grpc_wait_any - Waits for any session to end.
  grpc_error_t grpc_wait_any(grpc_sessionid_t *idPtr)
  grpc_sessionid_t *idPtrThe grpc_wait_any() function waits for any one of the currently executing sessions to end. When no executing sessions exist, the grpc_wait_any() function returns GRPC_NOERROR and sets GRPC_SESSIONID_VOID to the area pointed by idPtr.
This function is MT-unsafe.
If successful, GRPC_NO_ERROR is returned. In the case of an error, Error code is returned.
  GRPC_NOT_INITIALIZED  GRPC_SESSION_FAILED  GRPC_TIMEOUT_NP  GRPC_OTHER_ERROR_CODE