Experimental Physics and Industrial Control System
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Marty Kraimer wrote:
So why did we invent epicsAtExit?
Does anyone remember?
I think it was to try and ensure that vxWorks IOCs shut down "nicely"
when rebooted with a Ctrl-X. The CA server gets a chance to close all
its sockets, thus the clients are immediately notified that the IOC is
going down. Without it, the clients don't find out until up to 35
seeconds later that the IOC is no longer there. Where an OS such as
Linux carries on running after a soft IOC shuts down it immediately
closes all of the CA server's TCP sockets as part of the process
tidy-up, so this problem doesn't appear on soft IOCs.
If a vxWorks IOC reboots up before a client even notices that it ever
went down, there could also be extra complications before it reconnects,
since the client's network stack just thinks that the TCP socket was
congested for a while but is still live; the network stack in the
restarted server will receive packets intended for the old socket and
will have to reject them. I don't know if there are any additional
timeouts that this might introduce.
I think there may also have been issues with shutdown on WIN32 systems,
the atExit() routines were being run after some DLLs had been unloaded
or something like that. I may be totally wrong about this though.
- Andrew
--
* * Matt Santos / / Leo McGarry * * For a Brighter America * *
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ANJ, 02 Feb 2012 |
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