Re: Session ending shutdown problem
- From: Joseph M. Newcomer <newcomer@xxxxxxxxxxxx>
- Date: Thu, 19 Feb 2009 13:18:54 -0500
I think the timeout is 20 seconds.
THere is a fairly complex solution, which involves using WMI as a communication mechanism.
But it imposes a significant burden on you to figure out how to use it, and it means your
IT people would have to know how to use an app that shut down your apps, so it may not be
viable as a solution.
One problem is the fundamental architectural decisions you have made. If you have a
massively long shutdown time, you will have to rethink what it means to "shut down". For
example, if it is taking too long to communicate with the databases, one simplistic
approach is to instantly create a "transaction" file that captures all pending requests,
and start routing everything to it instead of the databases. You would immediately shut
down the databases (preferrably out of a separate thread) and any data that arrived after
this process starts gets appended to the transaction file instead. This would typically
be a faster operation. The way you append is Open/Append/Close each time, so that you
have minimum exposure to an abrupt shutdown.n When the program restarts, you then "spool
out" any pending transactions and send them to the databases as appropriate. So the idea
is to immediately upon shutdown notification replace the heavyweight database transactions
with lightweight file transactions that are intended to be robust-under-shutdown. When
you complete the transactions you have saved, you can delete the transaction file (and you
end up having to deal with what happens if another shutdown comes in during the
transaction despooling). I would remove ANYTHING that was in the destructor of the
CWinApp class; that is far, far too late to be doing anything important. Destructors
should be used for local cleanup only; anything dealing with databases needs to be handled
long before that (it also suggests that you have a lot of "global" variables in your
CWinApp class, which is really not a good decision)
joe
On Wed, 18 Feb 2009 17:52:50 -0700, r norman <r_s_norman@xxxxxxxxxxxx> wrote:
I have a number of MFC MDI applications that run constantly andJoseph M. Newcomer [MVP]
unattended, essentially as embedded systems, to monitor and control a
variety of system hardware. They do have a user interface to help
manage the system but every user action requires a password-controlled
logon. A password is also needed to exit the program by whatever
normal means.
The problem is that IT personnel do remote maintenance on all the
systems including these and they can't shut down the program easily --
a password entry box pops up on the remote system but nobody is there
to enter one! So they just shut down Windows and my application loses
data.
Of course I can detect the QueryEndSession and EndSession messages.
The problem (I think) is that my shutdown takes too long -- there are
perhaps a dozen socket connections and several database tables that
have to be closed cleanly and many score data structures with
internal states that all need serialization so the system can be
restored properly at startup.
Here are some details: If I initiate a program close at
QueryEndSession and return FALSE to halt further system shutdown,
everything works fine. If I initiate a program close at either
QueryEndSession or EndSession but allow the system to actually
shutdown, then my program is aborted before all the data can be saved.
Most of my system saving is done during ExitInstance but some is also
done at the d'tor of my CWinApp derived class.
My current workaround is to shut down on QueryEndSession, returning
FALSE and force the IT people to perform a second shutdown.
Alternatively I can provide them with a separate program that tells my
application to close cleanly, but there is no promise that I can get
all the IT staff to actually do that. I would like behave nicely,
though and shut down cleanly on a single EndSession.
Is this a known issue? Am I simply doing something wrong? I confess
(if it is not already obvious) that I really don't understand how
EndSession works. Actually, I don't understand how MFC shutdown
works, for example why posting WM_QUIT does not properly close the
program whereas posting WM_CLOSE does. It is exactly OnClose where I
require the password. Is there some way I can force EndSession
processing to wait until my program is completely done?
email: newcomer@xxxxxxxxxxxx
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm
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