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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