embracing conway's law
Most of you have heard of "Conway's Law", the pithy observation that the structure of things that people build reflects the social structure of the people that build them. The extent to which there is coordination or cohesion in a system as a whole reflects the extent to which there is coordination or cohesion among the people that make the system. Interfaces between components made by different groups of people are the most fragile pieces. This division goes down to the inner life of programs, too; inside it's all just code, but when a program starts to interface with the outside world we start to see contracts, guarantees, types, documentation, fixed programming or binary interfaces, and indeed faults as well: how many bug reports end up in an accusation that team A was not using team B's API properly?
If you haven't heard of Conway's law before, well, welcome to the club. Inneresting, innit? And so thought I until now; a neat observation with explanatory power. But as aspiring engineers we should look at ways of using these laws to build systems that take advantage of their properties.
in praise of bundling
Most software projects depend on other projects. Using Conway's law, we can restate this to say that most people depend on things built by other people. The Chromium project, for example, depends on many different libraries produced by many different groups of people. But instead of requiring the user to install each of these dependencies, or even requiring the developer that works on Chrome to have them available when building Chrome, Chromium goes a step further and just includes its dependencies in its source repository. (The mechanism by which it does this isn't a direct inclusion, but since it specifies the version of all dependencies and hosts all code on Google-controlled servers, it might as well be.)
Downstream packagers like Fedora bemoan bundling, but they ignore the ways in which it can produce better software at lower cost.
One way bundling can improve software quality is by reducing the algorithmic complexity of product configurations, when expressed as a function of its code and of its dependencies. In Chromium, a project that bundles dependencies, the end product is guaranteed to work at all points in the development cycle because its dependency set is developed as a whole and thus uniquely specified. Any change to a dependency can be directly tested against the end product, and reverted if it causes regressions. This is only possible because dependencies have been pulled into the umbrella of "things the Chromium group is responsible for".
Some dependencies are automatically pulled into Chrome from their upstreams, like V8, and some aren't, like zlib. The difference is essentially social, not technical: the same organization controls V8 and Chrome and so can set the appropriate social expectations and even revert changes to upstream V8 as needed. Of course the goal of the project as a whole has technical components and technical considerations, but they can only be acted on to the extent they are socially reified: without a social organization of the zlib developers into the Chromium development team, Chromium has no business automatically importing zlib code, because the zlib developers aren't testing against Chromium when they make a release. Bundling zlib into Chromium lets the Chromium project buffer the technical artifacts of the zlib developers through the Chromium developers, thus transferring responsibility to Chromium developers as well.
Conway's law predicts that the interfaces between projects made by different groups of people are the gnarliest bits, and anyone that has ever had to maintain compatibility with a wide range of versions of upstream software has the scar tissue to prove it. The extent to which this pain is still present in Chromium is the extent to which Chromium, its dependencies, and the people that make them are not bound tightly enough. For example, making a change to V8 which results in a change to Blink unit tests is a three-step dance: first you commit a change to Blink giving Chromium a heads-up about new results being expected for the particular unit tests, then you commit your V8 change, then you commit a change to Blink marking the new test result as being the expected one. This process takes at least an hour of human interaction time, and about 4 hours of wall-clock time. This pain would go away if V8 were bundled directly into Chromium, as you could make the whole change at once.
forking considered fantastic
"Forking" sometimes gets a bad rap. Let's take the Chromium example again. Blink forked from WebKit a couple years ago, and things have been great in both projects since then. Before the split, the worst parts in WebKit were the abstraction layers that allowed Google and Apple to use the dependencies they wanted (V8 vs JSC, different process models models, some other things). These abstraction layers were the reified software artifacts of the social boundaries between Google and Apple engineers. Now that the social division is gone, the gnarly abstractions are gone too. Neither group of people has to consider whether the other will be OK with any particular change. This eliminates a heavy cognitive burden and allows both projects to move faster.
As a pedestrian counter-example, Guile uses the libltdl library to abstract over the dynamic loaders of different operating systems. (Already you are probably detecting the Conway's law keywords: uses, library, abstract, different.) For years this library has done the wrong thing while trying to do the right thing, ignoring .dylib's but loading .so's on Mac (or vice versa, I can't remember), not being able to specify soversions for dependencies, throwing a stat party every time you load a library because it grovels around for completely vestigial .la files, et cetera. We sent some patches some time ago but the upstream project is completely unmaintained; the patches haven't been accepted, users build with whatever they have on their systems, and though we could try to take over upstream it's a huge asynchronous burden for something that should be simple. There is a whole zoo of concepts we don't need here and Guile would have done better to include libltdl into its source tree, or even to have forgone libltdl and just written our own thing.
