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_r391276303
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/execution/librarycache/FlinkUserCodeClassLoaders.java
##########
@@ -82,4 +91,78 @@ 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.
+ *
+ * @param <T> the classloader type that also needs to be closeable.
+ */
+ private static class SafetyNetWrapperClassLoader<T extends ClassLoader
& Closeable> extends CloseableClassLoader
+ implements Closeable {
+ private static final Logger LOG =
LoggerFactory.getLogger(SafetyNetWrapperClassLoader.class);
+
+ private T inner;
+
+ SafetyNetWrapperClassLoader(T inner) {
+ super(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);
+ }
+
+ synchronized (getClassLoadingLock(name)) {
+ final Class<?> loadedClass =
findLoadedClass(name);
+ if (loadedClass != null) {
+ return resolveIfNeeded(resolve,
loadedClass);
+ }
+
+ return resolveIfNeeded(resolve,
inner.loadClass(name));
+ }
+ }
+
+ private Class<?> resolveIfNeeded(final boolean resolve, final
Class<?> loadedClass) {
Review comment:
Now that the safety net is a URLClassLoader we can just forward the call,
correct?
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