Garbage collection in C++

[pushpakulkar@gmail.com]

Hi all,

Is garbage collection possible in C++. It doesn't come as part of
language support. Is there any specific reason for the same due to the
way the language is designed. Or it is discouraged due to
some specific reason. If someone can give inputs on the same, it will
be of great help.

Regards,
Pushpa

[Chris M. Thomasson]

Re: Garbage collection in C++

<pushpakulkar@g mail.comwrote in message
news:22b430aa-4990-4dcf-9e2f-9e828427986c@a2 9g2000pra.googl egroups.com...

Hi all,
>
Is garbage collection possible in C++.

Sure:

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

It doesn't come as part of
language support. Is there any specific reason for the same due to the
way the language is designed. Or it is discouraged due to
some specific reason. If someone can give inputs on the same, it will
be of great help.

C++ is a low-level systems language, IMVHO, that's no place for a GC to
be...

[Bharath]

Re: Garbage collection in C++

On Nov 15, 10:32 am, "Chris M. Thomasson" <n...@spam.inva lidwrote:

<pushpakul...@g mail.comwrote in message
>
news:22b430aa-4990-4dcf-9e2f-9e828427986c@a2 9g2000pra.googl egroups.com...
>

Hi all,

>

Is garbage collection possible in C++.

>
Sure:
>

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

>

It doesn't come as part of
language support. Is there any specific reason for the same due to the
way the language is designed. Or it is discouraged due to
some specific reason. If someone can give inputs on the same, it will
be of great help.

>
C++ is a low-level systems language, IMVHO, that's no place for a GC to
be...

Check out: http://www.research.att.com/~bs/bs_f...age-collection

- bharath

[Juha Nieminen]

Re: Garbage collection in C++

pushpakulkar@gm ail.com wrote:

Is garbage collection possible in C++. It doesn't come as part of
language support. Is there any specific reason for the same due to the
way the language is designed. Or it is discouraged due to
some specific reason. If someone can give inputs on the same, it will
be of great help.

I have absolutely no experience in third-party garbage collectors for
C++. What I have always wondered, though, is how those can handle a
situation like:

int* foo()
{
int* table = new int[100];
return table+40;
}

The pointer to the beginning of the allocated array dies when foo()
terminates, but a pointer to one of its elements lives beyond the scope
of foo(). This pointer may be used in the calling code. A garbage
collector would have to:

1) Know that there's still a live pointer pointing to (an element
inside) the array, and thus it cannot destroy it yet.

2) Know to delete the array properly (ie. from the original pointer
pointing to the beginning of the array, rather than the one which lived
longer than that) when that returned pointer dies and the GC runs.

I suppose they have figured out these problems. I'm just wondering how.

[Pete Becker]

Re: Garbage collection in C++

On 2008-11-15 12:21:06 -0500, Juha Nieminen <nospam@thanks. invalidsaid:

>
I have absolutely no experience in third-party garbage collectors for
C++. What I have always wondered, though, is how those can handle a
situation like:
>
int* foo()
{
int* table = new int[100];
return table+40;
}
>
The pointer to the beginning of the allocated array dies when foo()
terminates, but a pointer to one of its elements lives beyond the scope
of foo(). This pointer may be used in the calling code. A garbage
collector would have to:
>
1) Know that there's still a live pointer pointing to (an element
inside) the array, and thus it cannot destroy it yet.
>
2) Know to delete the array properly (ie. from the original pointer
pointing to the beginning of the array, rather than the one which lived
longer than that) when that returned pointer dies and the GC runs.
>
I suppose they have figured out these problems. I'm just wondering how.

It's just a bit of bookkeeping. When the array is allocated the
collector makes notes about the size of the allocated block and where
it begins. The returned pointer points into the allocated block, so the
block is still live.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Joe Smith]

Re: Garbage collection in C++


<pushpakulkar@g mail.comwrote in message
news:22b430aa-4990-4dcf-9e2f-9e828427986c@a2 9g2000pra.googl egroups.com...

