Weakly Reachable

... until the collector arrives ...

This "blog" is really just a scratchpad of mine. There is not much of general interest here. Most of the content is scribbled down "live" as I discover things I want to remember. I rarely go back to correct mistakes in older entries. You have been warned :)

2014-04-24

Hashing + Doubles = Sneaky Nondeterminism in a JUnit Test

One of our calculation unit tests would fail erratically. Most of the time, it would pass. But on some runs (one in five?) one calculated double value would mysteriously flip from 0.0 to -0.0. Floating-point numerical errors are well-known, but the nondeterminism was a surprise as we could not think of any random or time-based elements in our calculation.

The cause turned out to be missing hashCode()/equals() on an object that was placed into a map. In such cases, the identity hash is used. The identity hash is typically based upon a memory location or a handle identifier and, as such, can easily change from run to run. The entries in the map were being iterated over, but the changing hashes would cause the iteration order to change. Elaborately calculated values from each iteration were being summed, and the changing summation order would sometimes produce a -0.0 from an underflow.

The nondeterminism did not produce any material errors in the calculated results -- strictly speaking there was not a bug in the code. However, the intermittent failures of JUnit tests was unhelpful.

2014-04-13

Heartbleed Commit

Here is a link to the commit that introduced the Heartbleed OpenSSL Vulnerability.

2014-04-10

Eclipse OSGI - The Windows Virus

When Eclipse OSGI starts up, it checks to see whether certain locations are writable. Based on what it finds, it chooses locations for the configuration area, the user base directory, etc. What is "interesting" is the way that it determines whether a location is writable. Here is an excerpt from AdaptorUtil.java:

File fileTest = null;
try {
    // we use the .dll suffix to properly test on Vista virtual directories
    // on Vista you are not allowed to write executable files on virtual directories like "Program Files"
    fileTest = File.createTempFile("writtableArea", ".dll", installDir); //$NON-NLS-1$ //$NON-NLS-2$
} catch (IOException e) {
    //If an exception occured while trying to create the file, it means that it is not writtable
    return false;
} finally {
    if (fileTest != null)
        fileTest.delete();
}
return true;

The code attempts to create a file named writtableArea.dll in the target directory. This sets off alarm bells on many virus scanners. This came to my attention because exactly one of users reported that our RCP application would simply disappear after presenting the splash screen. They were using Kapersky with particularly draconian settings.

2014-01-08

Eclipse RCP vs. Changing a Perspective Name

Using Eclipse 3.7.2 or 4.3.1, I ran into a problem where I wanted to change the name of the perspective in an RCP application. I changed the title in the bundle.properties file and relaunched my application from within the Eclipse IDE. The title had not changed. My immediate thought was that the title was cached in the application workspace data. So I relaunched the application after changing the launch configuration to clear that data first. The old label remained. I cleaned and rebuilt the application projects. I exited and re-entered Eclipse. I shook my fist in frustration. None of these would make the label change.

A scan of all files within the IDE .metadata directly yielded a couple of binary files that contained the old string. After some head-scratching, it was determined that these files were in the application's configuration area. This can be cleared in the launch configuration by switching to the Configuration tab and ticking the Clear the configuration area before launching checkbox. After that, the new label took effect.

Blog Archive