Version Control

Diomidis Spinellis
Department of Management Science and Technology
Athens University of Economics and Business
Athens, Greece
dds@aueb.gr

Version Control

Tracks project across time
Collaboration, documentation, undo
Open source systems in order of increasing capabilities
- RCS
- CVS
- Subversion, Git, Mercurial, Bazaar

The Great Debate

Centralized (CVS, Subversion)
- Single source of truth
- Pre-commit checks
Distributed (Bazaar, Git, Mercurial, darcs)
- Can work off line
- Easier participation (no committer bit)
- Cheap local commits

Version Control Operations

Central repository keeps historical data
A commit or check-in adds a change into the repository
An update or check-out retrieves a version from the repository
Versions are tracked with version numbers
- Numeric: automatically assigned
- Symbolic: assigned by humans to track milestones
Keywords in the source files are automatically expanded, identifying version, status, author, etc.

Branching

Development can split into different branches e.g.
- Trunk or head
- Stable or release
- Feature
- Vendor
Branches can join again

Revision Tree Example

cat.c revision tree

Life Under a VCS

Import
Update or synchronize
Commit
Label or tag

The Goodies

Identify conflicting changes
Versioning:
- Annotated listings
- Version history
- File differences
Branching
Source of truth
Metrics

Example of a Change Log

RCS file: /cvsroot/basesrc/bin/cat/cat.c,v
Working file: cat.c
head: 1.28
branch:
locks: strict
access list:
symbolic names:
    netbsd-1-5-PATCH002: 1.23
    [...]
    netbsd-1-5: 1.23.0.4
    [...]
    netbsd-1-2-BETA: 1.11
    netbsd-1-2-base: 1.11
    netbsd-1-2: 1.11.0.6
    [...]
keyword substitution: kv
total revisions: 33;    selected revisions: 33
description:
----------------------------
revision 1.28
date: 2001/09/16 12:12:13;  author: wiz;  state: Exp;  lines: +6 -4
Some KNF, via patch by Petri Koistinen in private mail.
----------------------------
revision 1.27
date: 2001/07/29 22:40:57;  author: wiz;  state: Exp;  lines: +6 -6
Some style improvements. [Nearly] #13592 by Petri Koistinen.
[...]
----------------------------
revision 1.15.2.1
date: 1998/02/08 21:45:36;  author: mellon;  state: Exp;  lines: +18 -9
Pull up 1.16 and 1.17 (kleink)

Example of a File Difference List

$ cvs diff -c -r1.12 -r1.13 basesrc/bin/cat/cat.c
Index: basesrc/bin/cat/cat.c
===================================================================
RCS file: /cvsroot/basesrc/bin/cat/cat.c,v
retrieving revision 1.12
retrieving revision 1.13
diff -c -r1.12 -r1.13
[...]
***************
*** 136,141 ****
--- 136,142 ----
                                fp = stdin;
                        else if ((fp = fopen(*argv, "r")) == NULL) {
                                warn("%s", *argv);
+                               rval = 1;
                                ++argv;
                                continue;
                        }

Example of an Annotated Listing

1.166        (jhb      16-Oct-02):      fdp = p->p_fd;
1.114        (alfred   13-Jan-02):      FILEDESC_LOCK(fdp);
1.157        (iedowse  02-Sep-02):      if ((unsigned)fd >= fdp->fd_nfiles ||
1.157        (iedowse  02-Sep-02):          (fp = fdp->fd_ofiles[fd]) == NULL) {
1.114        (alfred   13-Jan-02):              FILEDESC_UNLOCK(fdp);
1.106        (dillon   01-Sep-01):              error = EBADF;
1.106        (dillon   01-Sep-01):              goto done2;
1.106        (dillon   01-Sep-01):      }
1.157        (iedowse  02-Sep-02):      pop = &fdp->fd_ofileflags[fd];
1.94         (dillon   18-Nov-00):
1.157        (iedowse  02-Sep-02):      switch (cmd) {
1.1          (rgrimes  24-May-94):      case F_DUPFD:
1.241        (rwatson  07-Aug-04):              /* mtx_assert(&Giant, MA_NOTOWNED); */
1.158        (jhb      03-Sep-02):              FILEDESC_UNLOCK(fdp);

Extracting Metrics

Changes per source file
Changes per author
Authors per source file
Lines per day
Changes corresponding to bug categories

Tracking Example

Maintainability index over time in the FreeBSD kernel.

Best Practices

Put everything under version control
Use VCS on your personal projects
Think carefully about file name and organization
Perform one separate commit for every change
Label all releases
Establish and follow policies and procedures

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