Hi all,
>
Is garbage collection possible in C++. It doesn't come as part of
language support. Is there any specific reason for the same due to the
way the language is designed. Or it is discouraged due to
some specific reason. If someone can give inputs on the same, it will
be of great help.

The C++ standardization commitee is working with some garbage collection
related proposals,
although no official garbage collection mechanism will be included in C++0x.
It is not yet clear
if the auxillary proposal to make it easier to support garbage collection
via third party libraries
will be approved for C++0x or not.

[Pete Becker]

Re: Garbage collection in C++

On 2008-11-15 13:44:20 -0500, "Joe Smith" <unknown_kev_ca t@hotmail.comsa id:

>
<pushpakulkar@g mail.comwrote in message
news:22b430aa-4990-4dcf-9e2f-9e828427986c@a2 9g2000pra.googl egroups.com...

Hi

>

>all,
>>
>Is garbage collection possible in C++. It doesn't come as part of
>language support. Is there any specific reason for the same due to the
>way the language is designed. Or it is discouraged due to
>some specific reason. If someone can give inputs on the same, it will
>be of great help.

>
The C++ standardization commitee is working with some garbage
collection related proposals,
although no official garbage collection mechanism will be included in
C++0x. It is not yet clear
if the auxillary proposal to make it easier to support garbage
collection via third party libraries
will be approved for C++0x or not.

It's quite clear, since it was approved at the September meeting. <g>
Search for "safely derived pointer" in the current working draft.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Joe Smith]

Re: Garbage collection in C++


"Pete Becker" <pete@versatile coding.comwrote in message
news:2008111514 561516807-pete@versatilec odingcom...

On 2008-11-15 13:44:20 -0500, "Joe Smith" <unknown_kev_ca t@hotmail.com>
said:

>The C++ standardization commitee is working with some garbage collection
>related proposals,
>although no official garbage collection mechanism will be included in
>C++0x. It is not yet clear
>if the auxillary proposal to make it easier to support garbage collection
>via third party libraries
>will be approved for C++0x or not.

>
It's quite clear, since it was approved at the September meeting. <g>
Search for "safely derived pointer" in the current working draft.
>

Roger that, I should have been more clear that it was not clear to me
if the auxillary proposal was included. I'm trying to follow things, but
I am not reading every posted paper, so I may well miss things.

[Chris M. Thomasson]

Re: Garbage collection in C++

"Chris M. Thomasson" <no@spam.invali dwrote in message
news:7OCTk.31$m 74.24@newsfe24. iad...

<pushpakulkar@g mail.comwrote in message
news:22b430aa-4990-4dcf-9e2f-9e828427986c@a2 9g2000pra.googl egroups.com...

>Hi all,
>>
>Is garbage collection possible in C++.

>
Sure:
>

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

>
>
>
>

>It doesn't come as part of
>language support. Is there any specific reason for the same due to the
>way the language is designed. Or it is discouraged due to
>some specific reason. If someone can give inputs on the same, it will
>be of great help.

>
C++ is a low-level systems language,

C++ is nice because it allows the user to apply just enough of its features
to get the job done. You can use C++ for kernel programming; just not all of
it...

;^D

IMVHO, that's no place for a GC to be...

[James Kanze]

Re: Garbage collection in C++

On Nov 15, 4:57 pm, pushpakul...@gm ail.com wrote:

Is garbage collection possible in C++.

Yes and no. There are, in fact, a few constructs which could
break it, and there are potential compiler optimizations which
could prevent it from being used.. In practice, the language
constructs are recognized as poor programming practice, and
something to be avoided, regardless, and compilers don't do
optimizations which would break it, and in fact, it is more or
less widely used; see
http://www.hpl.hp.com/personal/Hans_Boehm/gc/.

It doesn't come as part of language support. Is there any
specific reason for the same due to the way the language is
designed. Or it is discouraged due to some specific reason. If
someone can give inputs on the same, it will be of great help.

