shameersss1 commented on code in PR #7828:
URL: https://github.com/apache/hadoop/pull/7828#discussion_r2235400661
##########
hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/nodelabels/NodeAttributesManagerImpl.java:
##########
@@ -741,7 +741,15 @@ public void refreshNodeAttributesToScheduler(NodeId
nodeId) {
if (host == null || host.attributes == null) {
return;
}
- newNodeToAttributesMap.put(hostName, host.attributes.keySet());
+
+ // Use read lock and create defensive copy since
+ // other threads might access host.attributes
+ readLock.lock();
+ try {
+ newNodeToAttributesMap.put(hostName, new
HashSet<>(host.attributes.keySet()));
Review Comment:
The issue is that.
1. The LOG statement which prints `newNodeToAttributesMap` tries to iterate
`host.attribute`
2. `host.attribute` gets modified by some other thread - leading to
concurrent modification exception.
There are two ways to solve this
1. As you said to readLock before LOG statement so that `host.attribute`
does not get modified during LOG statement
2. Create a defensive copy of `host.attribute` (under read lock because the
modification can happen at that time as well).
The rationale behind using option 2 to avoid logging inconsistency- Assume
that we readLock before LOG statement. Once the LOG statement is executed, some
other thread modifies the `host.attribute` this will lead to we logging
something and processing something else.
Creating a defensive copy make sure that we don't change value. i.e what is
LOGed gets processed as well.
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