Concurrency and Message Passing in Erlang

November 5th, 2012  |  Published in concurrency, erlang, languages, message passing, performance  |  Bookmark on

In July 2011 I received an email asking if I would write an article about Erlang for the IEEE Computers in Science and Engineering (CiSE) magazine. The email said they had first invited Joe Armstrong but Joe had recommended me instead — how could I refuse a request like that? :)

It took awhile, but my resulting article “Concurrency and Message Passing in Erlang” is now published in the Nov/Dec 2012 issue of CiSE. Here’s the abstract:

Developers use the open source Erlang programming language in domains such as telecommunications, database systems, and the Web due to its superior support for concurrency and reliability. Erlang applications comprise numerous processes—lightweight user-space threads—that communicate via message passing. This article focuses on Erlang’s concurrency support and details an example 1D Poisson solver program.

Due to IEEE copyright rules I’m allowed to post only the final draft (PDF) sent to the magazine’s layout folks, but that’s OK since its text and figures are identical to the final published version. I haven’t yet received my hard copy of the magazine, but it looks like an interesting issue; it’s a special one covering concurrency in modern programming languages, and it also contains articles about Haskell and Clojure. The guest editors’ introduction explains the issue in more detail.

If you’re interested, you can purchase the full final article from the IEEE here. And now for some obligatory legalese: My article linked above is © 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author’s copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.

New Column: Roy

May 21st, 2012  |  Published in column, javascript, languages, web  |  Bookmark on

In the May/June 2012 issue of Internet Computing, Brian McKenna provides us with an excellent guest “Functional Web” column about Roy, a statically typed functional language that targets the JavaScript platform. Brian’s goals with Roy are to take advantage of static typing and functional programming to provide better safety and productivity for web programmers without forcing them to give up the ubiquitous JavaScript platform. Here’s the PDF of Brian’s clear and well-written article, loaded with informative code examples.

New Column: ClojureScript

November 5th, 2011  |  Published in clojure, clojurescript, column, functional programming, javascript, languages, web  |  Bookmark on

In the Nov/Dec 2011 issue of Internet Computing, “Functional Web” guest columnist Mark McGranaghan of Heroku gives us a really well-written article introducing the ClojureScript language and its Google Closure substrate. With a number of examples, he shows us how to use ClojureScript in dynamic client-side Web applications, and he also explains ClojureScript’s unique approach to JavaScript compilation.

[Update: I forgot to include a link to the actual article. Oops! Find it here. Thanks for letting me know, Stefan!]

As always, all feedback on this or any other “Functional Web” column is welcomed.

BTW if you enjoy the “Functional Web” column, be sure to attend the Functional Web track I’m running at QCon San Francisco coming up in mid-November. It’ll be fun and informative.

Joe Armstrong, Erlang, and RPC

May 27th, 2008  |  Published in distributed systems, erlang, languages, RPC  |  Bookmark on

Joe Armstrong explains the background of the distributed computing capabilities within Erlang.

I find postings like Joe’s highly valuable. Few among us are language designers, so rarely do those of us who aren’t get a first-hand account from someone who is as to why and how something within a given language’s design came to be. Joe describes the distribution primitives that Erlang provides as well as their composability; it might seem simple, but anyone who’s written non-trivial distributed computing infrastructure knows that choosing the right primitives and making the right design trade-offs is anything but simple. This explains why I continue to be so impressed with the design choices and trade-offs Joe and crew made for Erlang — I’ve simply never seen any distributed computing infrastructure so elegant and yet so practical and capable.

Thinking in Language, But Not Clearly

May 9th, 2008  |  Published in commentary, distributed systems, erlang, languages, reliability  |  Bookmark on

Ted Neward finally responds to my comments about his remarks concerning Erlang. I really don’t mean to pick on Ted — I like Ted! — but unfortunately, this time around his response misses the mark in more ways than one.

First, Ted says:

Erlang’s reliability model–that is, the spawn-a-thousand-processes model–is not unique to Erlang. In fact, it’s been the model for Unix programs and servers, most notably the Apache web server, for decades. When building a robust system under Unix, a master-slave model, in which a master process spawns (and monitors) n number of child processes to do the actual work, offers that same kind of reliability and robustness. If one of these processes fail (due to corrupted memory access, operating system fault, or what-have-you), the process can simply die and be replaced by a new child process.

