version control with subversion speaker: chen-nien tsai adviser: kai-wei ke date: 2006.01.17
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Version Control with Subversion
Speaker: Chen-Nien TsaiAdviser: Kai-Wei KeDate: 2006.01.17
2006/1/3 2
Outline• Introduction• Basic Concepts
– Repository– Versioning Models
• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion
2006/1/3 3
Introduction• The Concurrent Versions System
(CVS) has long been the tool of choice for version control.
• Subversion is a relatively new version control system designed to be the successor to CVS.– an open-source system with a design
(and “look and feel”) similar to CVS.– attempting to fix most of CVS's
noticeable flaws.
2006/1/3 4
What is Subversion?• Subversion is a free/open-source
version control system. – Subversion manages files and directories
over time.– Files are placed into a central
repository.– It allows you to recover older versions of
your data, or examine the history of how your data changed (a time machine).
– Subversion can access its repository across networks.
2006/1/3 5
Outline• Introduction• Basic Concepts
– Repository– Versioning Models
• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion
2006/1/3 6
Repository (1/2)• Subversion is a centralized system
for sharing information.• A repository is a central store of
data.
2006/1/3 7
Repository (2/2)• The repository is a kind of file server.• The Subversion repository remembers
every change ever written to it.– every change to every file.– even changes to the directory tree.
• The clients can– see only the latest version of the
repository.– view previous states of the repository.
2006/1/3 8
Repository Layout (a common way)• Ex. SVN repository
– http://svn.collab.net/viewcvs/svn/
• trunk– Main line of development.
• tags– Contain tag copies.– Some projects name it release.
• branches– Contain branch copies.
2006/1/3 9
Repository URLs • Subversion repositories can be
accessed through many different methods.
WebDAV stands for "Web-based Distributed Authoring and Versioning". It is a set of extensions to the HTTP protocol which allows users to collaboratively edit and manage files on remote web servers.
2006/1/3 10
Versioning Models• The core mission of a version control
system is to enable collaborative editing and sharing of data.
• Different systems use different strategies to achieve this. – File-sharing Model– Lock-Modify-Unlock Model– Copy-Modify-Merge Model
2006/1/3 11
The Problem of File-Sharing• Suppose we have two co-workers,
Harry and Sally. (When Harry Met Sally)
• Two users read the same file.• They both begin to edit their copies.• Harry publishes his version first.• Sally accidentally overwrites Harry’s
version.
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Two users read the same file
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They both begin to edit their copies
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Harry publishes his version first
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Sally accidentally overwrites Harry’s version
Harry's work is effectively lost
2006/1/3 16
The Lock-Modify-Unlock Solution• Harry locks file A, then copies it for
editing.• While Harry edits, Sally’s lock
attempt fails.• Harry writes his version, then
releases his lock.• Now Sally can lock, read, and edit
the latest version.
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Harry locks file A, then copies it for editing
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While Harry edits, Sally’s lock attempt fails
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Harry writes his version, then releases his lock
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Now Sally can lock, read, and edit the latest version
2006/1/3 21
The Problem with the Lock-Modify-Unlock Model• Locking may cause administrative problems.
– Sometimes Harry will lock a file and then forget about it.
• Locking may cause unnecessary serialization. – What if they want to edit the different parts of
the same file?
• Locking may create a false sense of security.– Two files edited by different workers may
incompatible.
2006/1/3 22
The Copy-Modify-Merge Solution• Subversion, CVS, and other version
control systems use a copy-modify-merge model.
• Each user's client creates a personal working copy.
• Users then work in parallel, modifying their private copies.
• The private copies are merged together into a new, final version.
2006/1/3 23
An Example
• Two users copy the same file.• They both begin to edit their copies.• Sally publishes her version first.• Harry gets an out-of-date error.• Harry compares the latest version to
his own.• A new merged version is created.• The merged version is published.• Now both users have each other’s
changes.
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Two users copy the same file
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They both begin to edit their copies
2006/1/3 26
Sally publishes her version first
2006/1/3 27
Harry gets an out-of-date error
Out-of-date
2006/1/3 28
Harry compares the latest version to his own
Merging
2006/1/3 29
A new merged version is created
A miracle?
Even a conflict occur?
2006/1/3 30
The merged version is published
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Now both users have each other’s changes
2006/1/3 32
Conflicts• What if Sally's changes do overlap
with Harry's changes?• This situation is called a conflict.
– The system will notify the user if it happened.
– The system can’t automatically resolve conflicts.
– The user has to manually resolve it.
• In practice, conflicts are infrequent.
2006/1/3 33
Outline• Introduction• Basic Concepts
– Repository– Versioning Models
• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion
2006/1/3 34
Basic Work Cycle• Initial checkout
– svn checkout
• Update your working copy– svn update
• Commit your changes– svn commit
• Make changes– svn add, svn delete, svn copy, svn move
• Examine your changes– svn diff, svn status, svn revert
2006/1/3 35
Initial Checkout• Checking out a repository creates a
copy of it on your local machine. • This copy contains the HEAD (latest
revision) of the Subversion repository.
• Example– svn checkout
http://140.124.181.245/repos/Test[chennien@netlab2 tmp]$ svn checkout http://...A Test/trunkA Test/trunk/WSS.hA Test/trunk/WSS.cppA Test/branchesA Test/tagsChecked out revision 1.
2006/1/3 36
Update Your Working Copy• Update your working copy to receive
any changes made by other developers.
