Re: Pausing and Resuming a Process

Suspending a thread is almost as bad an idea as suspending a process.
Suppose the thread
were in the middle of a storage allocation at the time you suspended it?
You have just
stopped EVERY thread from EVER using the allocator again!

The question about transferring a suspended thread to another machine is
even more
ill-considered than the problem of transferring a suspended process to
another system. I
cannot even being to imagine how it could be done, even under optimal
conditions.

This kind of dynamic handoff is an amazingly complex task. The code must
be carefully
designed to allow the transfer by having checkpoints that allow a
completely new program
to start up, compute the desired state from the saved checkpoint
information, and continue
running. I've done this on closely-coupled multiprocessors where we were
trying to deal
with processor failures, and it is incredibly difficult when you have
complete access to
the entire operating system source code. You can assume that for all
practical purposes,
the only way to accomplish this is to design the program so that it has
well-defined
checkpoints and can restart on some other machine from those checkpoints.
So essentially,
forget any concept of "transferring" either the program or a thread to
another machine. It
is not possible. What *is* possible is to transfer the necessary state to
allow a
completely separate execution of a program start up on another machine and
pick up where
the old computation left off. Using a transacted database for hold this
is a good
starting point, then it starts to get hard.
joe