There’s really no comparison between the UNIX process model (which BTW I hold in very high regard) and Erlang’s approach to achieving high reliability. They are simply not at all the same, and there’s no way you can claim that UNIX “offers that same kind of reliability and robustness” as Erlang can. If it could, wouldn’t virtually every UNIX process be consistently yielding reliability of five nines or better?

Obviously, achieving high reliability requires at least two computers. On those systems, what part of the UNIX process model allows a process on one system to seamlessly fork child processes on another and monitor them over there? Yes, there are ways to do it, but would anyone claim they are as reliable and robust as Erlang’s approach? I sure wouldn’t. Also, UNIX pipes provide IPC for processes on the same host, but what about communicating with processes on other hosts? Yes, there are many, many ways to achieve that as well — after all, I’ve spent most of my career working on distributed computing systems, so I’m well aware of the myriad choices here — but that’s actually a problem in this case: too many choices, too many trade-offs, and far too many ways to get it wrong. Erlang can achieve high reliability in part because it solves these issues, and a whole bunch of other related issues such as live code upgrade/downgrade, extremely well.

Ted continues:

There is no reason a VM (JVM, CLR, Parrot, etc) could not do this. In fact, here’s the kicker: it would be easier for a VM environment to do this, because VM’s, by their nature, seek to abstract away the details of the underlying platform that muddy up the picture.

In your original posting, Ted, you criticized Erlang for having its own VM, yet here you say that a VM approach can yield the best solution for this problem. Aren’t you contradicting yourself?

It would be relatively simple to take an Actors-based Java application, such as that currently being built in Scala, and move it away from a threads-based model and over to a process-based model (with the JVM constuction[sic]/teardown being handled entirely by underlying infrastructure) with little to no impact on the programming model.

Would it really be “relatively simple?” Even if what you describe really were relatively simple, which I strongly doubt, there’s still no guarantee that the result would help applications get anywhere near the levels of reliability they can achieve using Erlang.

As to Steve’s comment that the Erlang interpreter isn’t monitorable, I never said that–I said that Erlang was not monitorable using current IT operations monitoring tools. The JVM and CLR both have gone to great lengths to build infrastructure hooks that make it easy to keep an eye not only on what’s going on at the process level (“Is it up? Is it down?”) but also what’s going on inside the system (“How many requests have we processed in the last hour? How many of those were successful? How many database connections have been created?” and so on). Nothing says that Erlang–or any other system–can’t do that, but it requires the Erlang developer build that infrastructure him-or-herself, which usually means it’s either not going to get done, making life harder for the IT support staff, or else it gets done to a minimalist level, making life harder for the IT support staff.

I know what you meant in your original posting, Ted, and my objection still stands. Are you saying here that all Java and .NET applications are by default network-monitoring-friendly, whereas Erlang applications are not? I seem to recall quite a bit of effort spent by various teams at my previous employer to make sure our distributed computing products, including the Java-based products and .NET-based products, played reasonably well with network monitoring systems, and I sure don’t recall any of it being automatic. Yes, it’s nice that the Java and CLR guys have made their infrastructure monitorable, but that doesn’t relieve developers of the need to put actual effort into tying their applications into the monitoring system in a way that provides useful information that makes sense. There is no magic here, and in my experience, even with all this support, it still doesn’t guarantee that monitoring support will be done to the degree that the IT support staff would like to see.

And do you honestly believe Erlang — conceived, designed, implemented, and maintained by a large well-established telecommunications company for use in highly-reliable telecommunications systems — would offer nothing in the way of tying into network monitoring systems? I guess SNMP, for example, doesn’t count anymore?

(Coincidentally, I recently had to tie some of the Erlang stuff I’m currently working on into a monitoring system which isn’t written in Erlang, and it took me maybe a quarter of a workday to integrate them. I’m absolutely certain it would have taken longer in Java.)

But here’s the part of Ted’s response that I really don’t understand:

So given that an execution engine could easily adopt the model that gives Erlang its reliability, and that using Erlang means a lot more work to get the monitorability and manageability (which is a necessary side-effect requirement of accepting that failure happens), hopefully my reasons for saying that Erlang (or Ruby’s or any other native-implemented language) is a non-starter for me becomes more clear.

Ted, first you state that an execution engine could (emphasis mine) “easily adopt the model that gives Erlang its reliability,” and then you say that it’s “a lot more work” for anyone to write an Erlang application that can be monitored and managed? Aren’t you getting those backwards? It should be obvious that in reality, writing a monitorable Erlang app is not hard at all, whereas building Erlang-level reliability into another VM would be a considerably complicated and time-consuming undertaking.