[pywin32-bugs] [ pywin32-Feature Requests-739624 ] Implement SetConsoleCtrlHandler

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Feature Requests item #739624, was opened at 2003-05-19 10:38
Message generated for change (Comment added) made by mhammond
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Category: None
Group: None
Status: Open
Priority: 5
Submitted By: Mark Hammond (mhammond)
Assigned to: Nobody/Anonymous (nobody)
Summary: Implement SetConsoleCtrlHandler 

Initial Comment:
Includes a patch and discussion.

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>Comment By: Mark Hammond (mhammond)
Date: 2003-05-19 10:39

Message:
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user_id=14198

we talked about SetConsoleCtrlHandler a while ago.

>Sorry for the delay, but yes, that sounds like a reasonable 
> approach.  The only problem is with the "last-registered, 
> first-called" approach, meaning second calls to your 
> extensions function would not have the same effect as a
> second call to the real SetConsoleCtrlHandler - but yeah, 
> I see no reasonable solution worth the effort.
>
>The GIL management will not be trivial, and may require 
> you to get - err - creative :)

The GIL wasn't too hard in the end - the handler is called
in the context 
of a new thread, and there is precedent for that in the
source :)

I have attached a simplistic version of a
SetConsoleCtrlHandler. It allows 
to set *one* handler function and doesn't implement the list
I originally 
had in mind.

The code works works, but its behaviour is far from the
behaviour of 
SetConsoleCtrlHandler in a C program.

This is probably due to the signal handling of Python
itself, and I can't 
see what can be done about it.

The current code is useful to me, and it could be improved
to handle 
multiple handlers properly (by installing different C
handlers, thereby 
preserving the order), but it would be rather hard to
document the 
behaviour, since it clashes with the Python internal signal
handling.

For example, take:

import cch # this is the console controle handler module
import time

def handler(type):
     print type
     return False

cch.SetConsoleCtrlHandler(handler, True)

time.sleep(60)

If you execute this, and hit Ctrl-C before the 60 seconds
are up, the 
handler will dutifully print 0, but the process won't be
killed - because 
time.sleep() cannot be killed in Python.

If you do a sys.exit() in the handler function, it will also
not terminate 
the process, since sys.exit() only works from the main thread.

Basically, I have no clue how the Python
SetConsoleCtrlHandler should be 
documented. It would need a link to description of standard
Python signal 
handling to be generally useful, but I am not aware of any
such documentation.



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