More history than any other reasons. It's readily available,
and works, and is being used by a number of people.

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

[James Kanze]

Re: Garbage collection in C++

On Nov 15, 5:32 pm, "Chris M. Thomasson" <n...@spam.inva lidwrote:

<pushpakul...@g mail.comwrote in message

news:22b430aa-4990-4dcf-9e2f-9e828427986c@a2 9g2000pra.googl egroups.com...

Is garbage collection possible in C++.

Sure:

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

It doesn't come as part of language support. Is there any
specific reason for the same due to the way the language is
designed. Or it is discouraged due to some specific reason.
If someone can give inputs on the same, it will be of great
help.

C++ is a low-level systems language, IMVHO, that's no place
for a GC to be...

C++ is a multi-paradigm language, usable in many contexts. If
you're writing kernel code, a garbage collector certainly has no
place; nor do exceptions, for that matter. And if you're
implementing a garbage collector, obviously, you can't use it.
But for most application programs, it's stupid not to.

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

[George Kettleborough]

Re: Garbage collection in C++

On 15/11/08 15:57, pushpakulkar@gm ail.com wrote:

Hi all,
>
Is garbage collection possible in C++. It doesn't come as part of
language support. Is there any specific reason for the same due to the
way the language is designed. Or it is discouraged due to
some specific reason. If someone can give inputs on the same, it will
be of great help.
>
Regards,
Pushpa

A related question if I may: Is garbage collection necessary if the
programmer follows a strict RAII design ie. only allocating and
deallocating resources in constructors and destructors? Is garbage
collection just to enable you to program more like Java ie. creating
objects on the heap by using new everywhere? What is the advantage of this?

Java also has the finally block, and I understand this won't be
implemented in C++(0x) any time soon because it's not necessary with
RAII. Can garbage collection in C++ work to the same extent as it does
in Java without the finally block?

--
George Kettleborough

[Ian Collins]

Re: Garbage collection in C++

George Kettleborough wrote:

On 15/11/08 15:57, pushpakulkar@gm ail.com wrote:

>Hi all,
>>
>Is garbage collection possible in C++. It doesn't come as part of
>language support. Is there any specific reason for the same due to the
>way the language is designed. Or it is discouraged due to
>some specific reason. If someone can give inputs on the same, it will
>be of great help.
>>
>Regards,
>Pushpa

>
A related question if I may: Is garbage collection necessary if the
programmer follows a strict RAII design ie. only allocating and
deallocating resources in constructors and destructors? Is garbage
collection just to enable you to program more like Java ie. creating
objects on the heap by using new everywhere? What is the advantage of this?
>

GC and RAII are orthogonal concepts.

Java also has the finally block, and I understand this won't be
implemented in C++(0x) any time soon because it's not necessary with
RAII. Can garbage collection in C++ work to the same extent as it does
in Java without the finally block?
>

Yes.

--
Ian Collins

[James Kanze]

Re: Garbage collection in C++

On Nov 16, 8:38 am, George Kettleborough
<g.kettleboro.. .@member.fsf.or gwrote:

On 15/11/08 15:57, pushpakul...@gm ail.com wrote:

Is garbage collection possible in C++. It doesn't come as
part of language support. Is there any specific reason for
the same due to the way the language is designed. Or it is
discouraged due to some specific reason. If someone can give
inputs on the same, it will be of great help.

A related question if I may: Is garbage collection necessary
if the programmer follows a strict RAII design ie. only
allocating and deallocating resources in constructors and
destructors?

It rarely makes sense to allocate memory in constructors and
deallocate in destructors. If that's what you're doing, it's
generally preferable to use an object directly, with no dynamic
allocation. There are exceptions, of course, but they're a lot
less frequent than people make out. The main motivation for
using dynamic allocation is precisely because the lifetime of
the object must be arbitrary, and doesn't fit any pre-defined
pattern.

