Strange Loops

Compiling Jython Scripts to Java Class Files

Had this little snippet of code lying around my directory.

Didn't know what to do with it. It was somewhat useful. We were trying to compile unit tests written in jython for our java code. The jythonc tool had gone away in jython 2.5 but an ant task (JythoncAntTask) in 2.5 still did that. I did a little bit of code spelunking and extracted the code snippet seen above. I don't know the reasons for removal of jythonc but I suspect this usage is not generally supported by the jython maintainers. Please don't complain if this doesn't work for you. We went with another approach for getting our jython unit test to run.

One should be able to compile it from the command line. You'll need the jython.jar to compile it. To run this against a jython script, I threw together a little shell script.

This post was also a little experiment in embedding code samples into my blog posts. The trick is the script tags provided by gist do not work with the preview/rich text mode provided by typepad. They only work after the blog entry has been published. Other than this little gotcha,  Gist is a nice tool for collecting code snippets.

Building ØMQ on my Mac

In my plans for world domination, I need messaging software. I wanted to try out ZeroMQ (trying out RabbitMQ is for another weekend). I'm skipping ActiveMQ since we use it at work and I mostly understand what it provides.

Downloaded the tarball and it compiled right out of the box. However when I tried to get it to run with a simple java program I've written, I kept getting this error (this is on Leopard).

dc@feynman:dist$ java -Djava.library.path=/opt/personal/pkg/zmq/lib -classpath lib/Zmq.jar -jar ZmqTest.jar 
Creating ZMQ
Exception in thread "main" java.lang.UnsatisfiedLinkError: /opt/personal/pkg/zmq/lib/libjzmq.1.0.0.dylib: no suitable image found. Did find: /opt/personal/pkg/zmq/lib/libjzmq.1.0.0.dylib: mach-o, but wrong architecture /opt/personal/pkg/zmq/lib/libjzmq.1.0.0.dylib: mach-o, but wrong architecture
 at java.lang.ClassLoader$NativeLibrary.load(Native Method)
 at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1881)
 at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1805)
 at java.lang.Runtime.loadLibrary0(Runtime.java:823)
 at java.lang.System.loadLibrary(System.java:1045)
 at org.zmq.Zmq.(Zmq.java:25)
 at zmqtest.Main.main(Main.java:15)

As far as I can guess, the JVM I'm using is 64bit so the libraries it loads also need to be compiled as 64bits. To fix this, I had to set the CXXFLAGS environment variable to build 64 bits. This set of steps worked for me.

export CXXFLAGS="-arch x86_64" 
./configure --prefix=/opt/personal/pkg/zmq -with-java
make clean
make
make install

Here's my small java program

package zmqtest;
import org.zmq.Zmq;

public class Main {
 public static void main(String[] args) {
  System.out.println("Creating ZMQ");
  Zmq zmq = new Zmq("localhost");
  System.out.println("Done creating ZMQ");
 }
}

Oracle to Mysql Gotcha

At the new job, we use MySQL. I've mostly worked with Oracle before this and while not expecting everything to be the same, the transition has been smooth.

The one gotcha that threw me for a loop is MySQL's default transaction isolation level for. With Oracle, once data is committed, it's available to be read by all other connections. With MySQL, your view of data is determined by the first query made after the connection is open.

One rationale (I was given) is MySQL has fast connection setups and connections are setup and torn down between queries. I'm not sure I believe that though....

The solution was to change the isolation level for my session via the following incantation:

SET TRANSACTION ISOLATION LEVEL READ COMMITTED

(Taken from the mysql reference manual page)

virtualenv

One recent change to my life has been more python. Lots of nice/bad things have been said about the language that I won't repeat here. I'm generally enjoying my time with it. One useful tool I've found is virtualenv and its bash wrapper functions.

virtualenv allows me to create an environment (python + versioned set of packages) for me to work in. For example I have two virtualenvs right now (temp and django). "temp" contains a myriad number of different libraries I want to experiment with and "django" contains (well) django and a more limited set of libraries. To use I do "activate temp" or "activate django" from my shell depending on what I want to use.

I have a similar problem with perl. I have 2 versions 5.8.9 and 5.10 that I want to use. To take care of this, I have both perls compiled into two different locations. To switch working between the both of, I borrowed some inspiration from virtualenv.

#!/bin/sh
# use-perl5.10.sh
path-to/cpanp 's program perlwrapper path-to/perl5.10/bin/cpanp-run-perl; s save'
PATH=path-to/perl5.10/bin:${PATH} PS1="(5.10) \h:\W \u\$ " /bin/bash

#!/bin/sh
# use-perl5.8.sh
cpanp 's program perlwrapper path-to/bin/cpanp-run-perl; s save'
PATH=path-to/bin:${PATH} PS1="(5.8) \h:\W \u\$ " /bin/bash

I call use-perl5.8.sh and use-perl5.10.sh as appropriate from my shell to setup a working environment from perl. This doesn't isolate the libraries like virtualenv but switching between the two perls is all I needed for now.

Down the Language Rabbit Hole

Once more into the breach.... Been going down the functional languages rabbit hole again, this time I've been more patient with it. The thing about self learning is that you can take your time with it. I rushed through the Little Schemer the first time, this time I'm taking my time going through it and trying to understand the various nuances to programming with recursion. Here we go again.