Archive for May, 2014

Source code will soon need to be radiation hardened

May 29th, 2014 2 comments

I think I have discovered a new kind of program testing that may soon need to be performed by anybody wanting to create ultra-reliable software.

A previous post discussed the compiler related work being done to reduce the probability that a random bit-flip in the memory used by an executing program will result in a change in behavior. At the moment 4G of ram is expected to experience 1 bit-flip every 33 hours due to cosmic rays and the rate of occurrence is likely to increase.

Random corrupts on communications links are protected by various kinds of CRC checks. But these checks don’t catch every corruption, some get through.

Research by Artem Dinaburg looked for, and found, occurrences of bit-flips in domain names appearing within HTTP requests, e.g., a page from the domain being requested rather than from A subsequent analysis of DNS queries to VERISIGN’S name servers found “… that bit-level errors in the network are relatively rare and occur at an expected rate.” (the 2.10^{-9} bit error rate was thought to occur inside routers and switches).

Javascript is the web scripting language supported by all the major web browsers and the source code of JavaScript programs is transmitted, along with the HTML, for requested web pages. The amount of JavaScript source can dwarf the amount of HTML in a web page; measurements from four years ago show users of Facebook, Google maps and gmail receiving 2M bytes of Javascript source when visiting those sites.

If all the checksums involved in TCP/IP transmission are enabled the theoretical error rate is 1 in 10^17 bits. Which for 1 billion users visiting Facebook on average once per day and downloading 2M of Javascript per visit is an expected bit flip rate of once every 5 days somewhere in the world; not really something to worry about.

There is plenty of evidence that the actual error rate is much higher (because, for instance, some checksums are not always enabled; see papers linked to above). How much worse does the error rate have to get before developers need to start checking that a single bit-flip to the source of their Javascript program does not result in something nasty happening?

What we really need is a way of automatically radiation hardening source code.

Oh, I did not know that [about R]

May 20th, 2014 No comments

I recently saw a post about something called ValidR and as somebody with a long standing professional interest in language validation immediately read the article and referenced links. I was disappointed to find that what was being validated was the installation, not the behavior of the implementation. In the context of what I understand ValidR’s target market to be, drug testing, obtaining reproducible results is very important and so it is necessary to know exact what software has been installed (e.g., packages and their versions).

Implementation validation involves checking that the implementation of a language adheres to the requirements specified in the appropriate language standard. While International standards exist for many of the widely used languages, some have standard’s developed through other means and some have no recognized specification at all (e.g., PHP, Perl and R).

Not having a recognized specification is a problem for PHP because there are multiple implementations in common use. Perl and R both have a dominant implementation, which means the definition of the language is accepted as being whatever that implementation does.

Now, anybody who claims that having an open source implementation is as good as having a specification written in English (i.e., people can read the code to discover the behavior) clearly have not done much, if any, reading of language implementations. Over the years I have worked with the source of a fare few language implementations and my general experience is that the fastest and most reliable way of finding out what an implementation does is to write test case, only reading the source when test cases cannot be found that answer the questions.

Does it matter that there is no complete English specification of R (the current specification is very much a work in progress, with lots of progress remaining)?

Who reads computer language specifications (apart from language wonks like me)? Creators of implementations is the most obvious answer. But an R implementation already exists, why should the R team spend time making it easier to create alternative implementations? Actually I see the main customers of an R language specification being the R-core team.

An example of the benefits to the owner of source code in having a specification is provided by the EU/Microsoft competition court case. I was an adviser to the Monitoring Trustee appointed by the Commission to oversee the documentation of the specification of these protocols (no previous documentation existed). A frequently heard comment from the senior Microsoft developers we dealt with, on reading their own new specifications, was “Oh, I did not know that”.

A written specification is much more compact than source code or test cases and is (or should be) organized in a way that helps readers understand what is being said (this is often a stated aim for source code but is rare achieved). There are probably lots of behaviors that the R team are unaware of which, if they get to find out about them, might be interested in ‘fixing’ or at least discussing whether it is a desirable behavior. Or perhaps the R team’s strategy is to make life difficult for competing implementations.

APIs can, for the time being, be copyrighted

May 11th, 2014 1 comment

There was an interesting turn of events in the Oracle vs. Google Java API lawsuit last friday. The original trial judge had ruled that an API are not copyrightable; last week the US federal Court of appeals reversed this decision, APIs are copyrightable. This legal battle is not over and the ruling can flip and flop its way up to the US supreme court, and not being a lawyer I’m happy to leave the legal discussion to others. Let’s assume that Oracle eventually win their Java API copyright claim, what does that mean for computer language usage and software developers?

If Oracle’s API copyright claim is upheld then they are potentially in line for a huge payout (Google might get to wiggle out of paying much via a fair use justification). I’m sure that some people will claim that this ‘win’ will kill off Java, even if this is true (I don’t think it is), what do the suits care? Give me a billion dollars and I will happily support the removal of any computer language from planet Earth.

In the early days of Android Google needed Java compatibility more than Java needed anything to do with Android. Now Android has such a commanding market share Google does not need to worry so much about Java compatibility. If Oracle had any interest in the future of Java they would be worried that this court case could result in Google switching the Android ecosystem to using a slightly incompatible Java-like language. In practice this court case is the only real opportunity for Oracle to make serious money from their Java intellectual property and they are not that excited about a steady stream of peanuts from future goings on.

What does Oracle winning the API copyright claim mean for developers?

If Google do launch a Java-like language then Java’s “write once run anywhere” mantra will be less true than it currently is (by avoiding a few traps and not straying too far from the well trodden path Java developers can create programs that are remarkable portable). In its market niche there is no other language that comes close to providing the kind of portability that Java offers, so existing users will be annoyed at having to worry about one more portability issue but are unlikely to jump ship.

The much more interesting question is the impact an Oracle win has on other companies producing products that include an API; they now have something to wave at competitors who have API-alike (I just made that word up) products. Any developer using an API that has its very own copyright discussion thread is likely to become a bit twitchy. The general result will be a cloud of uncertainty over some existing APIs from some providers.

Anybody introducing a new API will have to answer the ‘copyright’ question: “Do you claim copyright on your API?” In practice a very very small percentage of APIs ever get copied/cloned, because most fail or the competition comes up with what they think is a better API.

Would I care if a company claims copyright on its API and says it will sue anybody who copies/clones it? Obviously I have to use that API if it is the only way to get a job done, but what if I had a choice between it and a non-copyrighted API? I don’t think the question of copyright would be an issue for me, but I would be concerned if any company was being overly legalistic; do I really want to deal with a company more interested in legal matters than supporting developers? I think not.