Re: Orderly IOC shutdown?

[Andrew Johnson <anj@aps.anl.gov>]

Hi Michael,

Michael Abbott wrote:
> Is there any way to request the orderly shutdown of an IOC, waiting for 
> all IOC threads to terminate (I'm guessing not).

Probably not in the way you're looking for.  You can type 'exit' into 
the ioc shell which will stop the IOC, but you may not regard the 
resulting shutdown as 'orderly'.

> I have a lot of resources open which I would like to close cleanly: but 
> if IOC threads are still running then I have to synchronise with them to 
> ensure closed resources aren't used by calls from IOC threads.
>
> Am I better off just pulling the plug, leaving everything running and 
> relying on exit to do the right thing?
>
> I can (and do) shut my own threads down in an orderly fashion, but the 
> IOC threads seem to be out of reach.

The problem is that the IOC extensibility mechanisms (record, device and 
driver support etc.) were designed before the idea of porting to 
non-vxWorks systems came up, and the original concept for the vxWorks 
systems was that they boot up on power up, and then they run until they 
get turned off.  As a result there's nothing in the record support or 
device support interfaces to ask them to shut down nicely, and 
retro-fitting such an interface would be a major re-engineering effort 
(which we want to do anyway for other reasons too, but the results 
cannot be backwards-compatible and it's hard for APS to justify spending 
effort on such work).  We already know that the internal CA client that 
handles links has issues with IOC shutdown; I think there's 'string and 
sealing wax' in that code to try and be as tidy as possible, but it's 
not great.

You can use the epicsAtExit() facility to get callbacks when shutdown is 
occurring, but the current state of the other threads when this happens 
is not well-defined, meaning your I/O thread may be active at the time 
and there's nothing we can do about that.

> I'm running an EPICS 3.14 IOC as a Linux process, using iocsh(filename) 
> to load databases and get things rolling, and then running as a daemon 
> the rest of the time.

I hope you've heard of the GNU Screens program, which is a wonderful way 
of attaching to IOC consoles to provide simultaneous access to the 
console session, a history buffer and the ability to disconnect and 
reconnect at will.  We use this for both soft and hard IOCs here.

- Andrew
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