Help! How to manage multiple (RCP) applications in one installation?

Maybe someone reading my blog can help me. I posted essentially the message below to the equinox newsgroup and the platform newsgroup with zero response. Maybe RCP in the headline will help getting someone to read my post ;-)....

How to restrict the plugins visible to an application?

We have several applications (some of them are headless) that run from within the same eclipse installation. The problem is, that all plugins are visible from the applications. This cause problems, if extensions are used that load plugins that cannot run in the context of the headless application.

To illustrate the problem I use a simple example. A headless application that uses the org.eclipse.core.variables plugin to expand a variable. The org.eclipse.core.variables is UI free and therefore no problem. But some plugins that contribute to the variables plugin are not headless. To illustrate this, I use the ${selected_text} variable that is defined in the org.eclipse.debug.ui plugin. This causes the application to fail.

  public class MyApplicationWithVariables implements IPlatformRunnable {
    public Object run(Object arg) throws Exception {
      IStringVariableManager vm=VariablesPlugin.getDefault().getStringVariableManager();
      String message=vm.performStringSubstitution("Hello ${selected_text}!");
      System.out.println(message);
      return EXIT_OK;
    }
  }

   <extension
         id="HelloWorldWithVariables"
         name="Minimal Headless with variables"
         point="org.eclipse.core.runtime.applications">
      <application>
         <run class="gr.scharf.minimal.headless.MyApplicationWithVariables"/>
      </application>
   </extension>

Is there a way to restrict the plugins visible or loadable to an application?
Or is the only way to have a copy of the installation containing only the "good" plugins?

Michael

How the eclipse update manager could look like...

One of the features I don't like about eclipse is the update manager. A few weeks ago, I looked at different alternatives of eclipse update managers. Today Chris Aniszczyk blogged about the FireFox update manager. Interestingly, a few days ago, I created a small flash video on the FireFox update manager, because I think that shows what a user expects from a simple to use update manager.

One of the central paradigms of eclipse the idea of plugins. However from a user perspective, managing plugins is a nightmare. The eclipse update manager is way too complicated, too slow, not robust enough.

Few weeks ago I bought Eric Evans book "Domain Driven Design". I'll blog about it separately. One of the central ideas is what he calls "ubiquitous language" (e.g. read chapter one). The basic idea is to come up with a language to describe the problem domain, in our case the installation and update of plugins. The language is not only used in conversations but also represented by a formal model. The formal model is implemented in code. You can start reasoning and discuss about the model.

If I look at the eclipse update manager, the model used is a very technical model that is totally implementation centric. It is not a model a user of the update manager can simply understand. I think this is the root of the problem. We have to come up with an update manager domain model that represents the problems and tasks a user of eclipse faces and not a model that is focused on the implementation. The current implementation could be used to implement the user model, but in it self it seem not the right abstraction for users.

The FireFox update manager has an easy to understand domain model that is shown in the UI. There are extensions. An extension has an icon, a description and a set of preferences (yes the preferences of each extensions is available directly from the "Extensions" dialog. In eclipse there's no way to find out what an extension contributes to eclipse. See my blog entry "When seamless integration becomes a nightmare..."). Anyway, hit a simple button to check for updates. It's done in seconds (not minutes like eclipse). Once downloaded, you can update the plugins you want to update.

If you don't like an extension you can select an extension and "Uninstall" it. Something that is not possible with the eclipse update manager. Eclipse is a grow only system -- no way to remove features. Like windows in the old days. Once you have installed a feature there's no way to get rid of it. Only, if you regularly do backups (like I do), you can revert a previous version of eclipse by reverting a backup. But eclipse itself is grow only (*). If you have installed a few features you don't like and you cannot get rid of, you will start thinking twice if you want to install a new plugin. That's very bad for the eclipse ecosystem.

Eclipse must solve the update manager problem soon and provide a simple to use and understandable update manager that solves the problems of eclipse users.

Domain Driven Design could help come up with a update manager domain model that is relevant for eclipse users...

Michael

(*) You could also use separate extension locations for each feature you install and simply delete the location if you want to uninstall the extension. But that's a hack. The update manager (UI) does not even support dropping of extensions. I tried that for a while, but it requires a lot of discipline.

When a system becomes corrupt....

Have you ever had a system running stable for years and suddenly everything goes wrong?

It started last Saturday, when one of my usb-backup drives died. No big deal. I have two external backup drives with at most one attached to my system. I do weekly full backups and daily incremental backups on important data. I swap drives from time to time (I should swap them every day) and keep some old backups.

