 64

65 Generation 3 Topologies sitory is not special Programmers can pull from any repo Programmers can push to any repo Permits variety of topologies 65

66 Centralized Topology Official repo Pgmmer 1 repo Pgmmer 2 repo Pgmmer 3 repo Each programmer merges into shared repository Probably sufficient for COS 333 project 66

67 Integration Mgr Topology Official repo Pgmmer 1 repo Pgmmer 2 repo Integration mgr repo Integration manager pulls from programmers Integration manager does all inter-programmer merges Integration manager pushes to official repo 67

68 Dictator & Lieutenants Topology Dictator repo Official repo Lieutenant 1 repo Lieutenant 1 repo Pgmmer 1 repo Pgmmer 2 repo Pgmmer 3 repo 68

69 Dictator & Lieutenants Topology Each lieutenant: Manages one subsystem Pulls from programmers on that subsystem Dictator: Manages the project as a whole Pulls from lieutenants 69

70 Generation 3 Workflows Richer topologies allow for richer workflows The primary advantage of Generation 3 systems???

71 Next Steps Learn about Git See Git and GitHub Primer (Dondero) Available via Topics web page See Git tutorial book: See Git reference manual: 71

72 Summary We have covered: Version control systems (VCSs), as mechanisms for Maintaining file versions Safely sharing files with teammates 72

Version Control Systems (Part 1)

Version Control Systems (Part 1) i i Systems and Internet Infrastructure Security Institute for Networking and Security Research Department of Computer Science and Engineering Pennsylvania State University, University Park, PA Version