On Fri, 20 Nov 2009 19:24:05 +0300, dsimcha <[email protected]> wrote:
== Quote from Travis Boucher ([email protected])'s article
dsimcha wrote:
> == Quote from Denis Koroskin ([email protected])'s article
>> On Fri, 20 Nov 2009 17:28:07 +0300, dsimcha <[email protected]>
wrote:
>>> == Quote from Travis Boucher ([email protected])'s article
>>>> dsimcha wrote:
>>>>> == Quote from Travis Boucher ([email protected])'s article
>>>>>> Sean Kelly wrote:
>>>>>> Its harder
>>>>>> to create a memory leak in D then it is to prevent one in C.
>>>>> void doStuff() {
>>>>> uint[] foo = new uint[100_000_000];
>>>>> }
>>>>>
>>>>> void main() {
>>>>> while(true) {
>>>>> doStuff();
>>>>> }
>>>>> }
>>>>>
>>>> Hmm, that seems like that should be an implementation bug.
Shouldn't
>>>> foo be marked for GC once it scope? (I have never used new on a
>>>> primitive type, so I don't know)
>>> It's conservative GC. D's GC, along with the Hans Boehm GC and
probably
>>> most GCs
>>> for close to the metal languages, can't perfectly identify what's a
>>> pointer and
>>> what's not. Therefore, for sufficiently large allocations there's
a high
>>> probability that some bit pattern that looks like a pointer but
isn't
>>> one will
>>> keep the allocation alive long after there are no "real" references
to
>>> it left.
>> Aren't uint array allocations have hasPointers flag set off? I always
>> thought they aren't scanned for pointers (unlike, say, void[]).
>
> Right, but they can still be the target of false pointers. In this
case, false
> pointers keep each instance of foo[] alive, leading to severe memory
leaks.
But the issue is more of a GC implementation issue then a language
issue, correct?
Yes.
Or is this an issue of all lower level language garbage
collectors?
Kinda sorta. It's possible, but not easy, to implement fully precise GC
(except
for the extreme corner case of unions of reference and non-reference
types) in a
close to the metal, statically compiled language.
Unions could be deprecated in favor of tagged unions (see an example in
Cyclone http://cyclone.thelanguage.org/wiki/Tagged%20Unions). Would that
help?
