[news.eclipse.platform] Re: Plugin runs when launched from Eclipse, "cyc

[Matthew Hall <matthall@xxxxxxxxxxxxxxxxx>]

Irfan Hamid wrote:
> Hi,
>
> I have three different plugin projects in my workspace, e.g.: 
> com.name.prod, com.name.prod.unit1 and com.name.prod.unit2. 
> Unfortunately I have circular dependencies among these plugins. The main 
> plugin is com.name.prod, when I run it from within Eclipse as a plugin, 
> it runs and doesn't give me a problem. However, when I try to export it 
> using the plugin Export Wizard, it says "Problems during export. Reason: 
> A cycle was detected when generating the classpath com.name.prod, 
> com.name.prod.unit1, com.name.prod"
>
> I have tried removing the plugin dependencies among the projects and 
> instead putting the required packages as explicit dependant packages but 
> still no solution.
>
> I have tried adding and removing the .classpath file from the build 
> manifest of the plugins. Still the same problem.
>
> Any help would be highly appreciated.
>
> TIA,
> Irfan Hamid.

OSGi does not allow circular dependencies.  At least not directly.  I 
see three main options:

1) Merge the plugins that depend on eachother into a single plugin.

2) If the interaction between them is at arms length (i.e. by 
Class.forName(String) and reflection rather than direct references to 
class names) you may be able to do this using a buddy policy:

Let's assume that com.name.prod is the main module and is not directly 
aware of prod1.  Add the following to com.name.prod's manifest:

Eclipse-BuddyPolicy: registered

Now, in com.name.prod.unit1, which has com.name.prod as a dependency, 
add the following to the manifest:

Eclipse-RegisterBuddy: com.name.prod

By doing this, com.name.prod's classloader will be able to get at any of 
com.name.prod.unit1's exported packages, using the Class.forName(String) 
method.  However com.name.prod, since it does not have 
com.name.prod.unit1 as a dependency, cannot directly reference any of 
unit1's classes in code.

3) Create an extension point in com.name.prod and allow 
com.name.prod.unit1 and com.name.prod.unit2 to add extensions to that 
extension point.  I unfortunately can't help you with this one, since 
writing extension points requires writing an XML DTD, which I've never 
figured out.

Good luck.

Matt