Tips on Managing Concurrent Development?

An Anonymous Coward queries: "I work on a fairly large-sized project with at least a dozen developers. Advanced tools like CVS and ClearCase allow concurrent development, and provide merging tools to merge in different changes to the same file. This can be a significant productivity gain, particularly with files that are unavoidably common to several developers (C header files, most notoriously). During crunch times, such as before delivery deadlines, we often find that we are checking in changes to the same file several times a day, often hourly. The problem does not seem to be with conflicting changes to the same lines of code, but rather with developers knowing the sequence in which concurrent changes will be checked in. It is not possible to always be aware of who is checking in what and when, so programmers submitting patches to the baseline often have to redo those patches multiple times in a day in order to have them applied. Have other programming projects developed solutions for dealing with this problem?" The submitter proposes another solution, below, how well would it work?

"Take, for example, the extreme case of something like Linux (not only concurrent development, but geographically distributed development), how is this managed? One solution we were contemplating was to try to do an 'air traffic control' type of sequencing and conflict resolution. As early as possible in the development stage, we try to identify what will be finished when, and assign a one-up sequence number to each patch. Developers then know that they will be patching against the baseline that was patched by the patch with the previous sequence number. It is hoped that this prevents a lot of rework of patches. A potential problem with this approach is the need for a responsive central authority to assign sequence numbers. Also, such sequence numbers may have to be rearranged in the face of last minute advances and setbacks in developer progress. Despite careful scheduling and detailed design, it may be impossible to know the exact check-in sequence of patches more than a week or two in advance.

Will such an idea be successful, or is it fatally flawed? Are there better solutions to the problem with less effort? Are we treating symptoms and not the disease (i.e., should we be planning better so that we know patch sequences and dependencies early on)? Management likes to keep staff productively occupied and working up until deadlines, so this usually means a lot of checkins within a short period of time, rather than staged checkins. Can checkins be spread out over time while keeping developers productively occupied?"

Comments

SourceForge 3.0 Enterprise Edition

[Anonymous Coward]

(disclaimer: I am a VA Software employee)

I know this sounds corny, being said on a VA property such as Slashdot, but SourceForge 3.0 is easily the best concurrent development environment i have ever used. It was my love for Sourceforge which made me pursue a job at VA Software in the first place! The fully web-based administration hides all the niggling details of commandline cvs tools and makes managing huge projects a piece of cake.

In short, if you haven't been to VA Software's site, you don't know what you're missing.

Re:SourceForge 3.0 Enterprise Edition

[sourcehunter]

Problem with SF EE:

Minimum user license is 30 users, and that is roughly $30,000!!!

I run a small development firm and I wanted to use the enterprise edition. I'll pay a few thousand for something, but $30k for 30 people? I think not.

Better Solution: Use CVS or ClearCase Properly!

[noahbagels]

I currently work in an organization with 75 Engineers (50 USA, 20 India, 5 Asia) - and we use CVS. It's free, easy to use, and has a simple feature set so that more than one person has enough knowledge to do things like branching and merging branches.

We nearly never have merge problems. It is standard procedure that people keep their tree up-to-date with the cvs tree, and thus conflicts rarely arrise. Even at crunch-time, I probably have one merge conflict every 2 weeks, and with CVS - you are notified of the conflict and it is wrapped with CVS comments.

To put this in perspective - while at Oracle with 1000s of engineers working on the same tree, we used ClearCase and it was awesome. The difference here is that there was much steeper a learning curve, and no normal engineers could actually do complex tasks - i.e. create branches etc. We had a complete groud dedicated to ClearCase.


Conclusion:
Educate your engineers - and politely have the senior engineers tell them when they mess up - enforce a policy that people must update the source every day that they plan on checking-in files.

Also - I don't know what CVS versio you are using, but the latest free WinCVS client will not allow you to check in a file with a conflict! It will force you to update/merge/resolve the conflict before updating the tree. I highly recommend CVS and WinCVS due to the ease of use and cost.

Re:Better Solution: Use CVS or ClearCase Properly!

[PD]

We nearly never have merge problems. It is standard procedure that people keep their tree up-to-date with the cvs tree, and thus conflicts rarely arrise

I'll second this: At many companies I have heard over and over that CVS sucks because of the conflicts. When I inquire further, I find out that people never or rarely use the cvs update command to synchronize. cvs update should be executed almost like a nervous habit, or at least a couple times a day. More if code is being checked in frequently, or if you are working on the same code as someone else. Use the watch commands in cvs to be notified when others edit your files.

