Haskell Fibonacci Revisited

Recently, there was an interesting post about Haskell performance and Haskell parallelization showing Haskell could outperform C on a simple Fibonacci example.

A friend of mine, Peter (that I seem to manage to constantly piss off) thought about it on another level, saying you could achieve a _MILLION_ times better using a direct formula in C or Java, the Binet formula.

I decided to try as the improvement scale seemed a bit surprising. I first compared a Java recursive fibonacci with a Haskell one. Here are the results for Haskell GHC 6.6.1 vs Java 1.6.0 on Linux for fib(44):


Then I decided to check out the time for fib(44) or any fib at all, I was unable to measure precisely enough since it always came out as 0ms, in Haskell, or in Java. Looping out 10 million times, Java gave out 7.3s and Haskell something similar (but my method to loop 10 million times in Haskell is probably very bad).


The original post actually points to a link that describes various algorithms for Fibonacci. They basically say that for large n, the rounding is not precise enough, they also propose algorithms in log(n). I tried and was really impressed by the performance of those algorithms. Again I could not measure the difference for a single calculation between it and the binet formula as elapsed time is always 0. The binet formula becomes inexact already at n=71 in Java with doubles.


Of course the original post is still quite interesting, it shows how easy it can be to parallelize calculations in Haskell. But the example is silly as another algorithm can lead to 10 millions times the performance. Still Haskell performs well with the shit or good algorithm when compared to Java.

Ubuntu 7.10 vs Fedora Core 8 - Gutsy vs Werewolf

I was pretty happy with Ubuntu 7.10, but when Fedora 8 came out I decided to give it a try. Last time I tried it it was Core 2 or something like that, and it was NOT good.

At first Fedora 8 looks quite good, has a good Live CD install, reminiscent of Ubuntu. The positive side is that it is based on the latest Kernel. It manages my Thinkpad T42 very well (suspend, hibernate work). But after a few days, one notice Fedora is not as stable as Ubuntu, for example:

  • I have had weird behavior with windows not being updated properly
  • I experienced big problems when playing with LVM,
  • It is also a general impression when interacting with the system.

One can wonder why Fedora 8 does not install OpenOffice by default.Ubuntu is IMHO still the king of distros.

Apache DbUtils Completely Useless

I am disappointed about the Jarkarta Commons DbUtils project. I give a link to it, because it’s a bad project (even if written in clean code). It is very simple, but it really does not do much for you.

I was looking for a very simple abstraction of JDBC. I thought bringing Spring in my project would be overkill. After trying DbUtils, I think again. It does not help. It does not handle frequent cases well, and it does not save many lines of code.

I am a bit angry about it as I noticed that by using it, my test program that was taking 2s with straight JDBC before is now using 1 minute!

The reason behind this huge performance penalty is that there is no way to just reuse a PreparedStatement with the existing classes. For each query with a same sql, it will create a new PreparedStatement object, even if you reuse the connection. I am surprised since this is probably why PreparedStatement is used in the first place. How can such a project be part of Jakarta repository?

Now I just wish Spring was more Guice like, maybe I should write a Spring JDBC like layer for Guice.

I fell in the trap of Boolean.getBoolean()

I was struggling to find a bug in a very simple application, it ended up being something as simple as using the damned Boolean.getBoolean("true") call instead of Boolean.valueOf("true").booleanValue() call.

The Boolean.getBoolean method is something you almost never need to use, as it checks if a particular system property is true or false. There is a similar method for Integer.getInteger, and a quick google search shows I am not the only one to think those method should never have been part of the basic API for Boolean/Integer. It is too easy to confuse with parseBoolean/parseInt, especially as parseBoolean does not exist in JDKs prior to JDK 1.5 (parseInt is older).

I can not imagine the improductivity this method has produced given its part of one of the most used class in the world.

Fast Web Development With Scala

I am currently experimenting with Scala. It seems quite convenient for web applications. Using Tomcat, it is possible to have a very productive developer environment.
Here is a sample Embedded Tomcat you can start in a Scala project:
import java.io._;
import org.apache.catalina._;
import org.apache.catalina.startup._;

object TomcatScalaServer {
  
  val CATALINAHOME : File = new File("../newsbeef.com");
  val WEBAPPS : File = new File(CATALINAHOME,"webapps");
  val ROOT : File = new File(CATALINAHOME,"web");
  val HOSTNAME : String = "localhost";
  val PORT : int = 8080;
  
  def await() {
     while( true ) {
          try {
            System.out.println("sleeping 100s");
              Thread.sleep( 100000 );
          } catch {
            case ie : InterruptedException =>;
          }
      }
  }
  
  def start() {
    val server = new Embedded();
    server.setCatalinaHome(CATALINAHOME.getAbsolutePath());

    val engine = server.createEngine();
    engine.setDefaultHost(HOSTNAME);

    val host = server.createHost(HOSTNAME, WEBAPPS.getAbsolutePath());
    engine.addChild(host);

    val context = server.createContext("", ROOT.getAbsolutePath());
     context.setParentClassLoader(Thread.currentThread().getContextClassLoader());
     context.setReloadable(true);
    host.addChild(context);

    server.addEngine(engine);

    val http = server.createConnector(HOSTNAME, PORT, false);
    server.addConnector(http);

    server.start();
  }
  
  def main(args: Array[String]) {
    start();
    await();
  }

}

Here is a sample Scala Servlet outputing html directly. This is a simple example, but it shows something important. With Scala, the view layer can just be regular scala classes. There is no need for JSP or other templating languages as Scala already embbeds XML very nicely. By using the reloadable feature of Tomcat (there are also other pure Scala ways) and Eclipse autocompile, changes are instantanously taken in account.
import javax.servlet.http._;

class ScalaServlet extends HttpServlet {

  override def init() {
  }
  
  override def doGet(request : HttpServletRequest , response : HttpServletResponse) = {
    service(request, response)
  }
  
  override def service(req: HttpServletRequest,resp: HttpServletResponse) { 
    val pw = resp.getWriter();
    var output = <html>
    <head><title>Scala Servlet Test</title></head>
    <body>
      <h1>Hello World!</h1>
    </body>
    </html>
    pw.println(output);
    pw.flush();
  }
}

