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I was getting this error when running a Sonar analysis recently.

This was caused by the Jenkins/Sonar process getting killed while the project analysis is underway. Sonar now uses a database semaphore to prevent multiple builds running at the same time, but if the job gets terminated then the semaphores don’t get cleaned up.

To fix the problem: Log into the database and delete any rows in the ‘semaphores’ table.

Mercurial loads a bunch of different configuration files and overlays their values on top of each other. The hgrc man page shows the order in which these files are loaded.

I encountered an issue recently where I knew that hg was using an erroneous setting but I had no idea where the setting was coming from.

The magic answer is

hg --debug showconfig  

This will output all the current settings, along with the name of the file that it got each setting from. Very useful indeed.

When there’s a merge conflict in Mercurial, TortoiseHG will give you the option to ’take local’ or ’take other’ in addition to resolving the conflict.

However, sometimes you may want to ’take local’ or ’take other’ when there’s no merge conflict.

To take local:

hg merge --tool internal:local <rev>  

To take other:

hg merge --tool internal:other <rev>  

Given the following code

Map<String, String> map = new HashMap<String, String>();  
map.put("123", "value");

Integer key = Integer.valueOf(123);  
String actual = map.get(key);  

What is the value of “actual”?

1. Compilation error - key should be a String
2. “value”
3. null

Answer: null

This blew me away. The whole point of type-safe collections was supposed to provide compile-time checking. However, the only generics method on the Map class is put(K, V). So calling get(Object) doesn’t cause a compilation error, but merely returns null.

I recently set up a Mercurial server (Windows, Apache, ActiveDirectory and hgweb.wsgi). However, cloning our 1Gb repository took an hour or more and often failed.

The only information in the Apache log was

mod_wsgi (pid=1234: Exception occurred processing WSGI script
'C:/hg/hgweb/hgweb.wsgi'  
IOError: failed to write data  

The solution was to disable compression by adding the following lines to hgweb.config

[server]  
preferuncompressed = true  

By default, Mercurial will compress everything before sending it down the pipe. This makes sense if you have a powerful server and a slow network, but the opposite was true for us - Mercurial’s hosted on an old dual-core Windows VM connected to a 1Gb corporate LAN.

java.util.logging.ErrorManager: 4: Unable to create [c:pache-tomcat-7.0.30 -Dcatalina.home=c:pache-tomcat-7.0.30\logs\]

I was getting this error recently, and found that it was caused by having a trailing backslash on my CATALINA_HOME variable.

i.e.
Incorrect:

set CATALINA_HOME=c:pache-tomcat-7.0.30\

Correct:

set CATALINA_HOME=c:pache-tomcat-7.0.30

When I first started programming in object oriented languages I used inheritance to reduce code duplication. You know the deal - you have two classes that do the same sort of thing so you create an abstract superclass and extract the common code into methods in the superclass. Voilà. No more duplicated code.

But I was unwittingly creating an untestable codebase.

I have worked extensively with dependency injection containers over the last five years and have begun to rely on the clean code they facilitate. DI encourages loosely coupled classes and interface abstractions, so code re-use is typically achieved by extracting the common code into its own class and injecting that class as a collaborator.

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
[INFO] --- maven-dependency-plugin:2.1:tree (default-cli) @ junit-categories ---
[INFO] com.craigpardey:junit-categories:jar:1.0-SNAPSHOT
[INFO] +- org.jmock:jmock-junit4:jar:2.6.0-RC2:test
[INFO] |  +- org.jmock:jmock:jar:2.6.0-RC2:test
[INFO] |  |  \- org.hamcrest:hamcrest-library:jar:1.3.RC2:test
[INFO] |  \- junit:junit-dep:jar:4.4:test
[INFO] \- junit:junit:jar:4.10:test
[INFO]    \- org.hamcrest:hamcrest-core:jar:1.1:test

See how jmock-junit4 depends on junit-dep:4.4, and that it appears before JUnit 4.10? That’s the cause of the error above. You can either exclude each of these conflicting dependencies or you can make sure that the versions of JUnit and/or JUnit-dep appear first in the classpath. The latter is achieved by putting them at the top of the dependency list in your pom.xml (or better yet, the parent pom.xml if you have one).
Here’s the dependency tree after moving the JUnit dependency above the jMock dependency in my pom.xml

I find it hard to remember all the .hgignore settings for a new Mercurial repository that I need, so here’s a bootstrap version

syntax: glob
.hgignore
*/target/**
*/.settings/**
*/.classpath
*/.project
*.log
*.orig

There was no stand-up this morning and it felt like my day never really started. It was my first day at my new job with CIBC and, even though I knew that the team was not agile before signing up for the gig, I had underestimated how much I depended upon our daily rituals practices at Intelliware. These practices provided a rhythm and cadence to the day that I had taken for granted.