Paul Bilnoski: On Exception Management

3. January, 2011

If you want to widen your understanding of exceptions and how to handle them, you should read Paul Bilnoski’s post “On Exception Management”

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Posted by digulla

Need something in SWT?

2. January, 2011

When the guys at SWT can’t be bothered, there is now an alternative: A little project to create drop in replacements for stuff that you want in SWT. Check it out here.

In the same place, you can find a slightly modified version of StyledText. When I say “slightly modified”, then I mean “at the API level”. I’m currently heavily refactoring the code inside to make it maintainable and more easily extendable.

Some achievements from the latest hacking session:

  • It’s now possible to write tests that verify the rendering of StyledText
  • Bullets are managed and rendered in their own special classes. Same goes for StyleRanges. That reduced the size from 1’700 lines to just about 1’100 lines – not that much but a good start. This also means I can write tests that just check the management of StyleRanges – without bothering with a main loop, resource management, etc.
  • There are a bunch of helper methods to debug the model behind your text. They can dump the text in readable form.

What’s next? I’m really starting to think about turning StyleRange and TextStyle into independent classes. Right now, the former inherits from the latter which means there is some really ugly code when it comes to reusing styles, merging styles, font handling, etc. One effect is that the current implementation violates the contract of equals() and hashCode(): equals() takes the range into account while hashCode() doesn’t. While that may not have an effect (StyleRanges with the same style just pile up in a hash map), it’s still a sign of a skewed API.

The API would be much more clean if there was a style manager (which you could dispose to free all fonts, colors, etc, at once) and when StyleRanges were just tiny classes that contain a range and a pointer to a style. That would allow to get rid of the ranges int array, we could use Set and List to manage style ranges, etc.

Something that I’ve been testing is hierarchical styles (i.e. styles that inherit from other styles). Works like in word processors where you define a basic style and then derive from that. I’m not happy with the performance right now but I’ve got some ideas.

How to use my version? Simple: Clone the StyledText project and install it. Check the POM to see which dependencies you need in your project. Now replace 

import org.eclipse.swt.custom.*;

with

import de.pdark.styledtext.*;

That’s it.

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Posted by digulla

Who is codebix.com?

30. December, 2010

Since a few days, I got pingbacks from codebix.com. Their site contains a lot of links to a lot of blogs but no real added value as far as I can tell … who are those guys? What’s their game?

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Posted by digulla

Pestered by deadlocks?

30. December, 2010

Serge Beauchamp wrote a tool to automatically locate and report places where they can occur: Freescale’s Deadlock Preventer is now released!

Details can be found in this blog post.

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Posted by digulla

Another lesson in performance: NIO

29. December, 2010

Remember when I wondered how slow it is to copy data around in memory?

This time, I needed to load a 2MB file from disk and examine it for certain patterns.

The original from jazzy spell checker worked like this: It did a binary search in the file for a code. The code would be at the start of each line and be separated from the correct word by an asterisk: 

    AT*wide
    AT*widow
    AT*width
    AT*wight
    AT*wit

The search algorithm would seek somewhere in the file, skip the current line, read the next one, compare the code against the one we look for. If our code was smaller, we would seek backward; if it was larger, we would seek forward. Standard binary search.

Only it didn’t work. The test took 4 seconds to load the file without finding anything. Debugging recursive algorithms isn’t as nice as looking at them …

So I considered a different approach: I would load the whole file, character by character, and remember the lines with the same code in an index. A good time to have a look at NIO, especially the grep example.

Question: If it takes 4 seconds to seek ten times in a RandomAccessFile and read about 2000 bytes from it, how long would it take to read it character by character, examine each line, build an index and then load whole chunks (say, 1KB each) from the file when a word needs to be looked up? Plus the additional work of removing the code pattern from the chunk to produce a list of words …

Answer: 0.3 seconds. That’s more than ten times faster. And I could probably optimize the code some more.

Conclusion: When it comes to performance, measurement beats superstition.

And the new code is easy to understand, and to test, too! ^_^

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Fixing problems in models

29. December, 2010

MDD is nice as long as you don’t have exceptions. If you generate 1,000 classes and then one of them needs something special, you’re in trouble.

I think support for applying patches to the result of the code generation step would be a nice feature.

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Posted by digulla

Java tip: Getting most out of exceptions

28. December, 2010

Exceptions should have two purposes: 1. Clean up after an error and 2. help you solve the issue. Sadly, many Java developers often forget about #2.

So you end up with an exception thrown in SignatureFileVerifier (no source). Or even in a native method. The error message is:

Invalid signature file digest for Manifest main attributes

Right. Which tells us exactly … nothing. The stack trace isn’t better:

java.lang.SecurityException: Invalid signature file digest for Manifest main attributes
	at sun.security.util.SignatureFileVerifier.processImpl(SignatureFileVerifier.java:221)
	at sun.security.util.SignatureFileVerifier.process(SignatureFileVerifier.java:176)
	at java.util.jar.JarVerifier.processEntry(JarVerifier.java:233)
	at java.util.jar.JarVerifier.update(JarVerifier.java:188)
	at java.util.jar.JarFile.initializeVerifier(JarFile.java:325)
	at java.util.jar.JarFile.getInputStream(JarFile.java:390)
	at sun.misc.URLClassPath$JarLoader$1.getInputStream(URLClassPath.java:620)
	at sun.misc.Resource.cachedInputStream(Resource.java:59)
	at sun.misc.Resource.getByteBuffer(Resource.java:84)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:249)
	at java.net.URLClassLoader.access$100(URLClassLoader.java:56)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
	at org.eclipse.jface.action.LegacyActionTools.initLocalizedModifiers(LegacyActionTools.java:699)
	at org.eclipse.jface.action.LegacyActionTools.findLocalizedModifier(LegacyActionTools.java:356)
	at org.eclipse.jface.action.LegacyActionTools.convertLocalizedAccelerator(LegacyActionTools.java:167)
	at org.eclipse.jface.action.Action.setText(Action.java:665)
	at de.pdark.epen.editor.actions.ForwardAction.(ForwardAction.java:29)
	at de.pdark.epen.editor.actions.ForwardActionTest.testCreate(ForwardActionTest.java:21)

So LegacyActionTools needs a class. Which one? Since I don’t have the source, how can I set a breakpoint?

Simple: Set the breakpoint in the constructor of the exception! Even native code has to pass through here, eventually.

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Posted by digulla

Java performance

27. December, 2010

James Sutherland: “Java performance optimization is part analysis, and part superstition and witch craft.”

In his blog post “What is faster? JVM Performance,” he compares various ways to solve problems in Java and how they perform. For example, how the various map types perform.

What surprised me as well was to poor performance of HashMap. 23% slower than Hashtable…

Another surprise that block synchronized code is twice as expensive as synchronized methods. Tools like FindBugs discourage using synchronized methods.

Or the impact of volatile on field access.

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Posted by digulla

Merry Christmas

24. December, 2010
Christmas in the post-War United States

Image via Wikipedia

Merry Christmas to you all 🙂

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Posted by digulla

Identifying you

22. December, 2010

You have a firewall, NoScript, disabled cookies and everything. Do you think you’re surfing anonymously?

Think again: http://panopticlick.eff.org/index.php

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Posted by digulla

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