com.uber.tchannel.api.SubChannel not thread safe, not documented

[alshopov]

Class SubChannel keeps handlers in
private final Map<String, RequestHandler> requestHandlers = new HashMap<>();

most often calls to
public SubChannel register(String endpoint, RequestHandler requestHandler)
make structural changes to the HashMap which means that the SubChannel class is not thread safe - register(String endpoint, RequestHandler) must be called from a single thread (or change the underlying map implementation)