Hi,

As Bill points, the library is thread/safe for search in 2.1.
All the memory allocated in SwishOpen, SwishSearch, etc 
should be freed in SwishClose. I do not know at this moment
if there is any remaining memory leak.

But this is not optimal because there are not any shared memory. 
In other words: If you have 2 threads and both of them opens the
same index, the header data of this index is twice in memory
although this data is identical.

cu
Jose