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[stp-dev] Fwd: [orbit-dev] Problems with the Export-Package "uses" directive
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This just came in on the orbit list from Tom Watson. Let's
check to see if we are using the uses: directive.
cheers
-oh
Hello all.
I am sending this note to inform the community that the Export-
Package "uses" directive can critically effect the performance of
the Equinox OSGi package resolver when a system contains a large
set of bundles (1000s) and there are multiple exporters of the same
package name. See https://bugs.eclipse.org/bugs/show_bug.cgi?id=216934
Unfortunately this means that as a community we should *not*
include any bundles that declare the Export-Package "uses"
directive in the Ganymede release. Here is an example of a bundle
manifest file (META-INF/MANIFEST.MF) with an Export-Package
statement that contains a "uses" directive
Bundle-SymbolicName: foo
Export-Package: com.foo; uses:="com.bar"
More details:
The Export-Package "uses" directive in OSGi is used by the
Framework to ensure class space consistencies when multiple
exporters of a package exist in the Framework. In the above example
there may be multiple exporters of the "com.bar" package in the
Framework. This Export-Package statement is informing the Framework
that in order for a bundle to get wired to the "com.foo" package
exported by the "foo" bundle then the importing (or requiring)
bundle must be wired to the same exporter of "com.bar" as the foo
bundle is.
This is essential when dealing with multiple exporters of the same
package. Unfortunately the problem of resolving the state with
"uses" clauses appears to be an NP-hard problem to solve. Please
see bug https://bugs.eclipse.org/bugs/show_bug.cgi?id=216934 if you
have ideas of how to solve such a problem.
Thanks and sorry for the inconvenience.
Tom
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