// -*- IDL -*-

//=============================================================================
/**
 *  @file    CosLoadBalancing.idl
 *
 *  $Id$
 *
 *  @author Object Management Group
 */
//=============================================================================


#ifndef COSLOADBALANCING_IDL
#define COSLOADBALANCING_IDL

#include "PortableGroup.idl"
#include "orb.idl"

/**
 * @class CosLoadBalancing
 *
 * @brief This module defines the interfaces and data types used in
 * TAO's Load Balancing service.
 * @par
 * TAO's Load Balancer manages distribution of requests to replicas of
 * a given Object in an effort to ensure that the  applications/hosts
 * pointed to by the Object reference are as equally loaded as
 * possible, i.e. load balanced.
 * @par
 * The definition of 'load' is application specific, for example, some
 * applications may choose to load balance access to multiple
 * dedicated lines, or separate network interfaces, as well as more
 * traditional load balancing metrics, such as CPU or power load.
 */
module CosLoadBalancing
{
  typeprefix CosLoadBalancing "tao.lb";

  const IOP::ServiceId LOAD_MANAGED = 123456;  // @todo TBA by OMG

  typedef PortableGroup::Location Location;
  typedef PortableGroup::Properties Properties;

  // Types used for obtaining and/or reporting loads
  typedef unsigned long LoadId;

  // OMG defined LoadId constants.
  const LoadId LoadAverage = 0;
  const LoadId Disk = 1;
  const LoadId Memory = 2;
  const LoadId Network = 3;
  const LoadId RequestsPerSecond = 4;

  struct Load {
    LoadId id;
    float value;
  };
  typedef sequence<Load> LoadList;

  exception MonitorAlreadyPresent {};
  exception LocationNotFound {};
  exception LoadAlertNotFound {};
  exception LoadAlertAlreadyPresent {};
  exception LoadAlertNotAdded {};

  exception StrategyNotAdaptive {};

  interface LoadManager;

  interface Strategy
  {
    readonly attribute string name;

    Properties get_properties ();

    // Report loads at given location to the LoadManager.
    void push_loads (in PortableGroup::Location the_location,
                     in LoadList loads)
      raises (StrategyNotAdaptive);

    // Get loads, if any, at the given location.  Load balancing
    // strategies may use this method to query loads at specific
    // locations.  Returned loads are the effective loads computed by
    // the Strategy, as opposed to the raw loads maintained by the
    // LoadManager.
    LoadList get_loads (in LoadManager load_manager,
                        in PortableGroup::Location the_location)
      raises (LocationNotFound);

    // Return the next member from the given object group which will
    // requests will be forward to.
    Object next_member (in PortableGroup::ObjectGroup object_group,
                        in LoadManager load_manager)
      raises (PortableGroup::ObjectGroupNotFound,
              PortableGroup::MemberNotFound);

    // Ask the Strategy to analyze loads, and enable or disable alerts
    // at object group members residing at appropriate locations.
    oneway void analyze_loads (in PortableGroup::ObjectGroup object_group,
                               in LoadManager load_manager);

    // The loads at the given location should no longer be considered
    // when performing load analysis.
    // void location_removed (in PortableGroup::Location the_location)
    //   raises (LocationNotFound);
  };

  typedef Strategy CustomStrategy;

  // Property value for built-in load balancing Strategy.
  struct StrategyInfo
  {
    string name;
    Properties props;
  };

  interface LoadAlert
  {
    // Forward requests back to the load manager via the object group
    // reference.
    void enable_alert ();

    // Stop forwarding requests, and begin accepting them again.
    void disable_alert ();
  };

  // Interface that all load monitors must implement.
  interface LoadMonitor
  {
    // Retrieve the location at which the LoadMonitor resides.
    readonly attribute Location the_location;

    // Retrieve the current load at the location LoadMonitor resides.
    readonly attribute LoadList loads;
  };

  // Specification of LoadManager Interface
  interface LoadManager
    : PortableGroup::PropertyManager,
      PortableGroup::ObjectGroupManager,
      PortableGroup::GenericFactory
  {
    // For the PUSH load monitoring style.
    void push_loads (in PortableGroup::Location the_location,
                     in LoadList loads);

    // Return the raw loads at the given location, as opposed to the
    // potentially different effective loads returned by the
    // Strategy::get_loads() method.
    LoadList get_loads (in PortableGroup::Location the_location)
      raises (LocationNotFound);

    // Inform member at given location of load alert condition.
    void enable_alert (in PortableGroup::Location the_location)
      raises (LoadAlertNotFound);

    // Inform member at given location that load alert condition has
    // passed.
    void disable_alert (in PortableGroup::Location the_location)
      raises (LoadAlertNotFound);

    // Register a LoadAlert object for the member at the given
    // location.
    void register_load_alert (in PortableGroup::Location the_location,
                              in LoadAlert load_alert)
      raises (LoadAlertAlreadyPresent,
              LoadAlertNotAdded);

    // Retrieve the LoadAlert object for the member at the given
    // location.
    LoadAlert get_load_alert (in PortableGroup::Location the_location)
      raises (LoadAlertNotFound);

    // Remove (de-register) the LoadAlert object for the member at the
    // given location.
    void remove_load_alert (in PortableGroup::Location the_location)
      raises (LoadAlertNotFound);

    // The following load monitor methods are only used for the PULL
    // load monitoring style.

    // Register a LoadMonitor object for "pull" monitoring of the
    // given location.
    void register_load_monitor (in PortableGroup::Location the_location,
                                in LoadMonitor load_monitor)
      raises (MonitorAlreadyPresent);

    // Retrieve the LoadMonitor object for the given location.
    LoadMonitor get_load_monitor (in PortableGroup::Location the_location)
      raises (LocationNotFound);

    // Remove (de-register) the LoadMonitor object for the given
    // location.
    void remove_load_monitor (in PortableGroup::Location the_location)
      raises (LocationNotFound);

  };

};

#endif  /* COSLOADBALANCING_IDL */