C garbage collection -crazy idea

[onkar]

This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()
then is it not a garbage collection (in the first place , garbage will
not be generated !! ) . Is it
possible to have a compiler with such feature. Or if Its not a good
idea (or may be this is an idiotic idea) please tell me why is it so ??

Thanks,

[Zealot Zuo]

onkar wrote:

This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()
then is it not a garbage collection (in the first place , garbage will
not be generated !! ) . Is it
possible to have a compiler with such feature. Or if Its not a good
idea (or may be this is an idiotic idea) please tell me why is it so ??

Thanks,

Fun idea though, but I think you may try C++ auto_ptrs.
I don't think auto-free would be wrote into C standards.

[Chris Dollin]

onkar wrote:

This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()
then is it not a garbage collection (in the first place , garbage will
not be generated !! ) . Is it
possible to have a compiler with such feature. Or if Its not a good
idea (or may be this is an idiotic idea) please tell me why is it so ??

How is the compiler supposed to know /where/ to add the `free` call?

--
Chris "halting problem" Dollin
The shortcuts are all full of people using them.

[Richard Heathfield]

onkar said:

This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()

....then you wouldn't be able to use it for translating any existing C
programs that correctly call free().

And how would it know when to call free()? I'll be the judge of that, thank
you.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.

[goose]

onkar wrote:

This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()
then is it not a garbage collection (in the first place , garbage will
not be generated !! ) . Is it
possible to have a compiler with such feature. Or if Its not a good
idea (or may be this is an idiotic idea) please tell me why is it so ??

How would the compiler react to this?

int x, i;
....
int **foo = malloc (sizeof *foo * x);
....
for (i=0; i<x; i++) {
foo[i] = malloc (sizeof *foo[i]);
}
....

How many calls to free should there be, and where should
they be placed?

goose,
google for Boehm GC for C.

[Chris Dollin]

Richard Heathfield wrote:

onkar said:

>This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()

...then you wouldn't be able to use it for translating any existing C
programs that correctly call free().

If -- I say /if/ -- the compiler could correctly deduce where to put
the matching malloc, then it could also discard the explicit calls
to free.

And how would it know when to call free()? I'll be the judge of that, thank
you.

Verily. (For values of "verily" that mean "GC is wonderful and the
machine can do a better job of store management than I can, but C
isn't meant for the kind of programs that benefit -- if I have a GC
environment I'm sure as heck that I won't waste it on writing C
when there are lots of GC-exploiting idioms I could be using instead.")

--
Chris "short word, long meaning" Dollin
"Our future looks secure, but it's all out of our hands"
- Magenta, /Man and Machine/

[Chris Dollin]

Chris Dollin wrote:

If -- I say /if/ -- the compiler could correctly deduce where to put
the matching malloc,

The matching /free/.

What idiot wrote that snippet?

--
Chris "rhetorical " Dollin
"- born in the lab under strict supervision -", - Magenta, /Genetesis/

[Kohn Emil Dan]

On Fri, 15 Dec 2006, onkar wrote:

This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()

The question is *when* to insert the call to free(). When the function
that called malloc() returns? But in many cases memory allocated via
malloc() is used even after the function that performed the allocation
returns. So, in order to know when it is appropriate to call free(), you
need a more elaborate scheme (reference counting and tracking) which is
what a garbage collector does.

then is it not a garbage collection (in the first place , garbage will
not be generated !! ) . Is it
possible to have a compiler with such feature. Or if Its not a good
idea (or may be this is an idiotic idea) please tell me why is it so ??

Garbage collectors incur a run-time penalty. Therefore most C
implementations won't use it. However, the C language by itself does not
explicitly forbid using garbage collection. In fact there are some
performant implementations of garbage collectors available.

See the following link for an implementation of a garbage collector for C
and C++.

http://www.hpl.hp.com/personal/Hans_Boehm/gc/
Emil

>
Thanks,

[Roland Pibinger]

On Fri, 15 Dec 2006 11:36:33 +0000, Chris Dollin wrote:

>onkar wrote:

>If a compiler is designed such that it automatically adds a free()
matching every malloc()
then is it not a garbage collection (in the first place , garbage will
not be generated !! ) . Is it
possible to have a compiler with such feature. Or if Its not a good
idea (or may be this is an idiotic idea) please tell me why is it so ??

How is the compiler supposed to know /where/ to add the `free` call?

The compiler just needs to add the 'free' call(s) in the same scope in
which *alloc is called (in inverse order). When a pointer to allocated
memory is returned from the scope no call to free has to be performed.
I guess that would not be difficult to implement but is not compatible
to current C and therefore unrealistic.

Best wishes,
Roland Pibinger

[af]

I wouldn't say automatic placing of free() statements is a *crazy*
idea. To my point of view, this is a good idea, first. �

I believe It is quite possible to detect a lot of places where to add
free() with static code analysis. I can do it by examining code, so the
clever program also should be able to do this. It would save a lot of
$$ to issue at least a warning for such case. The only problem is
compiler developers are too busy to develop such checks, and static
code analyzers repay their high price.

I know the only free tool for static code analysis [1], and it is
unable to validate memory allocation. Probably one can improve it in
this direction. BTW, there are plenty of runtime leak detectors such as
[2].

[1] CCCC tool, http://sourceforge.net/projects/cccc
[2] Leaky, http://lxr.mozilla.org/mozilla/sourc...aky/leaky.html

With best regards,
Alexei

"""onkar пи�ал(а):
"""

This idea might be vey crazy. But I hope to get answers to this .. from
comp.lang.c

If a compiler is designed such that it automatically adds a free()
matching every malloc()
then is it not a garbage collection (in the first place , garbage will
not be generated !! ) . Is it
possible to have a compiler with such feature. Or if Its not a good
idea (or may be this is an idiotic idea) please tell me why is it so ??

Thanks,