It's a shame, really, because programmers seem to be afraid of cvs, preferring a more primitive tool such as rcs or pvcs. cvs lets programmers work in the style that is most natural in an open-source arrangement, and in my opinion can be a far more productive environment than a systems that locks the rest of the team out of critical files.

Use Continuous Integration

[rimsky]

One solution to avoid patching problem is to use continuous integration. It's an integration technique that builds your source multiple times a day, getting all the latest source code from the CVS tree, and building from that code. If anything fails, the offending developer gets warned. Mozilla uses the same thing, calling it TinderBox. It's one of the principles of Extreme Programming, and seems to work quite well at our company.

Source Control + Automated Build & Test

[spullara]

These are the ingredients to make large projects successful from a technical point of view. At the company I work for, we have literally hundreds of people working in the same source tree using P4. It manages merges, versioning, and works flawlessly over the internet (well VPN anyway). It is also much, much faster at syncing to the the depot than CVS because the server keeps track of those files that you are editing and does not need to do diffs with the local filesystem. This is very helpful during crunchtime where you might want to sync serveral times a day (and you have about 10000 files in the system). Also, until your locally edited files are resolved with changes in the depot you cannot submit them, so you don't have the problem of ordering patches properly.

For the second part, I highly reccommend that you have automated build and tests that run after changes have been submitted. You can see how this is done en mass on the mozilla.org site. Also, developers should have access to the same build and test infrastructure on their machines so they can do the build and test before they check in their code.

Finally, you need a good bug tracking system. You might try Bugzilla.

Good luck,
Sam

On CVS and Clearcase

[ajs]

I've admined both extensively, and I can make a couple of comments here. First, Clearcase is licensed software. Understand that when you get locked out because all of the licenses are in use, you cannot touch your source-code (though someone with a license can copy it into a sandbox for you). Also, Clearcase is a resource pig. It wants a pretty beefy central machine to run on, and if lots of people compile at the same time, the virtual filesystem is not very efficient.

Now on to CVS. CVS is most everything you want from revision control. It's biggest shortcomings are in branch management and the ease with which changes can be made incorrectly. Its ability to interface with well known and standard protocols like rsh, ssh and gzip (which is a format more than a protocol) make it painful to move to anything that's overly proprietary. Its use of your local diff is wonderful ("cvs diff -u" was a revelation for me).

Clearcase manages branches better and can handle non-realtime latency in updates (e.g. you can have two Clearcase repositories at different sites and you can connect them by mailing tapes around or by dialing up once a day). This can be invaluable when you're working in high-security environments, but is otherwise mostly a moot point.

Clearcase has improved in the last few years. They've added some local-checkout features where you don't have to work off of the virtual filesystem, and that helps.

Overall, I'd say CVS is the better system, but Clearcase will sometimes get jammed down your throat, and there are definitely worse fates than to have to get your project working under it.

Perforce and process recommendation

[enkidu]

Disclaimer: I not an employee of Perforce. I used to be a ClearCase weanie, but now that I've been using Perforce for about a year and a half, I think it's better for several reasons:

• Smaller. You only need one executable on your client. And one more for your server. No kernel patches, no drivers, no installation, just the binaries. Ubercool.
• Multi-platform. Perforce has binaries for practically every platform in use out there. Find me another Version Control System with BeOS, QNX, AIX, SCO, MacOS9 and MacOSX support.
• Fast, fast fast. Because of the low communication overhead, it works extremely well across slow/high latency links.
• Ease of use. It's really easy to configure and setup.
• Great support. We've had to go to perforce support twice and both times they've been awesome, with quick responses and knowledgeable people.
• Price. The single server, two client setup is FREE! And per seat licensing + support is very very reasonable. I use the free one on my laptop to version files.
• Plug-ins. Perforce publishes their API, and they have perl, python, ruby and tcl utilities galore.

Now my process recommendation. If you have paid for ClearCase then pay for some more education. ClearCase/Perforce can do lots of what you need automatically. You should practically NEVER have to repeat the same change on a file. You may want to look at some branching/merging techniques which can eliminate the need for colliding checkin's also. Rational has a bunch of whitepapers up on their site, as does Perforce.

Most of all, I would advise you to educate yourself on the options/methods of version control. 12 isn't that big. Wait 'til you get to 1200.

Make developers mere on checkin

[SuperKendall]

I have used both CVS, Clearcase, MKS, straight RCS, and a bit of Visual Source-Safe (Ha!).

