6.1.4 Notes About Thread Safety

Aspell should be thread safe, when used properly, as long as the underlying compiler, C and C++ library is thread safe. Aspell objects, including the AspellSpeller class, should not be used by multiple threads unless they are protected by locks or it is only accessed by read-only methods. A method is read-only only if a const object is passed in. Many methods that seam to be read-only are not because they may store state information in the object.