Newsgroups: comp.parallel.pvm
From: Jonathan King <jking@cv.hp.com>
Subject: Re: adding hosts to a virtual machine
Organization: Hewlett-Packard Co.
Date: Tue, 16 Jul 1996 11:19:00 -0700
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Message-ID: <31EBDD14.6905@cv.hp.com>

C.M. Angus wrote:
> 
> Hi,
> 
> I have never actually used pvm and was wondering if it was possible to add a host
> to pvm to be included in an already running job. 

Yes.  You can either 1) add hosts from within your program with
pvm_addhosts() or 2) set up notification for PvmHostAdd, which will send
a message to your program with the tid of the new host.  You can then
query the configuration to determine host name, etc, if necessary.

> Or if a host fails for the job to continue. 

Yes.  This requires a bit more work, though, and is really only feasible
in a "master-worker" configuration, in which subtasks are delegated by a
central controller.  If the controller is smart enough to notice (again,
set up notification) the death of a worker, and remembers what that
worker was doing, another worker can be given the task instead.  This
strategy is mostly used when the subtasks are independent.  Once the
subtasks have to communicate with each other, this beocmes difficult.

Combine this with your first question, and you would have a VM capable
of dynamically taking advantage of hosts as they become available,
detecting worker failures, etc.  If your program is designed in a SPMD
(Single Program Multiple Data), in which the processes are peers, there
are some serious problems encountered.  Let me know if you want any
further information.

> Given that the running job is sophisticated enough to deal with these
> eventualities.

Both of the above solutions require adding significant sophistication to
your program.  Nothing too bad, though.

Good luck.
Jon

-- 
#######################################################
# Jonathan B. King        kingjo@research.cs.orst.edu #
# M.S. Student in C.S.    jking@cv.hp.com             #
#                                                     # 
#   My opinions are my own and do not represent the   #
#      views of either Hewlett Packard *or* OSU.      #
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