Now I am eagerly waiting for improvements in the Eclipse Scala plugin (Organise imports, class navigation).

2 Months of Ubuntu on Mac Mini

I am finally happy with my OS. I had previously [some complaints]({{ relref . “1-year-of-mac-mini–the-deception-point.md” }}) about MacOs X and the Mac Mini. It is now over, with Ubuntu, I am very happy of my quiet system.

I use Quod Libet for Audio, it has similar interface as iTunes, with more features (ability to play most audio formats). I chose Quod Libet instead of the standard Rhythmbox because of its practical mp3 tags handling. This also means that unlike iTunes, when I reimport my full library with another player, or on another computer, I have it all organized the right way, because the right meta data is in the audio files and not in a xml file that sometimes gets corrupted.

I can use Open Office (not yet available in non alpha version for Mac Os X).

I can use Picasa or other more standard alternatives instead of iPhoto.

I can use free guitar tuners, plenty of esoteric software.

Remote control, fancy bluetooth apple keyboard, cd burning, dvd player, printer work flawlessly. And it’s all free software (except Picasa which is only gratis).

I am happy with my Ubuntu system :).

Spring Web Services, Finally!

Spring Web Services seems to be the technology I have been looking for recently. I am not a Spring bigot (too XML oriented), but here the Spring folks have something right.

I used to work with Web Services the simple way: create a java class (or EJB), expose it as Web Service through Axis or RAD, generating the WSDL in the process. And then a client would just be the reverse, take the WSDL, use a tool (Axis or RAD) that creates client Java classes from it automatically. Simple, easy.

But this process starts to fail if you have:

  • several very similar WSDL: you want reuse instead of copy.
  • other means of communicating XML represented by the XML schema embedded in the WSDL, for example via direct MQ use.

In those cases, the contract first approach is particularly interesting. However most tools, if they allow contract first approach, they don’t give you enough access on the message itself, and you can do 1), but not 2). I always found a bit silly that Axis or RAD had to have the logic to marshall/unmarshall java objects, but they did not give any explicit API access to do it, or to replace it with a standard way (JAXB 2 for example).

I found 2 techs that can help:

  • SDOs (Service Data Objects): from my short experience, I find it a bit too verbose, and not yet fully mature, as you depend on libraries external to SDO ones for it to work in the case of web services. It can work, and if you use IBM products, it could be a good way to write Web Services Providers/Clients.
  • Spring Web Services: I have not tried it yet, but it seems to solve exactly the kind of problems I described earlier. And you can plug-in any marshalling/unmarshalling framework you want :).

There are so many libraries to do web services, and different approaches, that an initiative like Spring Web Services is more than welcome!

Original Pattern: ServletRequest in ThreadLocal

After seeing Scala had elements of Erlang through Actors, I decided to take a closer look at the language. There is an interesting new web framework in Scala, called Lift. One drawback of Lift is that it seems to be very cutting edge and not that easy to grasp. While reading its source code, I stumbled upon a strange pattern: Storing the ServletRequest in a ThreadLocal.

I had not seen that before, and was wondering why one would do such a thing. It seems to be unintuitive. I found my answer through… GWT widgets. In this page, the author explain motivations behind doing such a thing:

While not 100% in tune with the MVC pattern, it is often convenient to access the servlet container, the HTTP session or the current HTTP request from the business layer. The GWT-SL provides several strategies to achieve this which pose a compromise in the amount of configuration required to set up and the class dependencies introduced to the business code. The easiest way to obtain the current HTTP request is by using the ServletUtils class which provides convenience methods for accessing the HttpServletRequest and HttpServletResponse instances. Please note that it makes use of thread local variables and will obviously not return correct values if used in any other than the invoking thread.

Still one can doubt if this is good design. In my long experience of web apps in Java I never had the need to do such a thing. Have you seen that pattern before?

Vim setup

Here is my Vim setup information for reference

in .vimrc or _vimrc, add at the beginning:
set langmenu=en_US.ISO_8859-1
set gfn=Bitstream_Vera_Sans_Mono:h9:cANSI
colorscheme oceandeep

First line is to avoid menus in French.
The font (you can find here) is simply the best programmer's font.
oceandeep mode can be found here .

Why Eclipse Is Better

Initially I adopted Eclipse instead of Emacs because it was more powerful to search code, and it allowed refactoring. I regularly tried other IDEs but always end up back to Eclipse, even though there has been less big improvements in Eclipse in the past years (but lots of small ones).

I just saw today that Eclipse allowed programmatic refactoring. Now that’s something quite amazing, and I don’t think other IDEs do that yet. Someone even had fun writing an Eclipse extension in Scala to add a particular kind of refactoring to Eclipse.

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