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Posts Tagged ‘culture’

Open source: monoculture is more desirable than portability

March 8th, 2014 No comments

An oft repeated fable is that open source software is portable, all thanks to C and Unix. The reality is that open source lives in an environment that is evolving to become a monoculture that does not require portability, this is being driven by the law of the jungle.

First some background and history. Portability requires that source code have the same behavior on different platforms, or rather than programs built from that code have the same behavior, this requires that:

  • all compilers assign the same semantics to a given piece of code,
  • all operating systems include support the same set of libraries in the same way.

If you want portability across lots of compilers then Fortran has stood head and shoulders above the competition for decades. Now some C folk may point out that they have been compiling some large code base for decades, with few changes necessitated by compiler differences; yes this has been possible in certain niche markets where there is a dominant supplier who has a vested interest in not breaking customer code. C has a long history of widespread large variation in behavior of across compilers.

What about Cobol you ask? Cobol is all about data manipulation and unless you have data in the format expected by a Cobol program you have no need for that program. Nobody cares about portable Cobol programs unless they are also interested in portable data.

If you want portability across lots of operating systems the solution has always been to minimise the dependency on system/third-party library calls (to the extent of including source code for functionality often supported by an OS). The reason for minimising OS dependency is the huge variation in support for different libraries and a wide range of behaviors for supposedly the same functionality. But you say, Unix is an OS that did/does provide a common set of libraries that have the same behavior; no, this is history seen through rose tinted glasses as anyone who knows about the Unix wars will tell you.

In the last century, to experience ‘portability’ Unix developers had to live in a monoculture of either PDP-11s or Sun workstations.

Open source, as it existed in the 1970s, 80s and into the 90’s was Fortran code that ran on a surprisingly wide range of OS/cpu/compilers, along with a smattering of other languages. Back then there were not many software applications and when they did exist many were written in Fortran (Oracle being an early, lots of Fortran, example), this created a strong incentive for vendors to support a Fortran compiler that did things the same way as everybody else (which did not prevent them adding proprietary goodies to try and lure customers towards lock-in).

How did we get to today’s dominance of C and Unix? Easy, evolution at a rate that caused competitors to die out until there was a last man standing. That last man standing was gcc and Linux. The portability problem has been solved by removing the need to port code; it is compiled by the same compiler to run on the same cpu (Intel x86 family) to run under the same OS (Linux).

Of course some of today’s open source C is compiled using non-gcc compilers, but the percentage is small and specialised (a lot of the older code is portable because it used to exist in a multi-compiler/cpu/OS world and had to evolve into being portable). The gcc competitor, llvm, is working long and hard to ensure compatibility and somehow has to differentiate itself while being compatible, a tough fight for developer hearts and minds.

Differences in CPU characteristics are a big headache to any compiler writer wanting to support identical behavior across platforms; having a single cpu family as the market leader more or less solves this problem. ARM has become a major player in the CPU world, but it shares many developer visible characteristics with Intel x86 (e.g., 32-bit int, 64-bit long, pointer and ints are the same size and IEEE floating-point) and options are available for handling some of the other potential differences (e.g., right shift of signed integers).

The Unix wars have not gone away, they have moved to more far flung battlefields leaving behind some hard fought over common ground. Anybody who wants to see the scares left by these war only needs to look at the #ifs in system headers or the parameters selected inside .configure files.

Having everybody use the same compiler/cpu/OS saves having to make a huge time/money investment in making software portable, at least until the invention of photonic computers or the arrival of aliens (whose computers are unlikely to contain a CPU that shares Intel/ARM characteristics or have the same libraries as Linux).

C/Linux has not won in the sense that competitors have given up; in 20 years time the majority of open source in active use might be Javascript running inside a browser.

Push hard on a problem here and it might just pop up over there

April 2nd, 2013 7 comments

One thing I have noticed when reading other peoples’ R code is that their functions are often a lot longer than mine. Writing overly long functions is a common novice programmer mistake, but the code I am reading does not look like it is written by novices (based on the wide variety of base functions they are using, something a novice is unlikely to do, and by extrapolating my knowledge of novice behavior in other languages to R). I have a possible explanation for these longer functions, R users’ cultural belief that use of global variables is taboo.

Where did this belief originate? I think it can be traced back to the designers of R being paid up members of the functional programming movement of the early 80’s. This movement sought to mathematically prove programs correct but had to deal with the limitation that existing mathematical techniques were not really up to handling programs that contained states (e.g., variables that were assigned different values at different points in their execution). The solution was to invent a class of programming languages, functional languages, that did not provide any mechanisms for creating states (i.e., no global or local variables) and using such languages was touted as the solution to buggy code. The first half of the 80’s was full of computing PhD students implementing functional languages that had been designed by their supervisor, with the single application written by nearly all these languages being their own compiler.

