Major Description
This took some time to track down ... it's the root cause of the RangeTree failures that steve_rowe found at https://issues.apache.org/jira/browse/LUCENE-6697?focusedCommentId=14696999&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14696999
The problem happens when one thread is using the original IndexInput (RAMInputStream) from a RAMDirectory, but other threads are also cloning that IndexInput at the same time.