Here are some explanations concerning my latest commit on restructuring IndexReader/SegmentReader/MultiReader/FilterIndexReader
*) The reason for this restructuring was that directory locking in case of delete, undelete, and setNorm was a bit confused especially with MultiReader.
*) After some deep brain racking I decided to keep the old design and not to take Dougs proposal. All synchronization (directory locking in case of delete, undeleteAll, and setNorm) is now down in the abstract IndexReader class. However, not all IndexReaders necessarily do directory locking. Only those that are directory owners. This means that depending on the constructor used to construct an IndexReader (or one of its subclasses) it does directory locking or it does not. A SegmentReader that owns its directory (if it is the only segment in the directory) does directory locking, if the SegmentReader is part of a MultiReader that owns the directory, directory locking is done by the Multireader, and not by the individual SegmentReaders. This is the case for IndexReaders acquired from IndexReader.open(). There is also a public constructor for MultiReader, that takes an array of IndexReaders. In this case Multireader does no directory locking. The situation is similar for FilterIndexReader which also leaves locking to its base reader.
*) The API has not changed, however the bahavior of some API methods has changed slightly. The reason for this is that setNorm and undeletAll do change the index and therefore need a write lock on the directory. This was a so far undiscovered bug. The biggest differenc is that calling undeleteAll has only an effect on the the Readers. The changes are not written to the index before IndexReader.close is called. This is bahavior we are used to in case of delete.
*) Up till now IndexReader.close() always closed the directory, even if the IndexReader was acquired with IndexReader.open(Directory dir). This means that dir became unusable after opening and closing an Indexreader on it. I think this is not the behavior expected by users. I changed IndexReader so that IndexReader.close() no only closes its directory if IndexReader was opened with IndexReader.open(File) or Indexreader.open(String). If this change is accepted, we sould change IndexWriter in the same way.
*) This commit also changes some unit tests. TestIndexReader now fails with the old implementation since in the old implementation Multireader does no directory locking.
Christoph
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