Michael Foord wrote:
On 06/05/2011 18:26, Mark Shannon wrote:
Michael Foord wrote:
On 06/05/2011 17:51, Stefan Behnel wrote:
Mark Shannon, 06.05.2011 18:33:
s...@pobox.com wrote:
Antoine> Since we're sharing links, here's Matt Mackall's take:
Antoine>
http://www.selenic.com/pipermail/mercurial-devel/2011-May/031055.html
From that note:
1: You can't have meaningful destructors, because when destruction
happens is undefined. And going-out-of-scope destructors are
extremely
useful. Python is already a rather broken in this regard, so feel
free
to ignore this point.
Given the presence of cyclic data I don't see how reference
counting or
garbage collection win. Ignoring the fact that in a pure reference
counted
system you won't even consider cycles for reclmation, would both
RC and GC
have to punt because they can't tell which object's destructor to
call
first?
It doesn't matter which is called first.
May I quote you on that one the next time my software crashes?
Arbitrarily breaking cycles *could* cause a problem if a destructor
attempts to access an already collected object. Not breaking cycles
*definitely* leaks memory and definitely doesn't call finalizers.
You don't need to break the cycles to call the finalizers. Just call
them, then collect the whole cycle (assuming it is still unreachable).
The GC will *never* reclaim a reachable object. Objects awaiting
finalization are reachable, by definition.
Well it was sloppily worded, so replace it with:
if a finalizer attempts to access an already finalized object.
A finalized object will still be a valid object.
Python code cannot make an object unsafe.
Obviously C code can make it unsafe, but that's true of C code anywhere.
For example, a file object will close itself during finalization,
but its still a valid object, just a closed file rather than an open one.
Michael
Michael
It may not make a difference for the runtime, but the difference for
user software may be "dead" or "alive".
Stefan
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