Is garbage collection just to enable you to program more like
Java ie. creating objects on the heap by using new everywhere?
What is the advantage of this?

At the lowest level, garbage collection has two major effects:
it allows memory which can no longer be accessed to be reused
(without programmer intervention), and it forbids memory which
can still be accessed from being reused. The first results in
less work for the programmer in a number of specific instances;
it isn't the panacea that some Java proponents would have us
believe, but every little bit helps. The second results in more
robust programs; the memory for one object can't be reused for
another object due to a premature delete. (Premature delete is
a bug that can be exploited to break security, so you definitly
want garbage collection for this reason if your program connects
directly to the Internet.)

Java also has the finally block, and I understand this won't
be implemented in C++(0x) any time soon because it's not
necessary with RAII. Can garbage collection in C++ work to the
same extent as it does in Java without the finally block?

What does garbage collection have to do with the finally block?
For that matter, at the level garbage collection works, what is
the difference between a finally block and the destructor of a
local object?

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

[George Kettleborough]

Re: Garbage collection in C++

On 16/11/08 09:43, James Kanze wrote:

On Nov 16, 8:38 am, George Kettleborough
<g.kettleboro.. .@member.fsf.or gwrote:

>On 15/11/08 15:57, pushpakul...@gm ail.com wrote:

>

>>Is garbage collection possible in C++. It doesn't come as
>>part of language support. Is there any specific reason for
>>the same due to the way the language is designed. Or it is
>>discouraged due to some specific reason. If someone can give
>>inputs on the same, it will be of great help.

>

>A related question if I may: Is garbage collection necessary
>if the programmer follows a strict RAII design ie. only
>allocating and deallocating resources in constructors and
>destructors?

>
It rarely makes sense to allocate memory in constructors and
deallocate in destructors. If that's what you're doing, it's
generally preferable to use an object directly, with no dynamic
allocation. There are exceptions, of course, but they're a lot
less frequent than people make out. The main motivation for
using dynamic allocation is precisely because the lifetime of
the object must be arbitrary, and doesn't fit any pre-defined
pattern.

How would you implement something like a vector without dynamically
allocated memory? I thought dynamically allocated memory was used
because the amount of memory needed can only be decided at run time.

>Is garbage collection just to enable you to program more like
>Java ie. creating objects on the heap by using new everywhere?
>What is the advantage of this?

>
At the lowest level, garbage collection has two major effects:
it allows memory which can no longer be accessed to be reused
(without programmer intervention), and it forbids memory which
can still be accessed from being reused. The first results in
less work for the programmer in a number of specific instances;
it isn't the panacea that some Java proponents would have us
believe, but every little bit helps. The second results in more
robust programs; the memory for one object can't be reused for
another object due to a premature delete. (Premature delete is
a bug that can be exploited to break security, so you definitly
want garbage collection for this reason if your program connects
directly to the Internet.)

I suppose what I don't get is why you would ever want to create objects
on the stack. It's something you can't do in Java, and it's much quicker
to create them on the stack plus they get destructed automatically when
the go out of scope.

>Java also has the finally block, and I understand this won't
>be implemented in C++(0x) any time soon because it's not
>necessary with RAII. Can garbage collection in C++ work to the
>same extent as it does in Java without the finally block?

>
What does garbage collection have to do with the finally block?
For that matter, at the level garbage collection works, what is
the difference between a finally block and the destructor of a
local object?

Well, if you are using new in a try block, and an exception is thrown,
C++ will guarantee the destruction of the pointer and anything else on
the stack but it won't call delete for what you allocated there. I
thought the finally block was to "clean up" any resources you allocated
in the try block, something that isn't necessary if you don't
dynamically allocate resources in there (but instead in the constructors
of objects create there, which are guaranteed to be destroyed).

Maybe I have got this all wrong and I am confusing myself, forgive me
because I'm only just beginning to really learn C++!

--
George Kettleborough