EvmConnection(5)						File Formats Manual						  EvmConnection(5)

NAME

       EvmConnection - connection to the EVM (Event Management) daemon

DESCRIPTION

       An EVM connection is the context through which data is passed to and from the EVM daemon.  A connection has the following attributes:

       o  Connection Type

       o  Response Mode

       o  Transport Type

       o  Callback, and associated Callback Argument

       o  Connection Context

       These attributes are described in the following sections.

       An  EVM	client is any program that processes events through the EVM daemon.  EVM supports three distinct types of client: posting clients,
       subscribing (listening) clients, and service clients.  Regardless of type, all clients connect to the EVM daemon in the same way.

   Connection Type
       The type of connection established determines the client type.  There are associated constants to be used when the connection is created.

       The client uses this connection to post events to the daemon for distribution.

       The client uses this connection to listen for events distributed by the daemon.

       The client uses this connection to request that the daemon provide a
		 service, such as retrieve events from a log.

		 A client may use all three types of connection, but must establish each connection separately.

   Response Mode
       The response mode associated with a connection determines the manner in which certain API functions will deal with the  daemon's  responses
       to request messages.  See the EvmConnCreate(3) reference page for full details of each mode.  The modes are:

       The API functions will return as soon as the request has been sent to
		 the daemon, and the caller will not receive the daemon's response.

       The API functions will send the request to the daemon, and wait until a
		 response has been received before returning to the caller.  The returned status code will reflect the response.

       The API functions will return as soon as the request has been sent to
		 the  daemon, and the caller must monitor the connection for a response.  When the response is received, the connection's callback
		 function will be invoked to handle it.

   Transport Type
       The transport type specifies the type of connection to be made to the daemon.  The only valid connection that can be made is:

       Connection is through a domain socket to a daemon running on the local host.

   Callback
       This attribute specifies the function you want to handle any incoming responses resulting from activity on the  connection.  Callbacks  are
       discussed in more detail in the EvmCallback(5) reference page.  This attribute is valid only when the Response Mode is

   Connection Context
       This attribute is a handle to a connection returned when a connection is created. You must pass this handle to all other functions you call
       which need to access the connection.

   Connection Monitoring
       Once you have established a connection, the API functions will take care of all communication activity with the daemon. However,  you  must
       make  sure that these functions get an opportunity to do their work when activity occurs. EVM provides several ways for you to do this. The
       method you choose depends on the model of your program.

       o  If your program is I/O driven, waiting for I/O to occur on one or more file descriptors, handling activity as it occurs and then return-
	  ing  to wait for more I/O, it probably spends most of its time in a call.  In this case, you should use to establish which file descrip-
	  tor the EVM connection is using, and then include that file descriptor in your read mask.  When you detect activity on  the  connection,
	  invoke to handle the activity.

       o  If  your  program  is driven purely by activity on a single EVM connection, you can let the API handle the I/O entirely by using to wait
	  for activity to occur on the connection.  When the function returns, dispatch the I/O using and then return to

       o  If your program is driven in some other way, and there are certain points (for example, at the end of some control loop)  at	which  you
	  want	to handle EVM activity, you can call to check for any outstanding activity.  If this function indicates that there is something to
	  do, you can call otherwise you can continue immediately with normal processing.

   Destroying a Connection
       When you are finished with the connection, use to disconnect from the daemon.  It is important to check the return status for  any  failure
       each time you call a connection function and destroy the connection if a failure occurred.  The file descriptor associated with the connec-
       tion remains open until you destroy the connection even if I/O errors have been detected on the connection.

SEE ALSO

   Functions
       select(2).

   Routines
       EvmConnControl(3), EvmConnCreate(3), EvmConnFdGet(3), EvmConnCheck(3), EvmConnWait(3), EvmConnDispatch(3), EvmConnDestroy(3).

   Event Management
       EVM(5).

   Event Callback
       EvmCallback(5).

   EVM Events
       EvmEvent(5).

																  EvmConnection(5)