/*D
   MPI_T_event_get_source - Returns the index of the source of the event instance

Synopsis:
.vb
int MPI_T_event_get_source(MPI_T_event_instance event_instance,
                           int *source_index)
.ve

Input Parameters:
. event_instance - event instance provided to the callback function (handle)

Output Parameters:
. source_index - index identifying the source (integer)

.N ThreadSafe

.N Errors
.N MPI_SUCCESS
.N MPI_T_ERR_INVALID
.N MPI_T_ERR_INVALID_HANDLE
.N MPI_T_ERR_NOT_INITIALIZED
.N MPI_ERR_OTHER

D*/

