During startup, the PMDF Job Controller reads a configuration file that specifies parameters, queues, and channel processing information. This configuration information is specified in /pmdf/table/job_controller.cnf (UNIX) or C:\pmdf\table\job_controller.cnf (NT). The format of the configuration file is described in Section 10.3. There is also a site-specific configuration file job_controller.cnf_site.

If you want to modify the default queue configuration or add additional queues, you can do so by modifying the job controller configuration, and then stopping and restarting the Job Controller with the command:

pmdf restart job_controller

On NT, you can also restart the Job Controller from the Services screen under the Control Panel.

A new Job Controller process is created, using the new configuration, and receives subsequent requests. The old Job Controller process continues to execute any requests it has queued until they are all finished, and then it exits. Note that you can stop the Job Controller at any time using the command:

pmdf shutdown job_controller

which gracefully shuts down the Job Controller, allowing any queued requests to finish. On NT, you can also shut down the Job Controller from the Services screen under the Control Panel.

The DEFAULT queue in the Job Controller configuration file, by default the only queue, is used for any requests which do not explicitly specify the name of a queue. Processing requests for specific channels can be directed to a specified queue by using the queue option followed by the name of the queue. This name must match the name of a defined queue. If the Job Controller does not recognize the requested queue name, the DEFAULT queue is used.

Typically, you would add additional queues to the Job Controller configuration if you wanted to separate processing of some channels from that of other channels. For example, you might need to prevent messages sent to a relatively slow channel from blocking processing of messages sent to other channels.

You might also choose to use queues with different characteristics. For example, you might need to control the number of simultaneous requests that some channels are allowed to process. You can do this by creating a new queue with the desired job limit and then use the queue option to direct those channels to the new, more appropriate queue.

In addition to the definition of queues, the Job Controller configuration file also contains a table of PMDF channels and the commands that the Job Controller is to use to process requests for each channel. There are two types of requests, termed master and slave. Typically, a channel's master program is invoked when there is a message stored in a PMDF message queue for the channel. The master program dequeues the message and deivers it. A slave program is invoked to poll a channel and pick up any messsages inbound on that channel. While nearly all PMDF channels have a master program, many do not need a slave program. For example, a channel which handles SMTP over TCP/IP doesn't use a slave program because a network service, the SMTP server, receives incoming SMTP messages upon request by any SMTP client. The SMTP channel's master program is PMDF's SMTP client.