Spinoff from here:
If you open an IndexSearcher/Reader, passing in String or File, then
closeDirectory is set to true in the reader.
If the index has a single segment, then SegmentReader.get is used to
open the index. If an IOException is hit in there, the SegmentReader
closes itself and then closes the directory since closeDirectory is
The problem is, the retry logic in SegmentInfos (to look for another
segments_N to try) kicks in and hits an AlreadyClosedException,
masking the original root cause.
Workaround is to separately get the Directory using
FSDirectory.getDirectory, and then instantiate IndexSearcher/Reader
This manifests as masking the root cause of a corrupted single-segment
index with a confusing AlreadyClosedException. You could also hit
the false exception if the writer was in the process of committing
(ie, a retry was really needed) or if there is some transient IO
problem opening the index (eg too many open files).