Posts Tagged ‘java’

Proving Java Terminates (or runs forever) – Avoiding deadlock automatically with compile time checking

Tuesday, October 12th, 2010

This is one of the two projects I was considering doing for my Part II project and the one which I decided not to do.
This project would involve using annotations in Java to check that the thread safety properties which the programmer believes that the code has actually hold.
For example @DeadlockFree or @ThreadSafe.
Now you might think that this would be both incredibly useful and far too difficult/impossible however implementations of this exist at least in part: The MIT licensed CheckThread project and another implementation forms part of the much larger JSR-305 project to use annotations in java to detect software defects. JSR-305 was going to be part of Java 7 but development appears to be slow (over a year between the second most recent commit and the most recent commit (4 days ago)).

Essentially if you want to use annotations in Java to find your thread safety/deadlock bugs and prevent them from reoccurring the technology is out there (but needs some polishing). In the end I decided that since I could probably hack something working together and get it packaged in Debian in a couple of days/weeks by fixing problems in the existing implementations then it would not be particularly useful to spend several months reimplementing it as a Part II project.

If a library which allows you to use annotations in Java to prevent thread safety/deadlock problems is not in Debian (including new queue) by the end of next summer throw things at me until it is.

Packaging a java library for Debian as an upstream

Tuesday, August 17th, 2010

I have just finished my GSoC project working on GNU Prolog for Java which is a Java library for doing Prolog. I got as far as the beta release of version 0.2.5. One of the things I want to do for the final release is to integrate the making of .deb files to distribute the binary, source and documentation into the ant build system. This post exists to chronicle how I go about doing that.

First some background reading: There is a page on the debian wiki on Java Packaging. You will want to install javahelper as well as debain-policy and debhelper. You will then have the javahelper documentation in /usr/share/doc/javahelper/. The debian policy on java will probably also be useful.

Now most debian packages will be created by people working for debian using the releases made by upstreams but I want to be a good upstream and do it myself.

So I ran:

jh_makepkg --package=gnuprologjava --maintainer="Daniel Thomas" \
    --email="" --upstream="0.2.5" --library --ant --default

I then reported a bug in jh_makepkg where it fails to support the --default and --email options properly because I got “Invalid option: default”. Which might be fixed by the time you read this.
So I ran:

jh_makepkg --package=gnuprologjava --maintainer="Daniel Thomas" \
    --email="" --upstream="0.2.5" --library --ant

And selected ‘default’ when prompted by pressing F.
I got:

dch warning: Recognised distributions are:
{dapper,hardy,intrepid,jaunty,karmic,lucid,maverick}{,-updates,-security,-proposed,-backports} and UNRELEASED.
Using your request anyway.
dch: Did you see that warning?  Press RETURN to continue...

Which I think stems from the fact that javahelper is assuming debian but javahelper uses debhelper or similar which Ubuntu has configured for Ubuntu. However this doesn’t matter to me as I am trying to make a .deb for Debian (as it will then end up in Ubuntu and many other places – push everything as far upstream as possible).
Now because of the previously mentioned bug the --email option is not correctly handled so we need to fix changelog, control and copyright in the created debian folder to use the correct email address rather than user@host in the case of changelog and NAME in the case of control and copyright (two places in copyright).

copyright needs updating to have Upstream Author, Copyright list and licence statement and homepage.
For licence statement I used:

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 3 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA  02110-1301 USA

On Debian systems the full text of the GNU Library Public License, can be
found in the file /usr/share/common-licenses/LGPL-3.

control needs updating to add homepage, Short Description and Long Description (which needs to be indented with one space). I also added texinfo and libgetopt-java to Build-Depends and Suggests: libgetopt-java.
GNU Prolog for Java has a build dependency on gnu.getopt as gnu.prolog.test.GoalRunner uses it so I added
export CLASSPATH=/usr/share/java/gnu-getopt.jar to debian/rules. libgnuprologjava-java.javadoc needed build/api put in it so that it could find the javadoc.

So at this point I have a debian folder with the right files in it but I don’t have an ant task which will do everything neatly. Since debian package building really wants to happen on an unpacked release tarball of the source I modified my existing dist-src target to copy the debian folder across as well and added the following to my init target:

<!-- Key id to use for signing the .deb files -->
<property name="dist.keyid" value="" />
<property name="" value="${}-${version}"/>
<property name="dist.debdir" value="dist/${}/" />

I could then add the following dist-deb target to do all the work.

<target name="dist-deb" depends="dist-src" description="Produce a .deb to install with">
	<mkdir dir="${dist.debdir}"/>
	<unzip src="dist/${}" dest="${dist.debdir}"/>
	<!-- Delete the getopt code as we want to use the libgetopt-java package for that -->
	<delete dir="${dist.debdir}src/gnu/getopt"/>
	<exec executable="dpkg-buildpackage" dir="${dist.debdir}">
		<arg value="-k${dist.keyid}"/>

So this gives me binary and source files for distribution and includes the javadoc documentation but lacks the manual.
To fix that I added containing


, containing build/ and libgnuprologjava-java.doc-base.manual containing:

Document: libgnuprologjava-java-manual
Title: Manual for libgnuprologjava-java
Author: Daniel Thomas
Abstract: This the Manual for libgnuprologjava-java
Section: Programming

Format: HTML
Index: /usr/share/doc/libgnuprologjava-java/manual
Files: /usr/share/doc/libgnuprologjava-java/manual/*.html

Now all of this might result in the creation of the relevant files needed to get GNU Prolog for Java into Debian but then again it might not :-). The .deb file does install (and uninstall) correctly on my machine but I might have violated some debian-policy.

Postgres, ResultSets and Concurrency

Monday, February 15th, 2010

I thought I had found a concurrency bug in PostgreSQL because a ResultSet that was local to a method was being closed by activity occurring in a different thread.

Then I read: “Once you make another query with the Statement used to create a ResultSet, the currently open ResultSet instance is closed automatically.” on

Which means that I will have to make my code slightly less concurrent to work around that :-(.

I suspect it prevents bad coders from causing resource leaks though. So it is probably a good design decision.

This is why your unit tests should check for concurrency flaws :-).