Summer reading on actors

For a popular topic, I do not see enough design discussions around Actors online. It could be difficult to learn about idioms or pitfalls without going deep into OTP or Akka. Off the top of my head I can think of only two interesting blogs:

• James Iry wrote a fascinating series on why Actors are not a silver bullet for all things concurrent. He is such a polished author you should read his posts even if you don't care much about Scala/actors.

• Somebody started recently a very informative blog with detailed examples of actor-based FP-style designs.

Object block initializor

Object block initializor in Java is a code block in parenthesisexecuted before the class constructor. I always thought it was a bad idea because by default I expect all initialization code in a constructor. In addition, I have never seen such initializors used anywhere except for Java textbooks and interview questions.

Yesterday I for the first time read about a potentially useful way to utilize them. The idea is to save some typing (compare creation of b1 and b2):

Thunk

I first learned about this approach to lazy initialization a few months ago but every time I look at its Java implementation I think it's a really cute piece of code. I wonder why my book on Singletons did not mentions it :)

Sizing up Java employers

While trying to understand what kind of company I would like to work for next I made another observation on employers in the Java land. At first glance they fall into three categories:

• Typical Java shops doing something of little interest from the engineering point of view. Their job descriptions usually mention Spring and Hibernate. Frequently they also ask for either JEE or presentation tier technologies a-la JSP/Struts (IMO the latter is a particularly strong indicator you do not want to work for them).
• Companies working on something more challenging or in more exciting domains. For me a good indicator is that they ask for more advanced/less known technologies such as Lucene, Hadoop or one of the numerous DHT implementations.
• One-of-a-kind companies, GOOG-style. They do not list any particular technologies except for Java itself. They are explicitly after what they refer to as "bright people".

Meaningful approach to interviewing?

My current company is still looking for a Sr. Java developer in SF and I am usually one of the 1st round interviewers. Naturally, it makes me ponder on the optimal approach to interviewing. Recently I started noticing that on more and more topics my real answer is "it depends". It also frequently requires we agree on some conceptual model. I do not believe in the universal best answer to an important question but I also recognize that in real life any progress is possible only when one actually chooses and pursues one of the possible answers.

Interviewing is not any different. In my life I have witnessed at least five distinctly different interview types:

• No real questions - you chat with a few members of the team but they do not test you. You tell them about your background, ask about their system and answer a couple trivial technical questions. Strangely enough, I worked almost five years for two companies that hired me in this style. Although I heard some people think it's a red flag (as in "Do you really think they will have sufficiently bright people with such poor screening?") one of those two was the best company in my eleven years. And yes, it happens in the US too.

• Outsourcing-style - an endless stream of extremely low-level technical questions on particular technologies and APIs. RDBMS isolation levels, the servlet lifecycle, the methods on EJB home/remote interfaces, JSP scopes. A design pattern for them is always one from the GOF book or Sun J2EE patterns guidelines. Characteristically, they do not care about your design skills or code quality and really like J2EE-style.

• CS undergraduate-style - in my opinion a questions such as "implement a RW-lock on the whiteboard" is a good example. Surely enough, real-life locks have nothing to do with whatever you will come up with in 15 minutes and, unless they prepared specifically, quite a few people will probably not be able to remember enough textbook material.

• Common sense-style - reverse a list. Suggest a design for logging system. Implement a Map with additional non-standard requirements. You can answer them on the basis of real-life experience or with some thinking of the kind you do day-by-day at work.

• GOOG-style (actually, I read it was MSFT who originated it) - CS undergraduate on steroids with a puzzle or two to load. Personally, I was not happy during some of those interviews, especially the ones I knew I was blowing badly :) Incidentally, I also learned a lot from them. But when I have only an hour with a candidate I am not quite sure which approach to follow.

