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xmalloc string functions

 
 
ymuntyan@gmail.com
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      02-07-2008
On Feb 6, 6:22 pm, "Herbert Rosenau" <(E-Mail Removed)> wrote:
> On Thu, 31 Jan 2008 22:47:37 UTC, (E-Mail Removed) wrote:
> > On Jan 31, 2:26 pm, "Herbert Rosenau" <(E-Mail Removed)> wrote:
> > > On Tue, 29 Jan 2008 08:12:51 UTC, (E-Mail Removed) wrote:
> > > > There is nothing to recover because failure of fopen()
> > > > is a normal situation. Absolutely different from a failure
> > > > of malloc() when you are trying to allocate a structure
> > > > to push into the event queue to scroll text a bit later.

>
> > > There is no difference at all. When I can't open a file I will tell my
> > > caller that fact like I do when malloc() fails to delever me the
> > > amount of memory I ask it for.

>
> > > The caller will check the error condition it receives and will react
> > > properly on that and then tell its caller the the error when it is
> > > unable himself to recover from that error to continue as it should
> > > when possible. Its caller does the same until there is a point that is
> > > either
> > > - action is complete undone - clean state
> > > normal work goes on
> > > - action is complete undone - no chance to to contine normal run
> > > shut down program cleanly - a restart of the progam may be more
> > > successfull

>
> > > There is nothing that requires an abort() or exit() abnormally.

>
> > What exactly are you talking about here? If you do shut down
> > the program then you do shut it down, that's it. Whether you
> > do it up the stack in the main() or in the memory allocator
> > may or may not be different. If it's not different, then it
> > 1) doesn't make much sense to unwind the stack;
> > 2) actually is more expensive to unwind the stack: the more
> > code the more bugs you got.
> > Where it's not true, it's not true.

>
> exit() does NOT write buffers not already given into the stream,
> save data local to the functions in the call chain,
> lots of other work a clean shutdown has to do.


Depends, doesn't it? You don't have to flush buffers
if you are not writing anything. You don't have to
flush buffers if you are writing a temporary file and
your writer is not going to succeed. Not sure what it
means to "save data local to the functions", but that
may or may not be needed. You certainly don't need to
free() your allocated blocks if your process is going
to die now (it's not a general situation, remember?)

Lots and lots of work is done on clean shutdown, certainly.
Much of that work needs memory too. You can do it?
Great, do it. You can't? Well, you insist on trying
anyway, I am saying it's pointless.

> However catching any error (including malloc() fails) is a must.


Yup.

>
> > > Sure, it costs a bit more to get a program failsave - but it saves
> > > lots of money, lots of time and holds customer because no customer
> > > will ever complain because the program aborts, looses or destroy work
> > > or data only because the programmer was crazy enough to kill its
> > > program only because there was a moment where an open() faild, there
> > > was for a period of time not enough memory to allocate a small big or
> > > very big amount of memory to get a single action done.

>
> > > It makes always sense to check malloc() for success - because this
> > > saves a lot of money for useless maintenance, earning annouyed
> > > customers, ending up in loosing trust.

>
> > Right, malloc() result must always be checked. Except it doesn't
> > imply your code must be cluttered with if() for every call to
> > whatever_func_you_use_to_allocate_memory().

>
> Ah, you means really that you should never check for error but
> shorthand exit() when an fopen() fails, a fread() or fwrite() can't do
> its job its asced for? Becausae you code gets cluddered on if on that?


No, I didn't mean that.

>
> By that my code is full of fuctions designed to use in that program
> only once - because these functions are designed to hide details of
> work frm the process through the action.
>
> > > This is completely false. Even a guy application can handle any lack
> > > of memory well without the need to crash the whole app.

>
> > Right, it can. Except it can't draw if it doesn't have
> > memory to draw. I don't care if the application is still
> > up if it doesn't display the stuff it's supposed to display.
> > Nor do I care how it exits on OOM, using abort() or exit(0)
> > or exit(EXIT_FAILURE); does it exit from main() after everything
> > properly returned an error or right in the draw_thingie()
> > call (AFTER it properly cleaned up its crap, how about that?).

>
> There is no need to exit() or abort() a failsave app.


Failsafe application? It won't fail, that's true. I don't
think I am talking about failsafe applications though.

> You can't draw?
> Defere the action until you can do it again.


Good one.

> It doesn't matter why you
> can't. In some time later you'll be able to do the the job.


Yeah. Hope and you'll get what you need.

> You can't
> show an error to the user? Hi, your log will show that fact.


What is that log again?

>
> However only the caller or one of its parents in the chain will know
> how to handle the failture "no memory" in a usefull way.


BS. Why is it everybody obsessed with "callers" and "parents"?
Sounds like you have no idea about how gui applications work.

> There is a
> need to unwind the stack until the error can be handled useful. Hey,
> only that may give you the needed resources to interact with the user
> or other parter your program interacts with.


Yep, main() will get more memory to the toolkit_main_loop()
function.

>
> However when your program comes in a situation where it can't continue
> the active action because lack of resorce needed unwind until it is in
> the state "nothing done yet" again. Then redo the same thing may end
> successfull or fail again. Depending on the current environment there
> can be a chance to retry, defere to later or simply shut down clean.
> But in any way there is no need to exit() or abort() only because a
> resource needed to continue is unavailable yet.


Try harder and you'll succeed! There are no situations where
you should fail! Did I get it right?

> At least it doesn't matter if a job can't success because lack of
> resource (menory, handles, atoms, or whatever else), important is that
> the app gets back to a state it is able to save anything worth to get
> saved before it gets lost.


Application shouldn't lose data, absolutely. And? Banana
and apple are fruits. Yep.

Anyway, let me make things easier for you and others,
so you don't have to read what I didn't write.

================================================== ======
= Wisdom starts here

The only thing an application can do when malloc() fails
is abort(). Any application, in any situation. In fact,
applications should use the following API to be robust
and for user data to be safe:

void *alloc_or_die(size_t n)
{
void *ptr = malloc(n);
if (!ptr)
abort();
return ptr;
}

FILE *fopen_or_die(const char *filename, const char *mode)
{
FILE *file = fopen(filename, mode);
if (!file)
abort();
return file;
}

I got more, but I think you get the idea.
 
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