[Python-Dev] atexit missing an unregister method

[Guido van Rossum]

On 4/26/05, Nick Jacobson <nicksjacobson at hotmail.com> wrote:
> I was looking at the atexit module the other day; it seems like an elegant
> way to ensure that resources are cleaned up (that the garbage collector
> doesn't take care of).
> 
> But while you can mark functions to be called with the 'register' method,
> there's no 'unregister' method to remove them from the stack of functions to
> be called.  Nor is there any way to view this stack and e.g. call 'del' on a
> registered function.
> 
> This would be useful in the following scenario, in which x and y are
> resources that need to be cleaned up, even in the event of a program exit:
> 
> import atexit
> 
> def free_resource(resource):
>     ...
> 
> atexit.register(free_resource, x)
> atexit.register(free_resource, y)
> # do operations with x and y, potentially causing the program to exit
> ...
> # if nothing caused the program to unexpectedly quit, close the resources
> free_resource(x)
> free_resource(y)
> #unregister the functions, so that you don't try to free the resources
> twice!
> atexit.unregisterall()
> 
> Alternatively, it would be great if there were a way to view the stack of
> registered functions, and delete them from there.

Methinks that the resource cleanup routines ought to be written so as
to be reentrant. That shouldn't be too hard (you can always maintain a
global flag that means "already called").

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)