From what I see, a typical Java-centered company is either a J2EE enterprise or a place where they care about util.concurrent. Amusingly, this seems to be a very clear dichotomy. In both cases, there is a pile of [de facto] standard APIs and frameworks which take considerable time to master. And people who gravitate to one of the two types tend to be rather apprehensive if not ignorant of the other. I am also inclined to think that very little of even basic algoritms&data structures material is used in those companies. At least not deeper than TreeMap v HashMap and such. So asking more theoretical questions seems almost unfair (and not justified by actual day-by-day development needs).

As an example, today I interviewed another "Sr. Java" engineer. He did not know exactly what the volatile keyword meant (wtf? after all it's a keyword and not some obscure optional library). He was immediately confused with "try { foo(); return 1; } catch (Exception e) { return 2; } finally { return 3; }". And so on. He stated Hibernate experience in his resume but he actually meant "experience in calling Hibernate via JPA". Obviously he did not know about caching capabilities of Hibernate or mapping of OO models on relational schemas although it takes one book and a weekend to learn about. Frankly, I cannot imagine how a senior-level engineer could be so ignorant. After all, you learn by osmosis at work and glean questions from interviews throughout your career.

But what's the point of discussing, say, software architecture with people who fail simple questions relevant to daily coding? In a language universally regarded as outdated and extremely simple? Someone knowledgeable of actual CS must be pretty comfortable with basic hashCode/equals/HashMap stuff. Could I be gratuitously harsh on candidates because of some misplaced self-righteousness? Or I am right in that people who are too lazy to read half a dozen books before an interview do not deserve much? Or is my current company so unappealing that only losers apply?

Seniors among Java engineers

If you were to trust what you read on the Net you would think Java is a brain-dead language and people who develop in Java are the alternatively gifted among software engineers. While the former is a multidimensional question the latter could make you nervous if you've been in the Java land for many years. Allegedly, in some circles a decade of predominantly Java experience raises a red flag.

I am inclined to think that Java is mostly infamous for its enterprise branch. Surely once fashionable J2EE technologies are good for outsourcing but the damage they inflict on developers is very real. But if you ask me, I'd rather do EJB2 than any kind of web UI from JSP to ajax. Luckily I have not had to deal with either for a long time.

Occasionally I participate in interviewing potential future coworkers. And some of them position themselves as Sr Java engineers and even have CS major backgrounds. You would think that in the Bay Area developers are likely to be a uniformly enlighten group. After all, this is arguably the most expensive place to hire and an international magnet for software engineers.

Not really if my experience is representative. I have interviewed and even worked here with people who demonstrated almost appalling lack of professional skills (e.g. decent OO design with proper decoupling and meaningful responsibility assignment) or relatively basic knowledge (the role of hashCode/equals in the HashMap context, anyone? optimistic/pessimistic locking strategies? ACID? mapping of class hierarchies on relational DB tables?). On a few occasions after a decade or two in the industry.

Or is it just me? Probably I am supposed to ask candidates to implement a RW lock (unless your name is Doug or Brian I'd rather know you are intimately familiar with the util.concurrent package) or recursive tree scanning? But those look like more advanced concepts to me than the difference between volatile and synchronized in protecting a long variable. And it's not like in their defense they could show years of non-OO (although I am pretty sure FP folks are into good design, only by different means) or non-Java/C++ experience (then again, what makes him a Sr Java engineer?).

Could it be the case that Java is merely so dominant that it covers wildly different domains (e.g. util.concurrent/NIO v J2EE; telecoms or financial middleware v a web UI for DB access) and we do not have specific terms for people with the corresponding expertise?

Best sticky note presentations on concurrency ever

I stumbled upon a few very impressive, useful and uniquely designed presentations . They discuss a few classical but very realistic concurrency problems using a distinct visual and didactic approach. Frankly, I have never seen anything like that, the author seems to be in a league of his own.

The only inconvenience is that you need a connection all the time because the system hosting those presentations does not cache all the images.

How to leak Linux pipes from Java code

Fixing a bug in legacy code I found a moderately counter-intuitive rule for dealing with Process instances returned by Runtime when one executes a process. It turns out that the three standard streams associated with each instance must be closed regarless of whether you use them anywhere in your code.

