22nd June 2009, Zurich



 Bundle Updates with
Verified Compatibility
        Premek Brada
  University of West Bohemia
  ...
Agenda
•   Problems addressed
•   Version generator
•   Safe bundle update
•   How does it work
•   Experiences




OSGi D...
Problem addressed:
version id  implementation
      reality mismatch
• Scenarios                                         ...
Scenario 1: Values
  Developer assigns                               Dist VID         Correct VID         Surface changes
...
Scenario 2: Consequences
                                                                               Resolver believes
...
Scenario 2: Consequences
                                                                               Resolver believes
...
Build-time solution:
                   Version generator

• Provably correct version identifiers
      – (developing new ...
Run-time solution:
                  Safe bundle update
• Enhanced update process
      – check that declared compatible
 ...
Behind the scenes

• Based on type checking mechanism
• Reconstruct surface of bundle old, new
                          »...
Experiences & Summary
• Issues we ran into
      – can’t check service interfaces etc
      – can’t hook well into resolvi...
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Safe Bundle Updates

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Our recent research has resulted in a method that ensures safe OSGi bundle
updates and package bindings despite potentially errorneous meta-data, e.g.
package versions. It uses subtype checks and is implemented as a user-space
enhancement of the standard bundle update process. The method was successfully
applied in the Knopflerfish and Apache Felix frameworks; these implementations
also resulted in some general experiences with the OSGi framework which we want
to share.

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Safe Bundle Updates

  1. 1. 22nd June 2009, Zurich Bundle Updates with Verified Compatibility Premek Brada University of West Bohemia Pilsen, CZ
  2. 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. 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. 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. 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. 6. 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 6
  7. 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. 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 OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 8
  9. 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. 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/ OSGi DevCon 22.6.2009 Zurich Premek Brada - Bundle Updates with Verified Compatibility 10
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