Having to use a purely functional language to solve nontrivial problems proved to be mindbogglingly hard and support for local variables crept in and reading/writing files (which hold state) and of course global variables (but you must not use them because that would generate a side-effect; pointing to a use of a global variable in some postgrad’s code would result in agitated arm waving and references to a technique described in so-and-so’s paper which justified this particular use).

The functional world has moved on, or to be exact mathematical formalisms not exist that are capable of handling programs that have state. Modern users of functional languages don’t have any hangup about using global variables. The R community is something of a colonial outpost hanging on to views from a homeland of many years ago.

Isn’t the use of global variables recommended against in other languages? Yes and No. Many languages have different kinds of global variables, such as private and public (terms vary between languages); it is the use of public globals that may raise eyebrows, it may be ok to use them in certain ways but not others. The discussion in other languages revolves around higher level issues like information hiding and controlled access, ideas that R does not really have the language constructs to support (because R programs tend to be short there is rarely a need for such constructs).

Lets reformulate the question: “Is the use of global variables in R bad practice?”

The real question is: Given two programs, having identical external behavior, one that uses global variables and one that does not use global variables, which one will have the lowest economic cost? Economic cost here includes the time needed to figure out how to write the code and time to fix any bugs.

I am not aware of any empirical evidence, in any language, that answers this question (if you know of any please let me know). Any analysis of this question requires enumerating those problems where a solution involving a global variable might be thought to be worthwhile and comparing the global/nonglobal code; I know of a few snippets of such analysis in other languages.

Coming back to these long R functions, they often contain several for loops. Why are developers using for loops rather than the *ply functions? Is it because the *aply solution might require the use of a global variable, a cultural taboo that can be avoided by having everything in one function and using a for loop?

Next time somebody tells you that using global variables is bad practice you should ask for some evidence that backs that statement up.

I’m not saying that the use of global variables is good or bad, but that the issue is a complicated one. Enforcing a ‘no globals’ policy might just be moving the problem it was intended to solve to another place (inside long functions).

Using identifier prefixes results in more developer errors

April 25th, 2012 1 comment

Human speech communication has to be processed in real time using a cpu with a very low clock rate (i.e., the human brain whose neurons fire at rates between 10-100 Hz). Biological evolution has mitigated the clock rate problem by producing a brain with parallel processing capabilities and cultural evolution has chipped in by organizing the information content of languages to take account of the brains strengths and weaknesses. Words provide a good example of the way information content can be structured to be handled by a very slow processor/memory system, e.g., 85% of English words start with a strong syllable (for more details search for initial in this detailed analysis of human word processing).

Given that the start of a word plays an important role as an information retrieval key we would expect the code reading performance of software developers to be affected by whether the identifiers they see all start with the same letter sequence or all started with different letter sequences. For instance, developers would be expected to make fewer errors or work quicker when reading the visually contiguous sequence consoleStr, startStr, memoryStr and lineStr, compared to say strConsole, strStart, strMemory and strLine.

An experiment I ran at the 2011 ACCU conference provided the first empirical evidence of the letter prefix effect that I am aware of. Subjects were asked to remember a list of four assignment statements, each having the form id=constant;, perform an unrelated task for a short period of time and then recall information about the previously seen constants (e.g., their value and which variable they were assigned to).

During recall subjects saw a list of five identifiers and one of the questions asked was which identifier was not in the previously seen list? When the list of identifiers started with different letters (e.g., cat, mat, hat, pat and bat) the error rate was 2.6% and when the identifiers all started with the same letter (e.g., pin, pat, pod, peg, and pen) the error rate was 5.9% (the standard deviation was 4.5% and 6.8% respectively, but ANOVA p-value was 0.038). Having identifiers share the same initial letter appears to double the error rate.

This looks like great news; empirical evidence of software developer behavior following the predictions of a model of human human speech/reading processing. A similar experiment was run in 2006, this asked subjects to remember a list of three assignment statements and they had to select the ‘not seen’ identifier from a list of four possibilities. An analysis of the results did not find any statistically significant difference in performance for the same/different first letter manipulation.

