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Posts Tagged ‘spaghetti’

Code bureaucracy can reduce the demand for cognitive resources

March 7, 2021 5 comments

A few weeks ago I discussed why I thought that research code was likely to remain a tangled mess of spaghetti code.

Everybody’s writing, independent of work-place, starts out as a tangled mess of spaghetti code; some people learn to write code in a less cognitively demanding style, and others stick with stream-of-conscious writing.

Why is writing a tangled mess of spaghetti code (sometimes) not cost-effective, and what are the benefits in making a personal investment in learning to write code in another style?

Perhaps the defining characteristic of a tangled mess of spaghetti code is that everything appears to depend on everything else, consequently: working out the impact of a change to some sequence of code requires an understanding of all the other code (to find out what really does depend on what).

When first starting to learn to program, the people who can hold the necessary information on increasing amounts of code in their head are the ones who manage to create running (of sorts) programs; they have the ‘knack’.

The limiting factor for an individual’s software development is the amount of code they can fit in their head, while going about their daily activities. The metric ‘code that can be fitted in a person’s head’ is an easy concept to grasp, but its definition in terms of the cognitive capacity to store, combine and analyse information in long term memory and the episodic memory of earlier work is difficult to pin down. The reason people live a monks existence when single-handedly writing 30-100 KLOC spaghetti programs (the C preprocessor Richard Stallman wrote for gcc is a good example), is that they have to shut out all other calls on their cognitive resources.

Given time, and the opportunity for some trial and error, a newbie programmer who does not shut their non-coding life down can create, say, a 1,000+ LOC program. Things work well enough, what is the problem?

The problems start when the author stops working on the code for long enough for them to forget important dependencies; making changes to the code now causes things to mysteriously stop working. Our not so newbie programmer now has to go through the frustrating and ego-denting experience of reacquainting themselves with how the code fits together.

There are ways of organizing code such that less cognitive resources are needed to work on it, compared to a tangled mess of spaghetti code. Every professional developer has a view on how best to organize code, what they all have in common is a lack of evidence for their performance relative to other possibilities.

Code bureaucracy does not sound like something that anybody would want to add to their program, but it succinctly describes the underlying principle of all the effective organizational techniques for code.

Bureaucracy compartmentalizes code and arranges the compartments into some form of hierarchy. The hoped-for benefit of this bureaucracy is a reduction in the cognitive resources needed to work on the code. Compartmentalization can significantly reduce the amount of a program’s code that a developer needs to keep in their head, when working on some functionality. It is possible for code to be compartmentalized in a way that requires even more cognitive resources to implement some functionality than without the bureaucracy. Figuring out the appropriate bureaucracy is a skill that comes with practice and knowledge of the application domain.

Once a newbie programmer is up and running (i.e., creating programs that work well enough), they often view the code bureaucracy approach as something that does not apply to them (and if they rarely write code, it might not apply to them). Stream of conscious coding works for them, why change?

I have seen people switch to using code bureaucracy for two reasons:

  • peer pressure. They join a group of developers who develop using some form of code bureaucracy, and their boss tells them that this is the way they have to work. In this case there is the added benefit of being able to discuss things with others,
  • multiple experiences of the costs of failure. The costs may come from the failure to scale a program beyond some amount of code, or having to keep investing in learning how previously written programs work.

Code bureaucracy has many layers. At the bottom there is splitting code up into functions/methods, then at the next layer related functions are collected together into files/classes, then the layers become less generally agreed upon (different directories are often involved).

One of the benefits of bureaucracy, from the management perspective, is interchangeability of people. Why would somebody make an investment in code bureaucracy if they were not the one likely to reap the benefit?

A claimed benefit of code bureaucracy is ease of wholesale replacement of one compartment by a new one. My experience, along with the little data I have seen, suggests that major replacement is rare, i.e., this is not a commonly accrued benefit.

Another claimed benefit of code bureaucracy is that it makes programs easier to test. What does ‘easier to test’ mean? I have seen reliable programs built from spaghetti code, and unreliable programs packed with code bureaucracy. A more accurate claim is that it can be unexpectedly costly to test programs built from spaghetti code after they have been changed (because of the greater likelihood of the changes having unexpected consequences). A surprising number of programs built from spaghetti code continue to be used in unmodified form for years, because nobody dare risk the cost of checking that they continue to work as expected after a modification

Modular vs. monolithic programs: a big performance difference

February 28, 2019 2 comments

For a long time now I have been telling people that no experiment has found a situation where the treatment (e.g., use of a technique or tool) produces a performance difference that is larger than the performance difference between the subjects.

The usual results are that differences between people is the source of the largest performance difference, successive runs are the next largest (i.e., people get better with practice), and the smallest performance difference occurs between using/not using the technique or tool.

This is rather disheartening news.

While rummaging through a pile of books I had not looked at in many years, I (re)discovered the paper “An empirical study of the effects of modularity on program modifiability” by Korson and Vaishnavi, in “Empirical Studies of Programmers” (the first one in the series). It’s based on Korson’s 1988 PhD thesis, with the same title.

There were four experiments, involving seven people from industry and nine students, each involving modifying a 900(ish)-line program in some way. There were two versions of each program, they differed in that one was written in a modular form, while the other was monolithic. Subjects were permuted between various combinations of program version/problem, but all problems were solved in the same order.

The performance data (time to complete the task) was published in the paper, so I fitted various regressions models to it (code+data). There is enough information in the data to separate out the effects of modular/monolithic, kind of problem and subject differences. Because all subjects solved problems in the same order, it is not possible to extract the impact of learning on performance.

The modular/monolithic performance difference was around twice as large as the difference between subjects (removing two very poorly performing subjects reduces the difference to 1.5). I’m going to have to change my slides.

Would the performance difference have been so large if all the subjects had been experienced developers? There is not a lot of well written modular code out there, and so experienced developers get lots of practice with spaghetti code. But, even if the performance difference is of the same order as the difference between developers, that is still a very worthwhile difference.

Now there are lots of ways to write a program in modular form, and we don’t know what kind of job Korson did in creating, or locating, his modular programs.

There are also lots of ways of writing a monolithic program, some of them might be easy to modify, others a tangled mess. Were these programs intentionally written as spaghetti code, or was some effort put into making them easy to modify?

The good news from the Korson study is that there appears to be a technique that delivers larger performance improvements than the difference between people (replication needed). We can quibble over how modular a modular program needs to be, and how spaghetti-like a monolithic program has to be.