Python vs Java garbage collection?

[holger krekel]

Beni Cherniavsky wrote:
> On 2002-12-28, Stuart D. Gathman wrote:
> 
> > On Thu, 26 Dec 2002 15:28:35 -0500, Antonio Cuni wrote:
> >
> > > I'd like if python had a feature comparable to C++'s deterministic
> > > destructors; something like the following (invented syntax):
> > >
> > > def foo():
> > >   auto mymutex = acquire_mutex()
> > >   auto myfile = open(filename, 'w')
> > >   auto mysocket = open_socket()
> > >   do_stuff
> > >
> > > I presume it's not easy to assure that "auto" variables can be destroyed
> > > at the end of the function: e.g., what if objects bound to auto
> > > variables have refcount > 1 ?
> >
> I was lately thinking along similar lines.  For Jython and for any
> resource release, one must indicate explicitly when to destroy the object.
> Whatever syntax you use, you still define a predictable place where the
> object is destroyed.  No way around it.  So I don't think one should be
> troubled by remaining references to the object - if the programmer chose
> to end the object's life, he should realise that that's what he's doing.
> 
> > 1) This feature should not reclaim memory, only call __del__().If
> > references were still live, the effect would be the same as calling
> > __del__() on a live object.
> >
> > 2) __del__() would get called again when memory is actually reclaimed.
> > Therefore, your feature would be much safer if it called another special
> > function - say close() or dispose() at the end of the block.
> >
> I think this is a technical question: is it possible in CPython and Jython
> to mutate an existing object's class, to mark it as dead?  If yes, then a
> facility to explicitly force a __del__ if any (and fry the object so it
> can't be used any more) would be a solution for writing portable code:
> 
> x = acquire()
> try:
>     do_something(x)
> finally:
>     finalize(x)

why is this better than the traditional e.g.

lock.acquire()
try:
    do_critical_work()
finally:
    lock.release()

regards, 
    holger