class CAVERNdb_sharedState_c : public CAVERNmisc_observer_c

Encapsulates a shared state to be maintained between multiple users

Inheritance:

Public Methods

CAVERNdb_sharedState_c ()
Class constructor.
CAVERNdb_sharedState_c ( CAVERNdb_client_c *dbclient, char *path, char *key )
Class constructor
virtual ~CAVERNdb_sharedState_c ()
Class destructor.
inline bool isSharingEnabled ()
Returns the sharing status of this state.
inline void enableSharing ()
Sets the sharing enabled flag to TRUE.
inline void disableSharing ()
Sets the sharing enabled flag to FALSE.
int refresh ()
Requests a refresh of the data

Protected Fields

CAVERNnet_datapack_c _packer
data packing object
CAVERNdb_client_c* _dbclient
pointer to a database client which will make the transmissions
bool _sharingEnabled
flag for indicating whether or not sharing is enabled
char* _path
path name in the database for storing this state
char* _key
key name in the database for storing this state

Protected Methods

virtual int packAndSendState ()
Packs the object state and transmits it to the database server
virtual int unpackState ( char *data )
Unpacks the object state from the data buffer

Inherited from CAVERNmisc_observer_c:

Public Methods

virtual void update(CAVERNmisc_subject_c * )

Documentation

Encapsulates a shared state to be maintained between multiple users. This class provides a base abstract class from which to derives shared state information which multiple users encounter. This state needs to be managed by a database client in order to maintain consistency, but the client itself is external to the scope of the state. This state is associated with a particular path and key that should not change throughout the life of the state.

Updates are handled through the user of the subject-observer pattern. The shared state observes the client, so when new data arrives, it will unpack the state information provided that sharing is enabled. Sharing is initially disabled for initialization purposes, but can be enabled and disabled later as required.

Subclasses of the shared state have the responsiblity of handling the format of the state for transmission. The state will need to be packed using the packer instance and then sent through the database client. This process is handled by each client because the packing will vary, and the send is dependent upon the size of the packed data. Unpacking state information, however, can be done with just the data itself.

CAVERNdb_sharedState_c( CAVERNdb_client_c *dbclient, char *path, char *key )
Class constructor. Creating an instance of a shared state requires a reference to a database client which already exists. The state will be registered with the client as an observer. Additionally, path and key names are stored within the state for tranmitting and receiving state updates.
Parameters:
dbclient - pointer to an instantiated database client
path - path string to associate with this state
key - key string to associate with this state

int refresh()
Requests a refresh of the data. This method requests the remote state information from the database. It may be useful to call after creating the state.

virtual int packAndSendState()
Packs the object state and transmits it to the database server. The state information must be packed into a data buffer and sent to the database server. The responsibility of packing the state AND sending are placed within this method, so subclasses must put the state information into the database themselves.
Returns:
result Result of the attempt to send the state to the server

virtual int unpackState( char *data )
Unpacks the object state from the data buffer. The state receives a data buffer from the client when an update has occurred, but the state information must be unpacked from that buffer. This virtual method must be implemented in any derived subclass to extract the appropriate information from the data buffer received from the client. It is highly advisable to check the data's path, key, and size for security.
Parameters:
data - character data buffer received from the server

This class has no child classes.
Author:
cavern@evl.uic.edu
Version:
03/26/2000

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