Version Control with Subversion

Version Control with Subversion

Speaker: Chen-Nien TsaiAdviser: Kai-Wei KeDate: 2006.01.17

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Outline• Introduction• Basic Concepts

– Repository– Versioning Models

• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion

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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.

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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.

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Outline• Introduction• Basic Concepts

– Repository– Versioning Models

• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion

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Repository (1/2)• Subversion is a centralized system

for sharing information.• A repository is a central store of

data.

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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.

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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.

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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.

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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

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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

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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

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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.

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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.

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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

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Sally publishes her version first

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Harry gets an out-of-date error

Out-of-date

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Harry compares the latest version to his own

Merging

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A new merged version is created

A miracle?

Even a conflict occur?

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The merged version is published

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Now both users have each other’s changes

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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.

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Outline• Introduction• Basic Concepts

– Repository– Versioning Models

• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion

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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

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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.

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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.

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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.

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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>.

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Outline• Introduction• Basic Concepts

– Repository– Versioning Models

• Basic Work Cycle• Branch, tag, and Merging• Resources• Conclusion

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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.

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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.

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Branches

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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.

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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”

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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.

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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.

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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/

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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

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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.

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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

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Resources• Other Browser interfaces

– Easy SVN Browser– WebSVN– SVN::Web

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We all have our time machines. Some take us back, they're called memories.

Some carry us forward, they're called dreams.

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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

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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-57112/04/21

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.