By default I expect that unless I explicitly open something there is no need to close it manually. Moreover, I double-checked javadocs and Java Programming Language and I have not found any related warning. On the other hand as it happens on the boundary between java world and OS it is probably natural to expect very strict requirements for disposing of unused resources. At least it was not me who wrote that code in the first place :)

An easy way to check if pipes are leaked is to run something like "/usr/sbin/lsof | grep pipe | grep java" and see if the number is growing. In my experience if you get a "too many open files" error it's likely to be either about leaking pipes or sockets (if you can see an unreasonable number of sockets in CLOSE_WAIT state in netstat output).

They knew it but they still ended up with Java as we know it

Ten years ago I did not know who Guy Steele was or that I would spend years programming in Java. Seven years ago I thought that a language without operator overloading and templates was an ugly toy. A few years later I got so used to it I mostly stopped worrying.

It turns out Java authors were not morons. They might have thought that the users of their language were. Or they just could not imagine that a language for programming refrigerators (or was it set top boxes?) would be of any wider use. What is painful to learn in hindsight is that they knew about all the good suff , liked it a lot themselves but somehow chose to ignore it.

Big4 on YouTube

Recently I noticed that the Big 4 (i.e.MIT/Stanford/Berkeley/CMU) shared a number of their introductory courses online. At first glance, only Stanford and Berkeley actually have a few CS-related ones. MIT shared mostly general engineering/math courses while CMU, the home of robotics and software engineering, has virtually nothing online.

I am watching two courses currently to get some idea of Lisp/Scheme and how the best and the brightest are inculcated true meaning of CS in general :)

Stanford

• Programming paradigms - a very nice review of a few languages (from Assembly to Python) including four or five lectures on Scheme. The lecturer is very energetic and gives an impression of someone who has real life experience.

Berkeley

• CS61A Structure and interpretation of computer science - more of a CS course using a Lisp dialect than a language course which arguably makes it even better. The lecturer here is less impressive and at times seems to be too old (incidentally, the equipment is also less shiny than at Stanford .. is there some kind of correlation?). There's also CS61B but it seems to be based on Java (?!) so it is less likely to be of significant interest.

MIT

• MIT 6.001 Structure and interpretation of computer programs- vintage '86 edition, narrated by Messrs. Abelson and Sussman themselves.

In addition, there are a couple more courses on subjects such as robotics and machine learning but those have less immediate applicability. So I encourage you to browse their offerings.

Book marketing for real programmers

ForkJoinWorkerThread.java :

"... If you are unfamiliar with them, you probably want to read Herlihy and Shavit's book "The Art of Multiprocessor programming" ..."

The book seems to be JCiP on steroids (would you expect less from something Doug Lea himself refers to? :) ) with 100+ pages on theory (pretty standard topics with nice illustrations, Java-friendly examples and quite detailed explanations) and 500 pages of everything you always wanted to ask Doug about (personally, I would not expect to understand most of the answers anyway, at least before reading this book).

It took me five cover-to-cover readings of JCiP (guess who is the slow one in my family? :) ) to get sufficiently comfortable with the subject. And I still occasionally re-read parts of it. AoMP addresses much harder questions although is probably less practical unless you are writing your own j.u.c or want to understand how the real one works.

Small language changes for JDK7

I am a thoroughly conservative guy and quite naturally tend to be a late adopter even if I am aware of a particular new technology in general. Watching a panel on future of Java on infoq.com a couple of years ago I was quite surprised by people of Joshua Bloch caliber discussing Java as a probably mature/declining language.

Back then I expected that somehow that language changes of Java5-magnitude would be added with each new release. I believe that only in Java5 the language was getting some of the C++ power it was originally deprived of (e.g. STL and all the features enabling it). So it felt as Sun finally decided to get serious about the language and stop dumbing it down to almost VB level.

