Opening and Closing a Port
The language monitor uses the OpenPortEx function to create and return a port handle. Typically, a language monitor calls its associated port monitor's OpenPort function, and the language monitor just returns the handle obtained from the port monitor's OpenPort.
If a language monitor is not associated with a port, the spooler calls the port monitor's OpenPort function directly.
The spooler does not allow more than one path to a port to be enabled at one time. Thus, after it has called OpenPortEx (or OpenPort) in a particular monitor, it does not attempt to open the same port again before closing it.
After a port has been opened, the spooler can call additional functions to print a job, as described in Printing a Print Job, using the port handle as an input argument. A monitor should be written so that, after a port has been opened, the spooler can send multiple print jobs before closing the port.
The spooler closes a port if a job must be sent through a different language monitor, if no print queues are associated with a port, or when the system shuts down. To close a port, the spooler calls a language monitor's ClosePort function. The function invalidates the handle that was created when the port was opened. A language monitor typically calls the ClosePort function defined by its associated port monitor.
If a language monitor is not associated with a port, the spooler calls the port monitor's ClosePort function directly.