standards

Are We Smart Enough to Use Kind Words?

My title might seem oddly out of place on a tech blog, but a slashdot post today led me to an email thread for linux kernel developers, and the thread and its fallout leave me troubled.

Apparently, a veteran contributor is leaving the kernel dev community because she feels like the communication style there is too harsh. This is unfortunate, but what seems even more lamentable to me is the lack of sympathy in Linus Torvalds’ reaction. It seems to me that his attitude is: “That’s just the way us kernel devs are, and we aren’t going to change to accommodate anybody. If you can’t take the heat, get out of the kitchen.”

This feels sad to me. Kind words can be such a joy.

Secret 3
[Image credit: Glen J. Photography (Flickr)]

Linus is a brilliant guy, and I’m grateful to him. I use linux and git every day; the tools he’s built do a lot of good in the world, and they replace earlier approaches that are clearly inferior. I also agree with his complaint that an explicit standard of “professionalism” in communication can, in some cases, lead to opacity, disingenuousness, and inefficiency. Sometimes we need to say things that are difficult for others to hear, and we need to say them quickly–and that may not jibe with the communication style of a slick politician.

However, I find it ironic that a profession so passionate about message passing and interfaces and producer/consumer contracts could lightly dismiss communication concerns when they involve humans. Do the messes created by DDoS, attackers probing vulnerabilities, and poorly behaved clients teach us nothing?

We certainly need clarity in our careers, and we may occasionally need bluntness as well, but we don’t need ridicule, sarcasm, or disdain. I applaud the sentiments of Marvin J. Ashton:

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How Sutter’s Wrong About const in C++ 11

Herb Sutter recently gave a talk about how the const keyword and the mutable keyword have subtle but profoundly different semantics in C++ 11. In a nutshell, he says that C++ 11 corrects the wishy-washy definition of const in C++ 98; const used to mean “logically constant,” but now it means thread-safe. And mutable now means thread-safe as well. His summary slide says:

const == mutable == thread safe (bitwise const or internally synchronized)

Editor’s note: Since this post was written, Herb has updated his slide. See Herb’s note in the comment stream below.

Now, I think Herb’s talk is quite informative, and I don’t dispute the core of what he was trying to convey. It’s a good insight, well worth the community’s attention. I learned something important; I recommend that you watch the talk. Using const well is an essential skill. But I think in his enthusiasm about the way the language has evolved to make semantics clearer, Herb does us a disservice by oversimplifying.

When Herb uses the C++ == operator to boil his point down to a pithy summary, he’s implying true equivalence; what’s on one side of the operator is, for all intents and purposes, identical to or indistinguishable from what’s on the other side. And while const and mutable and thread-safe are highly related concepts, they are not equivalent enough to each other for ==.

To understand why, answer the following question: Why would good code use const and/or mutable even if it’s single-threaded?

Ah. I imagine you nodding your head sagely. You see where I’m going, don’t you?

These two keywords don’t just define semantics for cross-thread access; they define the semantics a variable or object supports when accessed by various scopes (e.g., subroutines or code blocks) on the same thread. If you pass a const Widget & to a function, that function can’t call Widget::modifyState() even if it’s the only thread in the universe. If you declare a m_lazy_init member variable to be mutable, you are telling the compiler to let you change it where it would normally be disallowed, including on the same thread.

So: const means unchangeable in whatever scope sees const (including many threads), which is why it also implies thread-safe (if all threads see const); mutable means changing safely in one or many threads, which is why it also implies thread-safe (if all threads see const). In C++ 98, these semantics were a bit loose. You could use them carelessly, cast away parts of their guarantees, and generally operate as a law unto yourself. In C++ 11 the semantics of const and mutable are explicit and exacting; the standard library demands thread-safe copy construction. As a result, their role in thread safety is clarified, and we all write better code. Mutexes and atomics and certain kinds of queues are inherently safe to change from any thread; they deserve and require the mutable keyword.

Instead of Herb’s final equation, I’d propose a Venn diagram:

The const and mutable keywords are not equivalent in C++ 11, but they do share guarantees about thread safety.

The const and mutable keywords are not equivalent in C++ 11, but they do share guarantees about thread safety.

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// Comments on Comments

/*

We spend little or no time teaching programmers how to write good comments.

This is surprising, when you consider how often “total lack of comments” or “poor comments” are cited as evidence that certain modules (or the programmer who wrote them) are the worst thing that ever happened to the technoverse.

Comments shouldn’t leave you–or anybody else–mystified. :-) Image credit: xkcd

I happen to think that there are much yuckier tech things than poor or missing comments in code. But I still think our general level of comment proficiency is lower than it should be.

Here is my attempt to raise the bar a little.

Why We Comment

Sooner or later, most interesting programming problems require a sophisticated mental model of a problem. Building these models is hard work, and once we have them, we are paid to share with our team (or our future selves).

The best way to share mental models with other engineers is Continue reading →

How to turn coding standards into epic fails — or not

Yes, a restaurant really displayed this sign. I doubt it influenced anybody’s behavior…

Some attempts to influence the behavior of other people succeed; others are doomed from the get-go.

Coding standards are usually written because we want to influence the structure or style of code produced by engineering teams. Sometimes they’re helpful; more often they’re ignored and forgotten; occasionally they provoke fireworks or bitter resentment.

I’m not sure there’s a guaranteed formula for success, but there’s a guaranteed formula for failure; let’s cover that first, and then see what helpful suggestions we can derive.

How to turn coding standards into epic fails

1. Micromanage.

Leave no room for personal style and creativity. Make no attempt to distinguish between meaty issues and utter trivialities. State all rules in absolutes; allow no exceptions. Announce enforcement in code reviews. Bonus points if you actually follow through on the threat, and double bonus points if you display some other developer’s code in front of the team as an example of egregious violations.

“Always put a space between an identifier and a curly brace, except in nested struct initializers where the first member is a string literal (other than NULL) or a #define’ed constant.”

“Begin every function with a comment that specifies the name of the coder, the date the function was last modified, the purpose of the function, an annotated history of how the function has evolved over time, a list of functions called by your function, your zodiac sign, and the names of all parameters. Make sure that parameters are listed alphabetically (case-insensitive), with a blank line between each, and the explanatory text after the param name indented 8 – (len(param name) mod 4) spaces.”

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