Clojure: TCO + Memoization

Here's how to get around another rough edge in Clojure.

Expressiveness (2)

Transposing a matrix in Clojure:

(defn transpose [m]
  (apply mapv vector m))

(from http://stackoverflow.com/a/10347404/1144274)

Remote VisualVM

In my current project at work, I need to do some profiling on a Java app that runs on a server. Hooking it up to my local VisualVM (awesome tool, btw) was not immediately obvious to me, so here's the steps:

Prepare application on remote server

jstatd needs some security settings explained in [1]. Open vim, enter

grant codebase "file:${java.home}/../lib/tools.jar" {

  permission java.security.AllPermission;

};

and save as jstatd.all.policy.

Now start jstatd in the same directory, let in run in the background:

jstatd -J-Djava.security.policy=jstatd.all.policy &

Next, start the app (assuming $MY_APP is the main class) as described in [2]:

java \

 -Dcom.sun.management.jmxremote \

 -Dcom.sun.management.jmxremote.port=$JMX_PORT \

 -Dcom.sun.management.jmxremote.ssl=false \

 -Dcom.sun.management.jmxremote.authenticate=false \

 -Djava.rmi.server.hostname=$EXTERNAL_IP \

 $MY_APP

$JMX_PORT can be any available TCP port. $EXTERNAL_IP is the server's external IP address.

Make sure that the server's firewall allows incoming connections on both TCP 1099 (jstatd) and the port you chose as $JMX_PORT.

Connect VisualVM

Start VisualVM, double click on remote. Enter the server's external IP address:

Right-click on the new connection and add a JMX connection:

Enter $EXTERNAL_IP:$JMX_PORT from above, in my case 192.168.0.160:

This should add a connection to the running app:

Double-click on it, start profiling, enjoy.

References

[1] http://dbafusion.blogspot.de/2010/05/jstad-error-could-not-create-remote.html

[2] http://jremoterun.sourceforge.net/startingJmxConnector.html

Tool Time

In this post I'll collect little things that make life easier.

Shell

https://github.com/robbyrussell/oh-my-zsh