[DGD] Object upgrading

[Raymond Jennings]

On Tue, Jul 3, 2018 at 11:34 PM <bart at wotf.org> wrote:
>
> On Tue, 3 Jul 2018 17:44:40 -0700, Raymond Jennings wrote
>
> <snip>
>
> > > Second question, why suspend the system here, and not at the beginning of this
> > > entire process?
> >
> > The suspend is merely intended to protect the upgrade() call from
> > being preempted by regular activity.
>
> I understand WHY you suspend the system, that was not the question, the
> question was why do that just before starting the *DATA* upgrade part, and not
> before starting the compile.
>
> Unless you immediately follow with the upgrade after compile (in which case
> you will still have outdated code being active), you very likely want to have
> a call_out inbetween,

ah yes

I apologize if I neglected to mention that the upgrade() call takes
place in a separate task from the actual compilation.  Due to the
outdated code issue you cited, this is obviously something to look out
for.

This is how it works in kotaka

Task 1:

* compile
-- generating inheritance information, possibly compiling other
libraries along the way
-- the initd is asked for the patcher
* compiled!
-- ObjectD->compile(blah blah blah, inherited ...) tells the object
manager what was inherited,
-- Scour the inheritance tree and gather the patchers for all inheritables
-- tag all the clones with call_touch
* Suspend System
-- isolate the upgrade() cal
* call_out
-- We start a callout that arranges to call the object's upgrade() function

DGD internal:
* dump the old code, replace with the new code

Task 2:
* The callout in ObjectD from task 1 fires.
-- ObjectD calls object->upgrade()
-- Since the system is suspended, the upgrade() call will happen first
before anything else, unless multiple objects were compiled in which
case you will have more than one object doing an upgrade() call.
-- If the object has been flagged with call_touch and has patchers
listed, they will be called first

Task 3:
* SuspendD eventually notices that there's no more "priority tasks" to
run while suspended and automatically releases the system.

At any point after task 1 completes, any touched object will trigger
calls to the registered patchers listed by it and its inherits.

For full information I guess check kotaka's ObjectD and PatchD located
in ~System/sys


> and that also needs to be protected from other activity,
> hence my question: why not protect the entire process, so compile + everything
> related to upgrade until you can safely have other activities run again?
>
> Bart.
> --
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