Need to detail the various ways the Tuscany runtime loads classes and the issues involved. Here are some notes to kick of this document

Classloading Objectives

The runtime must work in both OSGi and non-OSGI environments. I.e. we can't rely on the OSGi service registry for extensibility
The runtime must not be genberally environment specific. I.e. no buddy classloading
...

General Patterns

Extension loading - JSE

tuscany-extensibility
Tuscany finds extensions by looking for META-INF/services files on the classpath.

Extension loading - OSGi

tuscany-extensibility-equinox
It's a bit more complicated here. The extensibility-equinox bundle is given the entire OSGi context at start up and from there is looks in all of the loaded bundles looking for META-INF/services files. It caches them against the bundle in which they are found.

The tuscany-extensibility-equinox bundle also has a dynamic import

DynamicImport-Package: org.apache.tuscany.sca.extensibility.equinox,
javax.transaction;version="1.1",
javax.transaction.xa;version="1.1",

Which allows it to generally load any classes in the runtime

Split Packages

Third-party libraries - JSE

TBD

Third-party libraries - OSGI

Third-party libraries often rely on TCCL to load implementation classes in an extensible way. For example, the SDO API loads the HelperContext implementation in this way. In an OSGi environment there will not be a static dependency between the api bundle and the impl bundle so we need to fake it. Typically we do this by setting up the TCCL appropriately before the library us called.

See ClassLoaderContext which help us to set up a multi-classloader configurations.

Typically in OSGi one of the classloaders we pass in here will be the extensibiliy-equinox bundle classloader (the ServiceDiscoverer) as this bundles has a dynamic import which allows it to load any class in the runtime.

Tuscany Node API - JSE

TBD

Tuscany Node API - OSGi

There are a small number of Tuscany Jars you need to use in the app launcher in the OSGi environment

tuscany-sca-api
tuscany-node-api
tuscany-node-launcher-equinox

The node API has to load the node implementation and has a dynamic import in its manifest

DynamicImport-Package: org.apache.tuscany.sca.node.impl,org.apache.tuscany.sca.extensibility

SCA Client API - JSE

Factory finder impl is injected into the API class by the implementation

SCA Client API - OSGi

NodeFactory maintains a NodeProxy inner class that supports cross-classloader calls. The calling client api will have been loaded by the app classloader but the underlying node will have been loaded by a bundle classloader. We need to bridge that gap.