Thread-safe versions of some of the tools

[Thilo Goetz]

Hi,

in a recent project, I was using SentenceDetectorME, TokenizerME and 
POSTaggerME. It turns out that none of those is thread safe. This is 
because the classification probabilities for the last tag() call (for 
example) are stored in a member variable and can be retrieved by a 
separate API call.

I'm planning to build thread safe versions for myself, and I'd be happy 
to contribute a patch if there is interest. This could be done as a 
conservative extension with an additional method such as tagReentrant, 
where the old API calls would continue to work as before and would still 
not be thread safe. Alternatively, one could remodel the API so that 
everything was thread safe, but that would break backwards compatibility.

Final question: if I do this for the classes mentioned above, are there 
other tools that should be made thread safe while we're at it?

Opinions?

--Thilo