On Monday my DSL connection died. No problem, I have a ISDN USB modem I can use in those cases. The modem was cheap but the driver sucks: it uses 100% CPU even if nothing is going on. Well, no problem, I downloaded a new driver, created an XP system restore point and installed the driver. Well, I tried different versions of the driver. No one really helped, the last one crashed my system. OK, I did a "system restore", but during shutdown the driver crashed my computer. Restart, login ... baang! Windows forgot my user settings! It created a new profile. All settings lost!

No problem, I first create a backup (it's always a good idea to backup the entire system, even if is corrupt, before you mess around!) and then I wanted to back the last full backup...

Big problem! The last backup is corrupt, and the most recent backups are on my dead drive...

...for the last 12 hours I have been playing back different versions of backup trying to restore my user data. In between I have between googling for the potential problem of my setup, with little success. Whenever I restored my latest user data in C:\Documents and Settings\<username>, windows decided to create a new profile for me. I got very very frustrated and finally accepted the fact that I have to live with a new profile and I have to set up my environment from scratch. I copied all my user data into the new profile....

...Firefox, Thunderbird, cygwin, eclipse are applications that did not loose data and were running as before. But my desktop, internet explorer and many other applications that depend on the registry lost their settings. The worst case was Outlook, it wants to be reinstalled and looses all setting that are not on the exchange server...

So, I asked myself, is there a way to get my personal registry settings into my new profile? Finally I stumbled over the important files: the C:\Documents and Settings\<username>\ntuser.* files. From my "after the problem" backup I figured out that the file ntuser.dat file was missing.

Was that the key to my problem? Did loosing the ntuser.dat cause all the troubles? Ok, I had to try it. I copied an old version from a backup into my corrupt profile. Hmm, but how to tell XP to use my old profile directory again? A quick search in the registry revealed that the profile directory is stored under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList/*. I changed it, renamed my new profile to something else and restarted....

WOW! It works. My system is back. Outlook works, my desktop looks like always, all applications work as expected. I'm happy again....

What has my windows problem to do with eclipse?

Eclipse does not use the registry, but it has the magic .metadata directory. Over the last 5 years my .metadata directory got corrupt several times. If something goes wrong with the ..metadata (like running out of disk-space), it's very hard, if not impossible, to recover from that. You can, similar to windows, create a new workspace and import the projects. But then you have lost a lot of settings and you "start from scratch". My backups saved me several times here.

Conclusions

• Backup the corrupted system before you do anything.
  
• Make bakups. Regularly!

Michael

Mylar is very cool, however sometimes it drives me nuts...

Mylar is an eclipse technology project. It makes it easy to focus on a task you are working on, by hiding the information that's not relevant to the current task.

How does it know, which information is relevant? It "looks over your shoulder" and remembers the files, classes and methods you have looked at. With some magic it puts some weight on the places you have been. For example if you get back to some place or even edit there, it gets more weight than just looking once at the file. But you can also tell mylar explicitly that you are interested or not interested in some context.

How does it hide irrelevant information? Well, in the package explorer, outline etc you see only the classes and methods in your context. There's even a mode that shows the relevance by the background color. And really important places are shown in bold. To build up context, you can disable mylar on the view to see everything. I never use the editor folding features of mylar, because I don't like folding.

If you want to learn more, I highly recommend the getting started flash demon.

There are also integrations with bug tracking systems, and it seems that this is how most people are using Mylar. Unfortunately, we use a commercial bug-tracking system that is not supported by mylar. But I find mylar very useful, even without the bug tracking system integration.

However, sometimes I hate mylar: I am working on a problem, and I find something interesting I want to look at later. So, I create a new mylar task. That's all fine. But now, when I want to add context to this task, I have to start from scratch, because mylar closes all my editors and collapses all my trees. However, if I have switched off mylar (that is: I have no active mylar task), and then create a new task and activate that new task, everything is good. In this case mylar does not close all my editors, but is clever it letting me build up my context from where I am. (I created a little flash demo to illustrate this workflow). I talked about this on the newsgroup, and it seems that my workflow is very special. I wonder if I am the only one having this workflow problem with mylar, therefore I created a bugzilla entry: bug 157933....

Don't swallow InterruptedException. Call Thread.currentThread().interrupt() instead.

