[Python-Dev] atexit missing an unregister method
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. --Nick Jacobson _ Dont just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/ ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] atexit missing an unregister method
On 4/26/05, Nick Jacobson [EMAIL PROTECTED] 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/) ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
RE: [Python-Dev] atexit missing an unregister method
[Nick Jacobson] 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. . . . Alternatively, it would be great if there were a way to view the stack of registered functions, and delete them from there. Please file a feature request on SourceForge. Will mull it over for a while. My first impression is that try/finally is a better tool for the scenario you outlined. The issue with unregister() is that the order of clean-up calls is potentially significant. If the same function is listed more than once, there would be no clear-cut way to know which should be removed when unregister() is called. Likewise, I suspect that exposing the stack will create more pitfalls and risks than it could provide in benefits. Dealing with a stack of functions is likely to be clumsy at best. Raymond Hettinger ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] atexit missing an unregister method
Nick Jacobson wrote: 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. You can always build your own mechanism for managing cleanup functions however you want, and register a single atexit() hander to invoke it. I don't think there's any need to mess with the way atexit() currently works. -- Greg Ewing, Computer Science Dept, +--+ University of Canterbury, | A citizen of NewZealandCorp, a | Christchurch, New Zealand | wholly-owned subsidiary of USA Inc. | [EMAIL PROTECTED] +--+ ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
