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From: [e-mail] (Robin Rosenberg)
Newsgroups: comp.lang.c++
Subject: Re: Would/Won't you use a garbage collector?
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Date: 10 Apr 96 08:09:08 GMT
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Giuliano Carlini wrote:
>
> I'm a long time proponent of using garbage collection in C and C++
> programs, and I'm curious:
>         - How many others are there?Count One. It was no problem to use it and it was fairly fast. It was
a small compiler. Version one was a command-line program that only
allocated memory until it was finished and then the whole program exited.
The second version was a Windoze version and suddenly memory had to be
freed between invocations. Using GC was very handy and appropriate.

>         - Why don't most C/C++ programmers use it?If you are not 100% sure it will work, you will put your project at
risk. Secondly your program will use more memory with GC than it
would otherwise (unless your memory leaks are severe). Alternatively
you could perform GC very often at the cost of CPU and response time.

> I'm particularly interested in finding out why most C/C++ don't use it.
> While I have my own theories - which I'll describe below - I'm
> interested
> in finding out more directly from those who are against it. I've spent
> a
> good part of the past 4 years trying to convince people to use it, and
> I've got a handle on why the small group of people I associate with are
> not using it, but I'd like to find out more about why the C/C++
> community
> as a whole does not.

Memory is but one resource. The other resources are trickier
as they often have to be freed in a particular order and conservative
GC's have their own ideas of when to free resources and their order.
Secondly if you use global things like notifications (as in MVC) you
will end up managing your resources explicitly anyway. Weak pointers
may help there but you have to design for that and the reason for using
GC was that you didn't want to bother in the first place.

Secondly GC assumes you can take over memory management in the whole
application. How about shared libraries (DLL's etc). You don't want
to static linke (even if you could) your whole application.

> I hope that with this information, I'll be able to perfect a more
> convincing presentation for why the default should be to use garbage
> collection, and for why explicit calls to free/delete should be used
> only
> in the rare cases for which garbage collection is inappropriate.
>
> What follows is my belief for why garbage collection is so little used.
> Feel free to respond to anything I say below, but please, first respond
> to the questions above. I believe that most people don't use garbage
> collection because either they:
>         - don't know what it is
>         - don't know it can be used with C/C++.
>         - are misinformation
>         - are biased against it by the C/C++ culture

Probably true on all points. Regarding the last point, one might add that
GC is not a replacement for proper design, which also solves the memory
managemnt problem, sometimes at a higher design expense.

> In my experience, most C/C++ programmers either don't know what garbage
> collection is, or don't know that it can be used with C/C++. After all,
> no major C/C++ compiler includes a garbage collector. At least, as far
> as I know. I hope I'm wrong, and that someone can correct me. But even
> after, I tell them what it is, and that it can be used with C++, almost
> everyone still rejects it.

One think is that most GC's are free or shareware with little or no support
and very few programmers are capable of troubleshooting problems related to
GC. A light can be seen at the other end of the tunnel, though. I saw an ad
in Object Magazine for a company that claims to have a plug-and-play GC for
sale.

> At first, most offer technical reasons for rejecting it. Almost all are
> based on misinformation, since garbage collection is usable and
> benificial
> for the vast majority of systems. The most often mentioned is that
>[.strange jump in article.]
[...]
>inventory control. And what else is memory deallocation but a sort of
>bookkeeping or inventory control. It's just that rather than being for
>a resource outside of the computer it is for one inside.

You can also use the idea of ownership (has-relations or whatever
you call it). Make sure you always have an owner to your objects and
make sure the owner deletes everything it owns. That goes a long
way towards ridding yourself of memory leaks. auto_ptr and similar
idioms are also a must.

>For anyone who may be wondering, I believe that we should use garbage
>collection because:
>        - It vastly decreases the number of bugs in programs which use
>it.

but it can introduce very subtle bugs. Since GC can happen at "any"
time it is hard to find out what is the problem when problems occur.

>        - It vastly decreases the time to complete programs which use
>it.

More or less true.

>        - It vastly increases the understandability, reuseability,
>                extensability, and maintainability of programs which use
>it.

Indeed. A lot of code can be removed. One should always consider GC.

>So, do you use garbage collection in your C/C++ programs, and if not,
>why not?

>giuliano--
Robin Rosenberg,  | Voice: [phone] | OO consulting, education
Enator Objective  | Fax:   [phone] | and mentoring since
 Management AB    | Mail:  [e-mail] | 1985.
"Any opinions above are my own *personal* opinions, etc. etc."