Have you ever written the following code?

try {
    doSomething();
} catch(InterruptedException swallowed) {
    // BAD BAD PRACTICE, TO IGNORE THIS EXCEPTION
    // just logging is also not a useful option here....
}

I have! I newer knew what the heck to do with those annoying InterruptedException when I simply wanted to call Thread.sleep(..). What is this InterruptedException? Why is it thrown? Why can't I ignore it?

Before I explain the whys, here is what you should do (if you don't re-throw):

try {
    doSomething();
} catch(InterruptedException e) {
    // Restore the interrupted status
    Thread.currentThread().interrupt();
}

What is the InterruptedException?

There is no way to simply stop a running thread in java (don't even consider using the deprecated method stop()). Stopping threads is cooperative in java. Calling Thread.interrupt() is a way to tell the thread to stop what it is doing. If the thread is in a blocking call, the blocking call will throw an InterruptedException, otherwise the interrupted flag of the tread will be set. A Thread or a Runnable that is interruptable should check from time to time Thread.currentThread().isInterrupted(). If it returns true, cleanup and return.

Why is it InterruptedException thrown?

The problem is that blocking calls like sleep() and wait(), can take very long till the check can be done. Therefore they throw an InterruptedException. However the isInterrupted is cleared when the InterruptedException is thrown! (I have some vague idea why this is the case, but for whatever reason this is done, that is how it is!)

Why can't InterruptedException be simply ignored?

It should be clear by now: because ignoring an InterruptedException means resetting the interrupted status of the thread. For example, worker threads take runnable from a queue and execute they may check the interrupted status periodically. If you swallow it the thread would not know that it was interrupted and would happily continue to run.

Some more thoughts
Unfortunately it is not specified that Thread.interrupt() can only be used for cancellation. It can be used for anything that requires to set a flag on a thread. So, ending your task or runnable early might be the wrong choice, if the interrupted status is used for something else. But common practice is to use it for cancellation. But even if it is used for something else, you code does not have the right to reset the interrupt flag (unless you are the owner of the thread).

To learn more read the nice article Dealing with InterruptedException by Brian Goetz.

Or read Java Concurrency in Practice By BriaBrian Goetz, Tim Peierls, Joshua Bloch, Joseph Bowbeer, David Holmes, and Doug Lea. It's a great book! If you program in java 5 this book is a must read!. I bought the book after I read Brians artikle. I have not yet read the entire book, but what I have read impresses me. It gives a lot of theorie and options. Very competent and complete, but I'm missing a set of simple patterns for concurrent programming. I'm looking forward to Doug Leas 3rd edition of Concurrent Programming in Java

Summary: If you don't know what to do with an InterruptedException call Thread.currentThread().interrupt()

Pitfalls of Long.parseLong/Long.decode...

What is wrong with this code?

assert 0x0cc175b9c0f1b6a8L == Long.parseLong("0cc175b9c0f1b6a8",16);
assert 0xd41d8cd98f00b204L == Long.parseLong("d41d8cd98f00b204",16);

The second Long.parseLong will fail in the second line:

java.lang.NumberFormatException: For input string: "d41d8cd98f00b204"

The reason is that javas long is signed, but 0xd41d8cd98f00b204L is an unsigned long. Interesting, but annoying, if you want to parse an unsigned long in java. It makes Parsing and verifying hex, octal and decimal numbers more complicated, if you have a field that represents a C/C++ unsigned long (a 64 bit number)....

The solution is to use BigInteger:

assert 0x0cc175b9c0f1b6a8L == new BigInteger("0cc175b9c0f1b6a8",16).longValue();
assert 0xd41d8cd98f00b204L == new BigInteger("d41d8cd98f00b204",16).longValue();

However, you must ensure that the BigInteger does not exceed 64 bits. So here's my unsigned long parser

public static long parseUnsignedLong(String s, int radix) 
    throws NumberFormatException {
    BigInteger b= new BigInteger(s,radix);
    if(b.bitLength()>64)
        throw new NumberFormatException(s+" is to big!");
    return b.longValue();
}

Note: if you want to do any kind arithmetic with unsigned longs (like min/max checking) you have to use BigInteger objects.... Unless you are only interested in the bits of the long, the return value of my parseUnsignedLong is not really useful: it should better return the BigInteger!

The Dependency Injection Pattern: an alternative to Factories and Service Locators

On my vacation I listened to about 30 pod-casts. Although most of what I heard was not new, it still was a good refresher and exciting to listen to. It also inspired me to order a few books and make me think more about what I am doing as software engineer.