The 2011/2006 experiments throw up lots of questions, including: does the sharing a prefix only make a difference to performance when there are four or more identifiers, how does the error rate change as the number of identifiers increases, how does the error rate change as the number of letters in the identifier change, would the effect be seen for a list of three identifiers if there was a longer period between seeing the information and having to recall it, would the effect be greater if the shared prefix contained more than one letter?

Don’t expect answers to appear quickly. Experimenting using people as subjects is a slow, labour intensive process and software developers don’t always answer the question that you think they are answering. If anybody is interested in replicating the 2011 experiment the tools needed to generate the question sheets are available for download.

For many years I have strongly recommended that developers don’t prefix a set of identifiers sharing some attribute with a common letter sequence (its great to finally have some experimental backup, however small). If it is considered important that an attribute be visible in an identifiers spelling put it at the end of the identifier.

See you all at the ACCU conference tomorrow and don’t forget to bring a pen/pencil. I have only printed 40 experiment booklets, first come first served.

The changing shape of code in the next decade

December 29th, 2009 No comments

I think there are two forces that will have a major impact on the shape of code in the next decade:

  • Asian developers. China and India each have a population that is more than twice as large as Europe and the US combined, and software development has been kick started in these countries by a significant amount of IT out sourcing. I have one comparative data point for software developers who might be of the hacker ilk. A discussion of my C book on a Chinese blog resulted in a download volume that was 50% of the size of the one that occurred when the book appeared as a news item on Slashdot.
  • Scripting languages. Software is written to solve a problem and there are only so many packaged applications (COTS or bespoke) that can profitably be supported. Scripting languages are generally designed to operate within one application domain, e.g., Bash, numerical analysis languages such as R and graphical plotting languages such as gnuplot.

While markup languages are very widely used they tend to be read and written by programs not people.

Having to read code containing non-alphabetic characters is always a shock the first time. Simply having to compare two sequences of symbols for equality is hard work. My first experience of having to do this in real time was checking train station names once I had traveled outside central Tokyo and the names were no longer also given in Romaji.

其中,ul分别是bootmap_size(bit map的size),start_pfn(开始的页框)
                                max_low_pfn(被内核直接映射的最后一个页框的页框号) ;

Developers based in China and India have many different cultural conventions compared to the West (and each other) and I suspect that these will effect the code they write (my favorite potential effect involves treating time vertically rather than horizontally). Many coding conventions used by a given programming language community exist because of the habits adopted by early users of that language, these being passed on to subsequent users. How many Chinese and Indian developers are being taught to use these conventions, are the influential teachers spreading different conventions? I don’t have a problem with different conventions being adopted other than that having different communities using different conventions increases the cost for one community to adopt another community’s source.

Programs written in a scripting language tend to be much shorter (often being contained within a single file) and make use of much more application knowledge than programs written in general purpose languages. Their data flow tends to be relatively simple (e.g., some values are read/calculated and passed to a function that has some external effect), while the relative complexity of the control flow seems to depend on the language (I only have a few data points for both assertions).

Because of their specialized nature most scripting languages will not have enough users to support any kind of third party support tool market, e.g., testing tools. Does this mean that programs written in a scripting language will contain proportionally more faults? Perhaps their small size means that only a small number of execution paths are possible and these are quickly exercised by everyday usage (I don’t know of any research on this topic).

Implementing the between operation

July 30th, 2009 5 comments

What code do developers write to check whether a value lies between two bounds (i.e., a between operation)?  I would write (where MIN and MAX might be symbolic names or numeric literals):

   if ( x >= MIN && x <= MAX )

that is I would check the lowest value first. Performing the test in this order just seems the natural thing to do, perhaps because I live in a culture that writes left to write and a written sequence of increasing numbers usually has the lowest number on the left.

I am currently measuring various forms of if-statement conditional expressions that occur in visible source as part of some research on if/switch usage by developers and the between operation falls within the set of expressions of interest. I was not expecting to see any usage of the form:

   if ( x <= MAX && x >= MIN )

that is with the maximum value appearing first. The first program measured threw up seven instances of this usage, all with the minimum value being negative and in five cases the maximum value being zero. Perhaps left to right ordering still applied, but to the absolute value of the bounds.

Measurements of the second and subsequent programs threw up instances that did not follow any of the patterns I had dreamt up. Of the 326 between operations appearing in the measured source 24 had what I consider to be the unnatural order. Presumably the developers using this form of between consider it to be natural, so what is their line of thinking? Are they thinking in terms of the semantics behind the numbers (in about a third of cases symbolic constants appear in the source rather than literals) and this semantics has an implied left to right order? Perhaps the authors come from a culture where the maximum value often appears on the left.

Suggestions welcome.