Friday, December 26, 2008

Bug in Solaris JVM, forkAndExec

We've discovered a bug in the Solaris JVM that we're using (1.5.0_08-b03). What happens is that we have a long running JVM that once a minute forks an executable viajava.lang.Runtime.exec and reads its stdout. After a long time, one of the forks doesn't actually make it to the exec, and the thread that asked for the exec doesn't continue. That's why I think it's a JVM bug: the exec call is made and only completes half of its job.
I describe the problem on a Sun forum here.
I definitely have to upgrade the JVM to see if that helps...

Tuesday, December 23, 2008

Hibernate emits empty DDL file

This is the second time this has bitten me: I want to use Hibernate with standard JPA to persist my entities. And I want my Entities autodetected, as Hibernate is capable of, even outside of a JEE container. So in my persistence.xml I have this bit of code:
      <property name="hibernate.archive.autodetection" value="class,hbm"/>
But, I do not compile this persistence.xml into my .jar file, instead I just make it part of my classpath for my unit tests, thinking this will make things more flexible. And of course, this doesn’t work. The autodetection only works if the persistence.xml is located in the META-INF section of the jarfile that contains the Entities to be detected. See my post in the Hibernate forum.

JSF page based on Seam example not rendered

If you’re a JSF newbie (like me), and you’re using Seam, you might be tempted to take one of the examples and hack away at it. For instance, in the booking example, the first page is called home.xhtml. After you type up some tags, you want it to run, so you point your browser at:
What you’ll find is not a JSF rendered page, but your JSF tag source! Then you think that you’ve misconfigured something, so you look over everything. But what’s really going on is that the Seam example isn’t configured to render that page, instead you should go to:
That will render the home.xhtml as JSF. Look in your war file’s WEB-INF/web.xml, and find this bit of code:
    <servlet-name>Faces Servlet</servlet-name>
This means that the Faces Servlet logic executes against URLs that end with .seam. However, being a newbie, I’m not quite sure what maps that against the .xhtml file, unless it’s this previous entry:
Also being a newbie, I’m not sure what I should do to configure things so that it’s impossible for a user to download my JSF code…
Anyhow, what makes this all work by default is the file index.html, which is what will load when you visit:
and that contains the following:
    <meta http-equiv="Refresh" content="0; URL=home.seam">
which naturally redirects you to the appropriate URL to start rendering your JSF/Seam application.
Thanks to anyone who points out the answers to the above mysteries (that are probably in the docs somewhere…)

Thursday, December 18, 2008

Using JBoss AS and Seam

Things to do when using JBoss AS (4.2.3.GA) and Seam (2.1.0.SP1):

  • Download the latest (at least 1.8.0) commons-beanutils for your .ear. It fixes amemory leak you'd see after you redeploy your .ear.
  • If you're running on OS X, disable the unnecessary dock icon from JBoss by adding -Djava.awt.headless=true. This might also solve problems on Linux/Solaris boxes that you're ssh'd onto and you don't have a DISPLAY environment variable set for X Windows.
  • Use your own jboss-log4j.xml file, which by default is in${jboss.home}/server/default/conf/jboss-log4j.xml. You probably don't need DEBUG output emitted to your console...

Tuesday, December 16, 2008

OS X and Java SE 6

It appears that you can run Java SE 6 on a Mac, but only if you're Intel 64-bit. No PowerPC, no 32-bit Intel.

But from my terminal on a 64-bit Intel machine with all updates:

$ type java
java is /usr/bin/java

$ java -version
java version "1.5.0_16"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_16-b06-284)
Java HotSpot(TM) Client VM (build 1.5.0_16-133, mixed mode, sharing)

In order to get Java SE 6 running on your Mac, open the Java Preferences (at /Applications/Utilities/Java/Java Preferences) and drag Java SE 6 to the top of the list for Java applet versions and/or Java application versions. Now I get:

$ java -version
java version "1.6.0_07"
Java(TM) SE Runtime Environment (build 1.6.0_07-b06-153)
Java HotSpot(TM) 64-Bit Server VM (build 1.6.0_07-b06-57, mixed mode)

Note that you may not be very happy with the result... Given the history of Java support on OS X, perhaps I should try SoyLatte.

Friday, December 12, 2008

git is slow; too many lstat operations

I'm working on a new project and using git for the first time; I really like the distributed source control model, it makes a lot of sense. I come from using p4 for quite a long time, so git feels a lot like CVS/SubVersion, but obviously a lot more powerful than CVS. Also, I want to make sure that I do not say that git is hard to understand and use.

The way I work with my projects is by submitting not only all my source code for my project, but also all tools that are used to generate my project. (Obviously I draw the line somewhere, I don't submit my Linux distribution that I use on the build machine.) That way I can guarantee reproducibility and no one on the team has to install their own tools before being productive.

A short time into my new project I already have more than 500,000 files in my git repository. Now every time I use any git command, it just sits there for many seconds... even when I open a file using Emacs, I have a severe delay because git is invoked to check its status. Using dtrace I've determined that it is doing an lstat on every single file in the repository, to make sure that it's not out of date.

Therefore beware: git is not good for large repositories. And when I say large, I don't mean "sorta large" like 20,000 files. I mean more on the order of 500,000 or 2.5 million files (the current size of our p4 repository). This is because git is just like CVS: it automatically determines for you which files you have edited/deleted/added, and which you have not, but it does this by doing an lstat on every single file in your tree. p4 does not make this assumption, and requires you to tell it what files you have edited/deleted/added, therefore it never does an lstat of the files in your tree (unless you invoke some special commands to ask it to look).

It seems there are attempts to optimize the lstat operations, but it is part of the design of git, and would likely be unnatural to avoid it or suppress it.

I found the git benchmarks, where it describes how efficient it is for the size of its repositories, which is great. However, it does not mention the number of files in a repository. And I couldn't find the current size of the linux kernel repository, but I found a mention that the pull of an entire tree was 5,000 files, which included all of git's metadata (if I understood it correctly).

In order to work around git's slowness with large numbers of files, I decided to split my git repository into two halves; the half with the tools, and the other half with my project source. I found a tool called git split that seems to do the job (see, but it didn't work on my git 1.6.0 repository. It got stuck because it couldn't read my .git/info/grafts. So I gave up there and just deleted all the tools out of my tree, and added them into a separate git repository. That made things much better.

Update: I found this blog article that also claims that git does not scale: Why Perforce is more scalable than Git

Thursday, December 11, 2008

Hibernate JPA annotations work only on get method, not set

I have a project where I'm using Hibernate with JPA annotations. I got stuck where the annotations to one of my attributes wouldn't stick, but I finally figured it out:

You have to annotate either the member (in which case all attributes must be annotated via member), or the get method for your attribute. You can't annotate the set method.