UNIX Process Cryogenics?

shawarma asks: "Due to a recent power outage, I've had to shut down a server running a process that had been running for ages calculating something. The job it was doing would have been done in a few days, I think, but I had to shut it down before the UPS ran out of juice. This got me thinking: Why can't I freeze down the process and thaw it back up at a later time? It ought to be possible to take all the connected memory pages and save them in some way, preserve file handles and pointers, and everything. Maybe net-connections would die, but that's understandable. Has any work been done in this field? If not, shouldn't there be? I'd like to contribute in some way, but I think it's a bit over my head.." Laptops have been doing this in some form for years: most laptops, when they run out of power, or when told by the user will go into "suspend" mode which is similar to what the poster is describing, however outside of laptops, I haven't seen this done. Sleeping processes also do something similar, sending their memory pages into swap so other running processes can use the memory. What, if anything, is preventing someone from taking this a step further?

Comments

Build in persistence yourself.

[blair1q]

Any program that you intend to run for more than a day or two you should checkpoint its intermediate results to disk, even if this adds 100% to the run time.

--Blair

P.S. Alternatively, you could write a program to have the rebooted computer pull scrabble tiles from a bag structure and print them to the screen. You might at least get some clue as to whether it was asking the right question.

Hibernation comments are missing the point

[ry4an]

The comments to the effect of "it's called hibernation, and has done it for years" are missing the point. That hibernation is a BIOS supported dump to disk. It's a feature on most laptops and works with just about any OS -- it's worked on my Linux laptop for years.

I think the feature to be discussed is Operating System (not BIOS) level support of the hibernation of a single process. It'd be nice if I could do a:

kill -HIBERNATE `cat /var/longoperation.pid`

and have that program get frozen to disk. Then if I could resurrect just that process later it'd be a handy feature for the long running program that you want to postpone until after you've done whatever you needed to do in single user mode.

Re:Hibernation comments are missing the point

[Hrunting]

And if you have something like that, you open yourself up to a wealth of potential problems in the program. Take this simple perl script.

#!perl

use strict;

my $pid = $$;
print $pid


If you stop it between those two $pid commands, there's no guarantee that you're going to get the same pid value back. Programs would have to be specifically programmed to handle this sort of thing (there are other examples, this is just the most basic; network programs particularly would have problems).