evmconnection.5 (2010 09)

EvmConnection(5) EvmConnection(5)

Connection Context

This attribute is a handle to a connection returned when a connection is created. You must pass this han-

dle 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.

• 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 returning to wait for more I/O, it probably spends most of its time in a

select() call. In this case, you should use

EvmConnFdGet() to establish which ﬁle descriptor the

EVM connection is using, and then include that ﬁle descriptor in your

select() read mask. When

you detect activity on the connection, invoke

EvmConnDispatch() to handle the activity.

• 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

EvmConnWait()

to wait for activity to occur on the connection. When the

function returns, dispatch the I/O using

EvmConnDispatch()

, and then return to

EvmConnWait().

• 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

EvmConnCheck()

check for any outstanding activity. If this function indicates that there is something to do, you can call

EvmConnDispatch()

; otherwise you can continue immediately with normal processing.

Destroying a Connection

When you are ﬁnished with the connection, use

EvmConnDestroy()

to disconnect from the daemon. It

is important to check the return status for any failure each time you call a connection function and des-

troy the connection if a failure occurred. The ﬁle descriptor associated with the connection remains open

until you destroy the connection even if I/O errors have been detected on the connection.