Headless snapshotting (was: Re: [squeak-dev] binary development (was:
3.11 and the trunk))
David Farber
dfarber at numenor.com
Wed Aug 26 17:58:11 UTC 2009
On Aug 26, 2009, at 9:53 AM, Eliot Miranda wrote:
> On Tue, Aug 25, 2009 at 3:54 PM, David Farber <dfarber at numenor.com>
> wrote:
>
> On Aug 25, 2009, at 2:28 PM, Eliot Miranda wrote:
>
> One of the things the headless support in VW allows which is quite
> nice is taking a shapshot which can then be restarted in a headless
> mode for debugging.
>
> Eliot - Was this VM or image-side support? Can you describe how it
> worked?
>
> All image side; no VM support. I can't describe it in detail as I
> never worked on it. But the basic idea is to have a switchable
> headless system in the image so that in deployment it runs headless
> and when an error occurs the error handler temporarily throws the
> switch, saves a snapshot and resets the switch. When the snapshot
> is restarted it will come up headful because the switch was thrown
> before the snapshot was taken. In the resuming snapshot the error
> handler then does something like an on: .. do: [:ex| self
> shapshotHeadful. ex pass] to allow the GUI to display the debugger.
I was hoping you were going to say VM side. :) Or, rather, I was
hoping that the context of your original message was initiating a
snapshot from outside a image (i.e. in response to a nightly cron job
to backup the image or a system shutdown event).
But, back to headless/headfull for a moment, doesn't Squeak do this
automatically already? When I run an image in headless mode, all
that happens is that no OS window is opened--but the Squeak UI
objects are all there (and running) in the image. Does VW do
something more, like destroy all the UI objects?
>
> Not quite the same, but very neat: The other day at Qwaq Craig
> Latta had a VM crash while running in a Parallels Linux VM under
> gdb. He was able to give me a copy of the VM snapshot at the point
> where gdb stopped the process, giving me the opportunity to debug
> the live app at my leisure. A cool idea.
>
> In other words, he was already running the Qwaq VM under gdb, so
> when the Qwaq VM crashed (and left him at a gdb prompt), he simply
> suspended the Parallels Linux VM and sent you a copy of the
> suspended Parallels Linux VM. Is that right?
>
> Right. Very nice, as the patient is on the table.
Yeah, full OS virtualization has some pretty cool use cases.
David
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