External Function (a_v4_extfn_proc)

The server uses the a_v4_extfn_proc structure to call into the various entry points in the UDF. The server passes an instance of a_v4_extfn_proc_context to each of the functions.

• _start_extfn
  Use the _start_extfn v4 API method as an optional pointer to an initializer function, for which the only argument is a pointer to a_v4_extfn_proc_context structure.
• _finish_extfn
  Use the _finish_extfn v4 API method as an optional pointer to a shutdown function, for which the only argument is a pointer to a_v4_extfn_proc_context.
• _evaluate_extfn
  Use the _evaluate_extfn v4 API method as a required function pointer that is called for each invocation of the function on a new set of argument values.
• _describe_extfn
  _describe_extfn is called at the beginning of each state to allow the server to get and set logical properties. The UDF can do this by using the six describe methods (describe_parameter_get, describe_parameter_set, describe_column_get, describe_column_set, describe_udf_get, and describe_udf_set) in the a_v4_proc_context object.
• _enter_state_extfn
  The UDF can implement the _enter_state_extfn v4 API method as an optional entry point to be notified whenever the UDF enters a new state.
• _leave_state_extfn
  The _leave_state_extfn v4 API method is an optional entry point the UDF can implement to receive a notification when the UDF moves out of a query processing state.