The document discusses challenges in bundle updates with verified compatibility in OSGi, particularly issues related to versioning mismatches and runtime failures. It presents a version generator for creating correct version identifiers and a safe bundle update process that ensures compatibility checks during updates. The author highlights the importance of improved version management and type-safe updates for better OSGi application reliability.

1. 22nd June 2009, Zurich
Bundle Updates with
Verified Compatibility
Premek Brada
University of West Bohemia
Pilsen, CZ

2. Agenda
• Problems addressed
• Version generator
• Safe bundle update
• How does it work
• Experiences
OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 2

3. Problem addressed:
version id  implementation
reality mismatch
• Scenarios When you only import packages and require
some minimal or maximal version it means
– origin that the developer of the library has to do
very good version management. If he changes
– consequences an api and does not change the major number
it can affect an already deployed application.
• Variants With maven you already have the same
problems it compile time but with osgi it can
– false positives/negatives crash at runtime. We need a whole set of new
tools for this problem.
-- comment on Peter Krien’s blog, 6/2009
OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 3

4. Scenario 1: Values
Developer assigns Dist VID Correct VID Surface changes
version numbers 0.9.0 1.0.0 n/a
manually  bogus 0.9.2 1.1.0 extension
1.0.0 2.0.0 removal
or incorrect values
(natural human reasons) Dist VID Correct VID Surface changes
1.0.1 1.0.0 n/a
1.0.3 1.0.1 (none)
1.0.4 1.0.2 (none)
Analysis of an
OSGi project 1.2.0 2.0.0 modification
– 1.2.1 2.0.1 (none)
version stream 1.2.2 2.0.2 (none)
of two bundles 1.4.0 2.1.0 extension
1.4.1 2.2.0 extension
OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 4

5. Scenario 2: Consequences
Resolver believes
version id 
run-time failures
after clean bind
or update.
OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 5

6. Scenario 2: Consequences
Resolver believes
version id 
run-time failures
after clean bind
or update.
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7. Build-time solution:
Version generator
• Provably correct version identifiers
– (developing new bundle version, for update)
– compute changes from previous revision
– assign version numbers according to the
scheme semantics
• Implemented as ant task + supporting libraries
– works on .jar / .class, not on .java source
OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 7

8. Run-time solution:
Safe bundle update
• Enhanced update process
– check that declared compatible
is really compatible
– works on bundle .jar files
• Implemented as user-space
bundle
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9. Behind the scenes
• Based on type checking mechanism
• Reconstruct surface of bundle old, new
» actually, this is the hard work
• Check for subtype relation → difference
» the same thing as compiler does on assignment
• Results available for any level of bundle
structure (class, package, exports, bundle)
» use as flags for resolver, turn into version value
OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 9

10. Experiences & Summary
• Issues we ran into
– can’t check service interfaces etc
– can’t hook well into resolving process
– can’t rely on version id semantics
• API to access installed bundle’s JARs would help
• With finer and enforced version of “proper
imports” best practice, we can have type-safe
updates and bundle resolving
http://www.kiv.zcu.cz/research/groups/dss/
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