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  public class ComponentA
  {
    /// <summary>
    /// True if request for data has been send out
    /// </summary>
    private bool _hasSendRequests = false;
    
    /// <summary>
    /// List of items that needs to be exchanged in each time steup
    /// </summary>
    private List<IExchangeItem> ActiveItems;

    /// <summary>
    /// List of items in ActiveItems that have not yet been updated
    /// </summary>
    private List<IExchangeItem> PendingActiveItems;

    /// <summary>
    /// List of items that other linkable components have requested data for, 
    /// i.e., which is in the other linkable components PendingActiveItems list
    /// </summary>
    private List<IExchangeItem> IncomingRequests;


    /// <summary>
    /// Update the component, returns true if updated, false if not updated
    /// </summary>
    /// <param name="forceUpdate">Force the component to update always</param>
    public bool Update(bool forceUpdate)
    {
      // Check if we have already send out requests for active items for this timestep.
      if (!_hasSendRequests)
      {
        // We have not send requests, send a request for data for each active item
        foreach (IExchangeItem item in ActiveItems)
        {
          // Send request, see if data is already available
          // If data is not available, the other component registers this item in its list of IncomingRequests
          bool dataIsReady = SendRequestForData(item);
          if (dataIsReady)
          {
            // Data is ready, transfer data
            TransferDataFor(item);
          } 
          else 
          {
            // Data is not ready, put it in pending list
            PendingActiveItems.Add(item);
          }
        }
        _hasSendRequests = true;
      }

      // If this is a forced update, theget the best possible data for each pending active item
      if (forceUpdate)
      {
        foreach (IExchangeItem item in PendingActiveItems)
        {
          GetBestPossibleDataFor(item);
        }
        PendingActiveItems.Clear();
      }

      // If we have pending active items, we can not update the component
      if (PendingActiveItems.Count > 0)
        return (false);

      // No pending active items, we can update component to next timestep.
      DoUpdateComponent();

      // Check each incoming request, whether data is now available
      foreach (IExchangeItem item in IncomingRequests)
      {
        if (DataIsAvaiableFor(item))
        {
          // Data is now available for this item, send data to component. 
          // The other component must remove item from its PendingActiveItems
          TransferDataFor(item);
          IncomingRequests.Remove(item);
        }
      }
      return (true);
    }

  }