zentol 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_r394169770
##########
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 think we can be sure a class loaded from the user-jar can only leak
something through a separate thread.
But we aren't sure at all what libraries in /lib are doing.
JCL for example does keep references around (and even
[documents](https://cwiki.apache.org/confluence/display/COMMONS/Logging+UndeployMemoryLeak)
that), but I don't see a way to handle this from our end.
My conclusions would be that users should stop throwing dependencies into
/lib and create fatter user-jars instead.
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