[oscar-devel] Instantiation deadlock: A bug?

[Rob W. <ro...@as...>]

Manuel

Excuse me if this has already been answered - I only get the list digests, which come out a little delayed.


>We 've got bundle A and B. Bundle B has got a class C, which he exports,
>and bundle A imports it. 
>
>  
>
That part should be fine, it's the way OSGi is intended to work

>Suppose A is already started. Now we start bundle B. In its activator,
>it contacts bundle B via RMI and tells him to instantiate class C (by
>reflection). The problem is that while bundle B is starting, bundle A
>cannot instantiate classes exported by bundle B. Usually, this is not a
>problem, because the call just waits until bundle B finishes starting.
>But in this case, a deadlock occurs, because bundle B won't finish until
>bundle A instantiates that class, and A won't instantiate that class
>until bundle B finishes. 
>
>  
>
First and foremost, this sounds like a logic/coding deadlock to me. It 
seems you have a mutual dependency in your startup logic:

- Bundle B needs Bundle A to do something before it can finish starting
- Bundle A needs to load classes from Bundle B before it can finish 
starting.

If I've understood this correctly, the only way you can break this 
deadlock is:

- remove one of the dependencies e.g. let Bundle B start without any 
dependency on Bundle A. Sort out what Bundle B needs later, such as by 
using Services and have Bundle B wait for the required services to 
become available.

- move the offending Class C (and any other dependent classes) into a 
pure "library" bundle that has no activator or active code, but just 
purely acts as a class library exporting classes for other bundles to 
use. Both Bundle A and Bundle B can then import these classes

-- Rob