Are all RTI Connext API calls thread-safe?

Not all API calls are safe. 

In general, the get/ set_default_XXX_qos() and lookup_xxx() APIs are not thread-safe. The online HTML documentation for various API calls commonly include one or more MT Safety sections which describe any concerns about the use of individual calls in multi-threaded environments. 

Not all API call descriptions include MT Safety sections. For those that do not, all calls should be considered safe.