Tries to reopen the subreaders.
If one or more subreaders could be re-opened (i. e. subReader.reopen() returned a new instance != subReader), then a new MultiReader instance is returned, otherwise this instance is returned.

A re-opened instance might share one or more subreaders with the old instance. Index modification operations result in undefined behavior when performed before the old instance is closed. (see {@link IndexReader#Reopen()}).

If subreaders are shared, then the reference count of those readers is increased to ensure that the subreaders remain open until the last referring reader is closed.

Just like {@link #Reopen()}, except you can change the readOnly of the original reader. If the index is unchanged but readOnly is different then a new reader will be returned.

Expert: reopen this reader on a specific commit point. This always returns a readOnly reader. If the specified commit point matches what this reader is already on, and this reader is already readOnly, then this same instance is returned; if it is not already readOnly, a readOnly clone is returned.