snehashisp commented on code in PR #18403:
URL: https://github.com/apache/kafka/pull/18403#discussion_r1908232685
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connect/runtime/src/main/java/org/apache/kafka/connect/runtime/isolation/ReflectionScanner.java:
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@@ -76,8 +78,21 @@ private static <T> String versionFor(Class<? extends T>
pluginKlass) throws Refl
@Override
protected PluginScanResult scanPlugins(PluginSource source) {
+ // By default, java and classgraph uses parent first classloading,
hence if a plugin is loaded by the classpath
+ // loader, and then by an isolated plugin loader, the default
precedence will always load the classpath version.
+ // This breaks isolation and hence connect uses isolated plugin
loaders, which are child first classloaders.
+ // Therefore, we override the classloader order to be child first, so
that the isolated plugin loader is used first.
+ // In addition, we need to explicitly specify the full classloader
order, as classgraph only scans the classes available
+ // in the classloaders and not the entire parent chain. Due to this
reason if a plugin is extending a class present
+ // in classpath/application it will not be able to find the parent
class unless we explicitly specify the classloader order.
+ List<ClassLoader> classLoaderOrder = new ArrayList<>();
+ ClassLoader cl = source.loader();
+ while (cl != null) {
+ classLoaderOrder.add(cl);
+ cl = cl.getParent();
+ }
Review Comment:
> So the order of the specified classloaders does change the classloading
order of the plugins, even though it doesn't change the scanning behavior.
Yes, that's why with `addClassLoader` which uses
`environmentClassLoaderDelegationOrder` in `ClassGraphClassLoader` always finds
the files in the classpath loader (AppClassLoader) before PluginClassLoder has
a chance to kick in.
Also, yeah maybe with a special handler for PluginClassLoader we can avoid
having to pass the entire class loader chain in the reverse order.
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