Surely enough the titans were right and saw it coming even back then. In contrast to the JVM (as in garbage collectors or contested monitor performance) Java does not seem to have meaningful progress anymore. Syntactic sugar just is not worth it in my opinion. And Doug Lea seems to be the only one pushing Java's limits.

Things like catch blocks for multiple exceptions do not bring much to the table, not to mention all the legacy code which is not likely to be migrated. And to have mixed styles in the same code base is even worse than to have gratuitious blocks in the first place. As a creature of habit, I do not even notice such things anymore, I code them on auto-pilot.

Last year I was reading the Erlang book and got so confused with FP idioms that I had to digress and read the Scala book to better grasp what all the FP hype was about. It did not convert me from OOP but definitely made me appreciate FP (and incidentally reminded me about STL which enabled all the FP-style fun with lists fifteen years ago).

And somewhere down that road I found myself thinking that I do not want Java to be changed dramatically anymore. An attempt to make Java more sophisticated would result is a limited version of, say, Scala. It would be a new language and all the existing code would immediately become non-idiomatic. Or in the worst case there would be just a few special cases hard-coded into the language instead of meta-protocol-like facilities.

So, if even I have this funny feeling that any potential Java upgrades (years ahead, and some people have not migrated even to 1.6) are not as appealing as a modern language such as Scala probably the tide is actually turning.

Programmer Competency Matrix

It is not he first such matrix but it made me think a little. In a week I will be celebrating my first ten years in professional software development. And looking back I can only laugh at myself back then. It's been a long way from almost "Unable to find the average of numbers in an array" but log(n) (Level 3)-like requirements show that the next decade will probably make me feel something similar :)

Programming in Scala on Actors

I am through my first reading of the book and somehow it seems to be less helpful than I hoped it would be. I do not think it is bad or merely repackaged online documentation but I guess I expected more from a book written by the language author. Sublime wisdom or something :)

I believe most people are interested in Scala because it is an OOP-friendly tool for learning practical FP and Actors. So I was particularly irritated by chapters on GUI (who cares?) or minute details on integration with Java (better to be online instead of wasting precious book space). On the positive side, my feeling is that FP is covered in the book adequately.

What truly disappointed me was the chapter on Actors. To begin with, why only 1 chapter on this exciting topic? It is not like best Actor practices are better known than FP among us mere mortal with mostly C++/java background. And in my opinion that event simulator example is actually a good illustration of what not to do.

What I wanted to see was a clear comparison with traditional concurrent designs. So some universally-known concurrent system (e.g. a network /web server) would not require any explanation what it is and would immediately conjure up many examples from java world. Some code snippets would be probably even useful in real life. Not only modelling circuitry won't, it actually complicates the discussion with essentially unrelated clutter.

In addition, it would be really useful to learn how all this Actor machinery actually works. Is it some native magic or just a Scala library? How does it compare with j.u.c-based abstractions, at least performance-wide? Not a single word.

As a matter of fact, there is a much more elucidating paper named Actors that Unify Threads and Events. It really helps to read it before you delve into the dark internals of Actor.scala. It turns out that some interesting (and somewhat dirty? or truly ingenious? exceptions for control flow ..) design decisions were made to make it work.

As for the Actor-related code itself, I found it quite messy. Makes me wonder if the root cause was extreme performance fine-tuning or certain sloppiness. There is even a recent post where an independent Scala enthusiast comes up with a more orderly design of Actor.scala (and provides a few more hints on the official design). Hopefully Martin&Co will listen to him.

Is Java relevant?

My previous post made me think about my attitude towards Java. Even if it happens to be behind its pinnacle, is Java any good beyond paying my bills for years? If we know what Java gave this world probably we will be better equipped to decide when to move to a new language and how to judge it.

History teaches us that non-technical aspects matter more than what is habitually referred to as technical excellence. Which is actually difficult to define. I have a growing suspicion that what matters a lot is something I would call, for a lack of standard term, "age and experience demographics". The idea is that certain technologies are perceived to be cool by people entering the field. Those technologies in a sense create an imprint on that particular generation.

