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https://issues.apache.org/jira/browse/HADOOP-18781?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17738275#comment-17738275
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ASF GitHub Bot commented on HADOOP-18781:
-----------------------------------------
steveloughran commented on code in PR #5780:
URL: https://github.com/apache/hadoop/pull/5780#discussion_r1245676090
##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/BackReference.java:
##########
@@ -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
> ABFS Output stream thread pools getting shutdown during GC.
> -----------------------------------------------------------
>
> Key: HADOOP-18781
> URL: https://issues.apache.org/jira/browse/HADOOP-18781
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs/azure
> Reporter: Mehakmeet Singh
> Assignee: Mehakmeet Singh
> Priority: Major
> Labels: pull-request-available
>
> Applications using AzureBlobFileSystem to create the AbfsOutputStream can use
> the AbfsOutputStream for the purpose of writing, however, the OutputStream
> doesn't hold any reference to the fs instance that created it, which can make
> the FS instance eligible for GC, when this occurs, AzureblobFileSystem's
> `finalize()` method gets called which in turn closes the FS, and in turn call
> the close for AzureBlobFileSystemStore, which uses the same Threadpool that
> is used by the AbfsOutputStream. This leads to the closing of the thread pool
> while the writing is happening in the background and leads to hanging while
> writing.
>
> *Solution:*
> Pass a backreference of AzureBlobFileSystem into AzureBlobFileSystemStore and
> AbfsOutputStream as well.
>
> Same should be done for AbfsInputStream as well.
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