The benefits of not lingering in eddies, and of learning from your own mistakes

I recently watched the CppCon 2014 talk by John “JT” Thomas:
“Embarcadero Case Study: Bringing CLANG/LLVM to Windows”


The presentation brought a few things to mind about which I have opinions :)

Don’t let upstream get away from you

If you’re going to build upon a codebase that you don’t own, a codebase that others are adding enhancements to, where those enhancements are visible to your customers and are available to your competitors — why would you do anything but keep as close as possible to that upstream development?

“JT” argues in favor of following upstream more closely than they did. I’ve read [it seems like] many articles that insist that the only sane way to do Linux kernel driver development is the same — at least if you ever want your changes to be merged, or you want them to be maintainable into the future.

Playing catch-up is hard work, not made easier when upstream is highly active (as is the case for LLVM/clang or the Linux kernel). Investing developer time into regularly integrating changes from upstream is far more palatable than the epic upheaval that comes from chasing major releases.

It seems like regularly integrating has some tangible benefits:

You get the new features as soon as possible. (Also, you get the new bugs. This is software development.)

More manageable schedules. Regular integration will be far more predictable in terms of the time it takes to adapt your branch. There is a limit to how much change can happen upstream at one time. Smaller, regular changes are more predictable, and less likely to cause huge timesinks for programmers i.e. it’s better from a project management perspective.

Reveal conflicts closer their source — it’s better to fix code recently written than having to rewrite it months later.

And, if you’re doing it from the outset, it means the team can become comfortable with that workflow, and develop the skills and judgement to maintain it. Trying to learn those skills after working in a stable branch/dreamworld is only going to increase the friction when the change takes place.

Consider the full cost of contractors

Don’t pay someone outside of your team to develop intimate knowledge about your systems — you’ll need to pay for it again when members of the team have to learn how to maintain and extend those systems at some point in the future.

This is partial text from a slide at around 50:50 in the presentation:

Initial contract work led to slow integration

  • Core compiler team took time out to integrate and get up to speed
  • This type of initial work would have been best done in house or with much closer interaction

Using contractors to add features to your software comes at a cost to the team: no one on the team will know what the contractor learned while completing the task — not the way that the contractor does. No one will have full insight into why decisions were made the way that they were. If you want your team to be able to support the code after the contractor is finished, you’ll need to set aside more time to develop familiarity.

In many cases, it’s better to kill two birds with one stone: let someone familiar with your codebase do the work of learning about the new area. You’ll keep the expert knowledge on the team, and any newly written code will have a better chance of fitting in with existing standards and practices of the codebase.

If it’s something that you expect to be using and maintaining into the future, keep it in-house. Or expect to keep paying the contractor, and plan for the cost of poorly integrated code.

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