AHeise commented on a change in pull request #11303: [FLINK-16245] Decoupling
user classloader from context classloader.
URL: https://github.com/apache/flink/pull/11303#discussion_r393237279
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/execution/librarycache/FlinkUserCodeClassLoaders.java
##########
@@ -82,4 +89,61 @@ public static ResolveOrder fromString(String resolveOrder) {
super(urls, parent);
}
}
+
+ /**
+ * Ensures that holding a reference on the context class loader
outliving the scope of user code does not prevent
+ * the user classloader to be garbage collected (FLINK-16245).
+ *
+ * <p>This classloader delegates to the actual user classloader. Upon
{@link #close()}, the delegate is nulled
+ * and can be garbage collected. Additional class resolution will be
resolved solely through the bootstrap
+ * classloader and most likely result in ClassNotFound exceptions.
+ */
+ private static class SafetyNetWrapperClassLoader extends URLClassLoader
+ implements Closeable {
+ private static final Logger LOG =
LoggerFactory.getLogger(SafetyNetWrapperClassLoader.class);
+
+ private FlinkUserCodeClassLoader inner;
+
+ SafetyNetWrapperClassLoader(FlinkUserCodeClassLoader inner) {
+ super(new URL[0], null);
+ this.inner = inner;
+ }
+
+ @Override
+ public void close() {
+ if (inner != null) {
+ try {
+ inner.close();
+ } catch (IOException e) {
+ LOG.warn("Could not close user
classloader", e);
+ }
+ }
+ inner = null;
+ }
+
+ @Override
+ protected Class<?> loadClass(String name, boolean resolve)
throws ClassNotFoundException {
+ if (inner == null) {
+ return super.loadClass(name, resolve);
Review comment:
I understand where you are coming from, but this will effectively make any
job with leaked context classloader fail eventually, even if just basic Java
stuff needs to be loaded.
If we want to go that route, we should think twice what to throw. An
`IllegalStateException` would be the correct one, but does it fit in all cases?
We could also throw a `ClassNotFoundException` to not change the behavior too
much and provide a good description, but that may trigger some unwanted
fallback logic in user libraries.
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