As an example, in the early nineties Assembly was for real men and C++ for real programmers. At least how I felt it back then under certain circumstances (no influence from CS-savvy people, and extremely limited literature in the absence of the Internet, most people using and targeting MSFT platform). I know that years before I discovered computers people had been writing in HEX code and considered Assembly to be unmanly. It very well may be that nowadays something like scripting/dynamic languages are all the rage among the young.

There must be also a heavy influence of experience resulting in some kind of "shifting interest curve". You need to be through a complete life cycle of a major language such as Java to be able to see that not everyting is new under the sun. As an example of a self-made developer, I have progressed through Pascal, C++, OOP, OOA&D, RUP, UML, Java, algoritms and data structures 101, development methodologies, software architecture, really understanding OOA&D, really understanding Java concurency, TDD (disclaimer: for simplicity sake the sequence was artificially serialized and stripped of many things).

Right now I value good analysis and design (assuming OOA&D; I am not aware of FP/dynamic language alternatives to it; and yes, I appreciate UML) and best software engineering practices more than a particular language. I like reading about algorithms much more than I did ten years ago. I am dabbling with FP in its safely diluted incarnation (Scala) and planning to look again at Erlang later next year. Who knows, probably in my next ten years I will be able to get interested and even like highbrow stuff such as LISP. The point is that in addition to normal technological progress each individual has another learning curve which includes things not affected directly by his current job.

And last but not least, not everyone majored in CS. As a matter of fact, I believe I have worked with more people from Engineering/Physics backgrounds than properly educated CS graduates. Naturally, the former were not indoctrinated in seemingly non-practical subjects such as LISP, FP or even the details of compiler design. Some of those are probably later picked in spare time but I would still expect a gap between originally CS and non-CS folks.

So, what do I like about Java? I happen to maintain an Apache module written in C and every time I fix a bug there I appreciate our warm and fuzzy Java world more. This juxtaposition elucidates good things about Java although by no means it is even remotely scientific or exhaustive. Disclamer: borders between Java the language, the JVM and Java ecosystem at large are blurred to reflect real life.

• Java has a standard API (or a de facto standard API) for nearly everything. And innumerate open-source implementations of those.
  
• Java has multiple open-source components available for anything from reliable messaging and IoC to web UI and Map/Reduce on serious scale.
• We have a set of widespread mature technologies covering most important mundane areas (e.g. Maven/Spring/JUnit)
• Java has a memory model and an amazing util.concurrent library. It was Doug Lea and not James Gosling who was my youth hero :) And Brian Goetz wrote really nice javadocs :)
• Java has a decent Collections libraryJava dominates the server side. Jobs are abundant in interesting domains from Finance to Telecommunications
• Java promotes OOP and interface-based design. Not really design by contract though :(
• Because Java is a dumbed-down language, it is easy to read (well, multi-screeen methods are still found out there but I guess you catch my drift). Though I have always missed overloaded operators and proper generics (enabling the STL library in C++).
• Nowadays there are enough high-quality Java books
• Without IntelliJ IDEA I would go out, shoot myself in the foot and die :)
• Java does not look weird (presumably in comparison with the C branch of evolution)

Most of us would be able to continue this list for a long time. When I look at it the point seems to be indeed that it is not about Java the language. Libraries and the JVM sneak into the picture all the time. As a creature of habit I like Java because I am used to it but if a JVM language more sophisticated than Java comes along I would be all for it.

Harking back to Scala, the language looks smart to me (yes, I am enamored with C++ like complexity and things like covariant/contravariant type annotations attract me rather than scare away). I detest languages that restrict me (Java more than C++, Erlang more than Scala). I cannot imagine living with a language where I would not be able to do OOP even if I like the idea of trying out at least elements of FP. And Martin reminds meBjarne more than others do :)