• Example– svn update[chennien@netlab2 trunk]$ svn update
U WSS.cppUpdated to revision 2.
2006/1/3 37
Commit Your Changes• Commit your changes to the repository. • Example
– svn commit --message “log message.”
• Each time the repository accepts a commit, this creates a new state of the repository, called a revision.
[chennien@netlab2 trunk]$ svn commit -m “log message"Sending trunk/WSS.cppTransmitting file data .Committed revision 4.
2006/1/3 38
Resolve Conflicts• If you get a conflict, you need to do
one of three things: – Merge the conflicted text “by hand.”– Copy one of the temporary files on top of
your working file. – Run svn revert <filename> to throw
away all of your local changes.
• Once you've resolved the conflict, you need to let Subversion know by running svn resolved <filename>.
2006/1/3 39
Outline• Introduction• Basic Concepts
– Repository– Versioning Models
• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion
2006/1/3 40
Branch, tag, and Merging• Branch, tag, and merging are
concepts common to almost all version control systems.
• Branch: a line of development that exists independently of another line.
• Tag: just a snapshot of a project in time.
• Merging: merge two revisions.
2006/1/3 41
Why Branch?• Suppose you’ve been given the task of
performing a reorganization of the project.
• It will take a long time to write, and will affect all the files in the project.
• If you start committing your changes bit-by-bit, you'll surely break things for other developers.
• Solution: create your own branch, or line of development, in the repository.
2006/1/3 42
Branches
2006/1/3 43
Branches• Creating Branches
– A common policy is to place branches in the /project_name/branches directory.
– Using svn copy command.
• Example– svn copy trunk branches/my-branch
svn commit –m “message”[chennien@netlab2 Test]$ svn copy trunk branches/my-branchA branches/my-branch[chennien@netlab2 Test]$ svn commit -m "message"Adding branches/my-branchAdding branches/my-branch/WSS.cppCommitted revision 5.
2006/1/3 44
Tags (1/2)• A tag is just a “snapshot” of a project
in time. • Creating tags
– the same procedure to create a branch– A common policy is to place tags in
the /project_name/tags directory.
• Example– svn copy trunk tags/release-1.0
svn commit –m “message”
2006/1/3 45
Tags (2/2)
[[chennien@netlab2 Test]$ svn copy trunk tags/release-1.0A tags/release-1.0[chennien@netlab2 Test]$ svn commit -m "tag"Adding tags/release-1.0Adding tags/release-1.0/WSS.cpp
Committed revision 6.
2006/1/3 46
Merging• To merge all of your branch changes
back into the trunk.• Example
– svn merge -r 5:8 http://140.124.181.245/repos/Test/branches/my-branch
[chennien@netlab2 trunk]$ svn merge -r 5:8 …U WSS.cpp[chennien@netlab2 trunk]$ svn commit -m "after merge"Sending trunk/WSS.cppTransmitting file data .Committed revision 9.
2006/1/3 47
Resources
• Version Control with Subversion (books)– http://svnbook.red-bean.com/
• Subversion (the project home)– http://subversion.tigris.org/
• TortoiseSVN (a subversion client for windows 2k or higher)– http://tortoisesvn.tigris.org/
• ViewCV (a browser interface)– http://viewvc.red-bean.com/
2006/1/3 48
ViewVC• It is a browser interface for CVS and
Subversion version control repositories. • It provides the report-like functionality,
but much more prettily than the textual command-line program output.
• http://dev.eclipse.org/viewcvs/index.cgi/• http://svn.collab.net/viewcvs/svn/• http://140.124.181.245/~netlab/cgi-bin/
viewcvs.cgi
2006/1/3 49
Conclusions• The heart of any version control
system– they are designed to record and track
changes to data over time.– to enable collaborative editing and
sharing of data.
• Subversion can manage any sort of file collection—it's not limited to helping computer programmers.
2006/1/3 50
There are more• Repository Administration
– How to create a repository?
• Server Configuration– svnserve server and SSH tunnel.
• Software Development Policy– Any guideline for committing changes?– When should the trunk become a release
(tag)?
Backup Materials
2006/1/3 52
2006/1/3 53
Resources• Other Browser interfaces
– Easy SVN Browser– WebSVN– SVN::Web
2006/1/3 54
We all have our time machines. Some take us back, they're called memories.
Some carry us forward, they're called dreams.
2006/1/3 55
What is the trunk? • The trunk is the central source code
that is used for continuous and ongoing development. Trunk builds contain the very latest bleeding-edge changes and updates. However, the trunk can also be very unstable at times, so it's good to ask around before using trunk builds.
• MozillaZine– http://forums.mozillazine.org/viewtopic.php?t
=305281
2006/1/3 56
What is a branch? • Branches are "forks" in the code, split
from the trunk and destined to become end-user releases. At conception, a branch contains everything that the trunk contains, but from that point onwards, only certain fixes or changes will be accepted. Therefore, over time, the branch becomes more stable.
• MozillaZine– http://forums.mozillazine.org/viewtopic.php?t
=305281
57CSM CH-57112/04/18
Light-Weight CMMI
Configuration ManagementConfiguration Management
• Use Free Software Tool - CVS– Defining Configuration Items
– Define Access & Maintenance Rules
– Define Baseline Creation, Release, & Change Rules for Version Control
– Record CM activities
Dr. Chaw-Kwei Hung 洪肇奎 , Light-Weight CMMI.