Re: EventLoop shutdown procedure..

On Mon, 2006-08-21 at 22:17 +1000, Robert Collins wrote:
> I'd like to make the shutdown procedure async as well - allowing things
> like swap log writing to use calls elsewhere in the codebase that are
> async - like the disk engines.

Makes sense.

> Heres my proposed api:
> - on EventLoop you can call addShutdownEvent(callback, callbackdata);
> - this builds up a vector of pending shutdown callbacks.
> - when the event loop detects its time to stop - i.e. because its had
> stop() called, or because its gone idle, it invokes the last registered
> callback. This has a signature like 'void SHUTDOWNEVENT(callback,
> callbackdata);'. The event loop will invoke it with the loop as the
> callback data - so when that routine completes, the loop will move onto
> the next shutdown event and so on.
> - When the last shutdown event returns, the loop will return to the
> caller of run().

Sounds reasonable. My first thinking was why not do this with a
broadcast message bus asking the subsystems to prepare for shutdown, but
this simple scheme is easier.
 
> This has a couple of ramifications:
> - we'll need to teach various layers like comms that there core can be
> shutdown *while* the event loop is still running - but this is
> conceptually quite easy IMO.

Yes.

> - we'll have a mismatch between some parts of reconfigure and this
> approach, for a but - but thats reasonably easy to deal with in the
> short term. Long term, if reconfigure becomes async itself it will be
> non problematic.

Agreed. Should not be a problem in itself. But getting the clean store
index management async while still allowing the comm loop to run will be
a bit of a challenge...

Regards
Henrik
Received on Wed Aug 23 2006 - 05:38:41 MDT