In Condor PVM, Condor acts as the resource manager for the PVM daemon. Whenever your PVM program asks for nodes (machines), the request is re-mapped to Condor. Condor then finds a machine in the Condor pool via the usual mechanisms, and adds it to the PVM virtual machine. If a machine needs to leave the pool, your PVM program is notified of that as well via the normal PVM mechanisms.
There are several different parallel programming paradigms. One of the more common is the "master-worker" or "pool of tasks" arrangement. In a master-worker program model, one node acts as the controlling master for the parallel application and sends pieces work out to worker nodes. The worker node does some computation, and sends the result back to the master node. The master has a pool of work that needs to be done, and simply assigns the next piece of work out to the next worker that becomes available.
Condor PVM is designed to run PVM applications which follow the master-worker paradigm. Condor runs the master application on the machine where the job was submitted and will not preempt it. Workers are pulled in from the Condor pool as they become available.
Writing a PVM program that deals with Condor's opportunistic environment can be a tricky task. For that reason, we have been working on a project named MW. MW is a tool for making master-worker style applications in the Condor-PVM environment. For more information, see the MW home page.
We use a very slightly modified version of the standard PVM distribution. To learn more about these modifications, see our PVM modifications page.
There is more information on creating and submitting Condor-PVM jobs in the Condor-PVM section of the manual.