One pattern that was new to me is Dependency Injection. It was mentioned in software engineering radio Episode 2 on Dependencies. Instead of using a Factory or a Service Locator (like OSGi), make your class have some members referring to the interfaces it uses. The Dependency Injector then uses either the constructor or some set methods to provide your class with the implementations of the classes your object needs. Read the One minute description and the Two Minute Tutorial of PicoContainer (a nice little Dependency Injection Framework) to see what I mean.

Martin Fowler wrote a long article about Inversion of Control Containers and the Dependency Injection pattern.

I was always wondering why using interfaces when you have only one implementation of the interface anyway. So, why bother? With Dependency Injection you can test your object easyly using Mock Objects. Jeremy Weiskotten wrote an Dr.Dobb's Article on why Dependency Injection is very helpful to create testable and decoupled objects.

Dependency Injection makes it very clear which interfaces your objects depend on. This makes refactoring, testing and understanding code easier. Factories and Service Locators often provide more products than needed by a single class and therefore you cannot really tell what the class depends on.

I'll play with Dependency Injection :-)

Going on vacation with a mp3 player full of geek pod-casts...

I'm going on vacation for two weeks to Athens and Crete. My wife is Greek and therefore we go every summer to Greece. Going on vacation also means no laptop (that's not my deceison ;-). So usually, I take some geek books with me. This time I loaded my mp3 player with the 9 Callisto pod-casts from Eclipse Zone and a few of the Software Engineering Radio pod-casts.
I tried it on Friday. It's a almost like being in a conference call. But it's better: I can wind back if I get sidetracked and I don't have to be afraid that suddenly someone says: "And Michael, what do you think?....". I was shopping and listening to Richard Gromback on GMF. I was waiting in the queue to pay and when it was my turn, I started talking in English to the German cashier -- lost in cyberspace...

One thing I think pod-casts should do: Please say at the beginning of the pod-cast when it was recorded! If someone says: "Next month we'll release foobar..." it is annoying not to know when next month is or was...

And now, relaaaaaxxx, summer, sun, beach, fun -- for 2 weeks -- I'll be back Sep.5 late afternoon....

Blog comments, my mistakes and good feedback...

Marko Schulz asked me why his comments did not appear in my blog. I checked it and I realized that I had a setup problem with my blog (my mistake). Now all comments are visible and new comments will be shown automatically! I'll check them for spam later.

Here's what I learned from the comments:

• Parsing and verifying hex, octal and decimal numbers...: Several commenters pointed out that I should have used Long#decode(String) and therefore I adjusted the blog entry (and my code ;-).
  
• Am I the only person having problems with the update manager? The answer is clearly: no!
  
• Eclipse was hanging my machine regularly -- solution -XX:MaxPermSize=128m Surya asked if the -XX:MaxPermSize=128m can be put into the eclipse.ini files: the answer is yes.
  
• Why is super.super illegal? is the most debated. Lots of good reasons why super.super is illegal -- but from practical point of view it is annoying...
  
• I hate ClassCastExceptions...Marco said its fixed in 1.5 (ClassCastException is reporting the actual type of the object). I just made a test and it is true: even if compiled with 1.4 and run with 1.5 I see the ClassCastException reporting the type. I'm a bit puzzled why I don't see it in my applications -- I thought I'm using a 1.5 jre.
  
• How to setup some plugins to use java 1.5 in a java 1.4 workspace? Neil Bartlett pointed out that step 3 (Setting the execution environment in the build path to J2SE-1.5) is not needed. I tested it and it is needed. Le ScaL pointed me to an article on execution environment in the eclipse wiki.
  
• Update manager battle: the players Yoxos - YUM - eclipse... Wassim Melhem asks why I like yoxos though I have not seen it in action. Hmm, maybe I'm biased because its German and I know the guys or maybe because I spent some money on it and therefore it "has to be good" ;-). I hope to see an update soon....
  
• How far are the hotels from the eclipse summit October 11-12 2006 in Esslingen/Stuttgart Germany? Gerd Castan suggested to search search hotel.de. Good idea!
  

I checked all comments and I found a few spams, but most comments brought up valid points. Thank you for your feedback!

MDSD/MDA framework openArchitectureWare 4.1 is available at eclipse.org

I just read the announcement that openArchitectureWare 4.1 is available. openArchitectureWare is hosted at eclipse.org/gmt/oaw. It is one of the coolest projects at eclipse.org but it seems not to get much attention. If you are interested in MDSD or MDA take a look at openArchitectureWare - openArchitectureWare is really cool!