steveloughran commented on code in PR #5780:
URL: https://github.com/apache/hadoop/pull/5780#discussion_r1245676090
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hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/BackReference.java:
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@@ -0,0 +1,37 @@
+package org.apache.hadoop.fs.impl;
+
+import javax.annotation.Nullable;
+
+import org.apache.hadoop.classification.VisibleForTesting;
+
+/**
+ * Holds reference to an object to be attached to a stream or store to avoid
+ * the reference being lost to GC.
+ */
+public class BackReference {
+ private final Object reference;
+
+ public BackReference(@Nullable Object reference) {
+ this.reference = reference;
+ }
+
+ /**
+ * is the reference null?
+ * @return true if the ref. is null, else false.
+ */
+ public boolean isNull() {
+ return reference == null;
+ }
+
+ @VisibleForTesting
+ public Object getReference() {
Review Comment:
ideally i'd want this to be completely opaque: you can pass in a back
reference but never see what it was to.
I know this means the tests have to get less sophisticated, but we can still
assert that the reference is non-null and rely on code review to make sure it
is the right type
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