Though there are costs to maintaining your own copy of what started as someone else's work, people who yammer on against forks usually fail to recognize their benefits. I think they don't realize that for a project to be technically cohesive, it needs to be socially cohesive as well; anything else is magical thinking.
not-invented-here-syndrome considered swell
Likewise there is an undercurrent of smarmy holier-than-thou moralism in some parts of the programming world. These armchair hackers want you to believe that you are a bad person if you write something new instead of building on what has already been written by someone else. This too is magical thinking that comes from believing in the fictional existence of a first-person plural, that there is one "we" of "humanity" that is making linear progress towards the singularity. Garbage. Conway's law tells you that things made by different people will have different paces, goals, constraints, and idiosyncracies, and the impedance mismatch between you and them can be a real cost.
Sometimes these same armchair hackers will shake their heads and say "yeah, project Y had so much hubris and ignorance that they didn't want to bother understanding what X project does, and they went and implemented their own thing and made all their own mistakes." To which I say, so what? First of all, who are you to judge how other people spend their time? You're not in their shoes and it doesn't affect you, at least not in the way it affects them. An armchair hacker rarely understands the nature of value in an organization (commercial or no). People learn more when they write code than when they use it or even when they read it. When your product has a problem, where will you find the ability to fix it? Will you file a helpless bug report or will you be able to fix it directly? Assuming your software dependencies model some part of your domain, are you sure that their models are adequate for your purpose, with the minimum of useless abstraction? If the answer is "well, I'm sure they know what they're doing" then if your organization survives a few years you are certain to run into difficulties here.
As a much more minor, insignificant, first-person example, I am an OK compiler hacker now. I don't consider myself an expert but I do all right. I got here by making a bunch of mistakes in Guile's compiler. Of course it helps if you get up to speed using other projects like V8 or what-not, but building an organization's value via implementation shouldn't be discounted out-of-hand.
Another point is that when you build on someone else's work, especially if you plan on continuing to have a relationship with them, you are agreeing up-front to a communications tax. For programmers this cost is magnified by the degree to which asynchronous communication disrupts flow. This isn't to say that programmers can't or shouldn't communicate, of course, but it's a cost even in the best case, and a cost that can be avoided by building your own.
When you depend on a project made by a distinct group of people, you will also experience churn or lag drag, depending on whether the dependency changes faster or slower than your project. Depending on LLVM, for example, means devoting part of your team's resources to keeping up with the pace of LLVM development. On the other hand, depending on something more slow-moving can make it more difficult to work with upstream to ensure that the dependency actually suits your use case. Again, both of these drag costs are magnified by the asynchrony of communicating with people that probably don't share your goals.
Finally, for projects that aim to ship to end users, depending on people outside your organization exposes you to risk. When a security-sensitive bug is reported on some library that you use deep in your web stack, who is responsible for fixing it? If you are responsible for the security of a user-facing project, there are definite advantages for knowing who is on the hook for fixing your bug, and knowing that their priorities are your priorities. Though many free software people consider security to be an argument against bundling, I think the track record of consumer browsers like Chrome and Firefox is an argument in favor of giving power to the team that ships the product. (Of course browsers are terrifying security-sensitive piles of steaming C++! But that choice was made already. What I assert here is that they do well at getting security fixes out to users in a timely fashion.)
to use a thing, join its people
I'm not arguing that you as a software developer should never use code written by other people. That is silly and I would appreciate if commenters would refrain from this argument :)
Let's say you have looked at the costs and the benefits and you have decided to, say, build a browser on Chromium. Or re-use pieces of Chromium for your own ends. There are real costs to doing this, but those costs depend on your relationship with the people involved. To minimize your costs, you must somehow join the community of people that make your dependency. By joining yourself to the people that make your dependency, Conway's law predicts that the quality of your product as a whole will improve: there will be fewer abstraction layers as your needs are taken into account to a greater degree, your pace will align with the dependency's pace, and colleagues at Google will review for you because you are reviewing for them. In the case of Opera, for example, I know that they are deeply involved in Blink development, contributing significantly to important areas of the browser that are also used by Chromium. We at Igalia do this too; our most successful customers are those who are able to work the most closely with upstream.
On the other hand, if you don't become part of the community of people that makes something you depend on, don't be surprised when things break and you are left holding both pieces. How many times have you heard someone complain the "project A removed an API I was using"? Maybe upstream didn't know you were using it. Maybe they knew about it, but you were not a user group they cared about; to them, you had no skin in the game.
Foundations that govern software projects are an anti-pattern in many ways, but they are sometimes necessary, born from the need for mutually competing organizations to collaborate on a single project. Sometimes the answer for how to be able to depend on technical work from others is to codify your social relationship.
One note before opening the comment flood: I know. You can't control everything. You can't be responsible for everything. One way out of the mess is just to give up, cross your fingers, and hope for the best. Sure. Fine. But know that there is no magical first-person-plural; Conway's law will apply to you and the things you build. Know what you're actually getting when you depend on other peoples' work, and know what you are paying for it. One way or another, pay for it you must.