Code Co-op

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Code Co-op

Latest release	5.0 / Nov 15, 2006
OS	Windows
Available in	English
Type	version control system
License	commercial
Website	Reliable Software

Code Co-op is the peer-to-peer version control system made by Reliable Software.

1 Distinguishing features
2 Standard features
3 History
4 Challenges
5 Theoretical Foundations
- 5.1 Bibliography
6 External links

Distinguishing features

Code Co-op is a distributed version control system of the closed type.

It uses peer-to-peer architecture to share projects among developers and to control changes to files. Instead of using a centralized database (the repository), it replicates its own database on each computer involved in the project.

The replicas are synchronized by the exchange of (differential) scripts. The exchange of scripts may proceed using different transports, including e-mail (support for SMTP and POP3, integration with MAPI clients, Gmail) and LAN.

Code Co-op has a built-in Peer-to-peer wiki system, which can be used to integrate documentation with a software project. It's also possible to create text-based Wiki databases, which can be queried using simplified SQL directly from wiki pages.

Standard features

Distributed development support through E-mail, LAN, or VPN
Change-based model—modifications to multiple files are checked in as one transaction
File additions, deletions, renames, and moves are treated on the same level as edits—they can be added in any combination to a check-in changeset
File changes can be reviewed before a check-in using a built-in or user-defined differ
Synchronization changes can be reviewed in the same manner by the recipients
Three-way visual merge
Project history is replicated on each machine. Historical version can be reviewed, compared, or restored
Integration with Microsoft SCC clients, including Visual Studio

History

Code Co-op was the first distributed version control system. It debuted at the 7th Workshop on System Configuration Management in May 1997 [1].

The development of Code Co-op started in 1996, when Reliable Software, the distributed software company that makes it, was established. Reliable Software needed a collaboration tool that would work between the United States and Poland. The only dependable and affordable means of communication between the two countries was e-mail, hence the idea of using e-mail for the exchange of diffs. Of course, with such slow transport, using a centralized repository was unfeasible. Each user of Code Co-op had to have a full replica of the repository, including the history of changes.

The problem was reduced to that of designing a distributed database that uses slow and unreliable transport for synchronization (later, faster LAN transport was also added). It also followed that the synchronization between multiple sites must use some kind of peer-to-peer protocol.

Challenges

The biggest challenge for a distributed system is the merge problem—How to create a single "official" version of the project from contributions made by many independent developers?

In a centralized version control system, it's the server that keeps the official copy of the project—the central repository. All changes are made against the trunk version stored in that repository. Conflicts are avoided by providing a centralized locking mechanism. The server is locked during each individual check-in operation.

In a distributed system, each project member works on his or her private copy of the project, and check-ins are made into a local repository. In open distributed systems each user works on their respective branch, which has to be manually merged into the trunk at some point. A closed system, like Code Co-op, creates instead the illusion of a single trunk against which all check-ins are done. This alleviates the need for frequent merges.

Theoretical Foundations

Code Co-op is an example of a distributed database. Local repositories are considered the replicas of this virtual database. Each check-in corresponds to a distributed commit—a non-blocking version of a Two-phase commit.

Bibliography

Philip A. Bernstein, Vassos Hadzilacos, Nathan Goodman, "Concurrency Control and Recovery in Database Systems", Chapter 7, Distributed Recovery
Bartosz Milewski, "Distributed Source Control System", in Raidar Conradi, ed., Software Configuration Management, ICSE'97 SCM-7 Workshop, Proceedings, Springer 1997