Re: stupid question: how can I finish a program?

[Ole-Hjalmar Kristensen <oleh@vlinux.voxelvision.no>]

"Warren W. Gay VE3WWG" <ve3wwg@cogeco.ca> writes:

> Robert A Duff wrote:
> > Darren New <dnew@san.rr.com> writes:
> >>Robert A Duff wrote:
> >>>Darren New <dnew@san.rr.com> writes:
> >>>>Robert A Duff wrote:
> >>>>
> >>>>>If you're running under a proper operating system, then all resources
> >>>>>visible outside the program will be cleaned up when the program exits.
> >>>>
> >>>>This is true only in the most trivial sense. If I have a program that
> >>>>contacts a license manager (for example) and grabs the license, then aborts,
> >>>>I could be in trouble. That's why license managers check for that sort of
> >>>>failure.
> >>>
> >>>So if it's checked for, what's the problem?
> >>
> >>Well, it isn't the OS doing it.
> > OK, I admit, I was oversimplifying.
> > Still, if the OS allocates some physical memory to a process, and the
> > process dies, the OS ought to reclaim that memory.  If a license manager
> > allocates a license to a process, and the process dies, the license
> > manager ought to reclaim it.  ...
> 
> Even in "proper O/S" there are occaisions where cleanup is needed,
> but not automatically done by the O/S. Here are 3 examples of
> this, that can happen on [pick your] UNIX:
> 
>    - Allocated _SHARED_ memory
>    - Created message queues (IPC)
>    - Create semaphores
> 
> The reason these are not automatically cleaned up by the O/S is that
> sometimes you want them to persist beyond the creating process'
> lifetime (because they are shared by other processes).
> 

Certainly, it can cause a leak, but the leak does not get bigger when
you run the program again, because as you point out, you can aquire
the same resource again, and it's pretty trivial to check for the
existence of those *named* objects on startup. Contrast this with an
OS which leaks memory, does not close file handles, etc. On the next
run of the program, you will probably aquire a *new* chunk of memory
or another file handle, and so the garbage will build up over time.

<snip>