What I have found makes the most difference in reducing merge issues is (1), have developers merge on checkin (more on that in a moment), and (2) develop a branching strategy that reduces the need to merge.

On (1). When using ClearCase, have people set checkouts to be "unreserved". When they check out a file it won't lock it so everyone else can use it, and when they check something in ClearCase will force them to perform a merge if it has been updated since they checked it out. Make everyone learn how to use the henious merge tool. Also (and I'm not sure if this is fixed now or if I never figured out how to configure this right) I have had major issues with EOL markers in files and clearcase merge - if a developer edits a file that changes the EOL character(s), then ClearCase merge will claim the whole file differs.

For CVS, it pretty much works naturally the way a system should - the default is to check out something "unreserved" (or at least that's how I remember it!). You can either update a file while you're making changes to keep up to date an make merges smaller, or just wait until you're done - before you can check it in CVS will make you update the file and merge your changes.

In both systems, an approach of having the developer merge the file means the person who really knows what's going on can resolve any conflicts with the merge. Most merges are automatically handled and so often no work is required. I'm not sure how much this really addresses your issue, but it can't hurt to rely more on the source control system helping you manage merges.

For option (2), think carefully about how you want to structure releases. One approach I've used before is having dfferent "levels" of development - you have a production branch, fix branch, development 1, dev 2, etc. You start out code at some given level (say development 2) and as it is completed and tested it moves up through the ranks until it reaches the production level. That worked pretty well and meant a fixed number of branches.

In more recent projects I've been working with a monthly release structure - each months release requires a new branch. This was not my idea, believe me... it might seem nice in theory but in practice you might have three or more months of development at the same time. This leads to something of a merging cross-nightmare. Some sort of branching structure might well help solve your problem, if only in thinking up how you can more clearly seperate changes to a file or set of files.

Re:Subversion!

[big_hairy_mama]

As early as possible in the development stage, we try to identify what will be finished when, and assign a one-up sequence number to each patch. Developers then know that they will be patching against the baseline that was patched by the patch with the previous sequence number. It is hoped that this prevents a lot of rework of patches. A potential problem with this approach is the need for a responsive central authority to assign sequence numbers. Also, such sequence numbers may have to be rearranged in the face of last minute advances and setbacks in developer progress. Despite careful scheduling and detailed design, it may be impossible to know the exact check-in sequence of patches more than a week or two in advance.

When Subversion is ready, you might check it out. It keeps track of not specific versions for files, but revisions/patches for the entire tree. This way you can tell exactly the state of all the code at, say, revision 2735. No manual tagging needed. This would take up a lot of the work of your sequence numbers, without the severe administrative overhead. You could even try to assign a range of actual revisions for which a specific feature is targetted.

I'm already using Subversion for the early stages of one of my projects. It seems to be very stable currently, and of course I still make backups of the DB in case there still remain bugs that would corrupt it. I figure, I won't need to make any branches or merges in this project until well after the time that subversion can support it (due in April).

I've found in my experience...

[joto]

...that the best solution to this problem is that your fellow developers are in an office across the hall, and that you can walk into their office and talk to them about the changes.

But that doesn't scale... So you've got to modularize the project so that each team works against their own baseline. Any changes that you do to another teams part, must be given to them, for them to check out, and integrate themselves. The important thing is communication, it often happens that they are working on fixing the same problem, but in another and better way, and can give you back their fix instead.

So when you're having problems with your revision control system, what you are really experiencing most of the time, is problems with communication.

Ideally, all developers should be in the same building, they should work at (mostly) the same time (normal office hours), and they should all be friends, and keep a list of each others telephone-numbers, and eat lunch at the same time. Development should be split into projects (having 10-50 people on each project) that are mosty independent. All the people on the project should meet weekly, and discuss their project, important changes, etc... On each project there can be one or more teams, each consisting of four to eight people, who should have offices really close to each other. On each team, development should be split into sub-teams, consisting of 1-3 persons (depending on difficulty and experience), who should share an office, and thus communicate even further. And just as important: this should not be formalized (at least not too much). People should rotate around somewhat, not being stuck with the same people all the time, to get them to know other parts of the project, and other people to communicte with.

The important lesson I am trying to give is that the most beneficial communication, is often the informal. While having a tool help you with managing deltas is surely helpful, it can't solve every problem in the world. You need to work together, but you also need to modularize, and most importantly, you all need to be friends...