what to do when malloc returns NULL?

[Peter Michaux]

Suppose I have implemented a language with garbage collection in C. I
have wrapped malloc in my own C function. If malloc returns NULL then
I can run the garbage collector and then try malloc again. What do I
do if malloc returns NULL again? Can a C program ask the operating
system for more space and then I could try malloc a third time?

Thanks,
Peter

[Harald van =?UTF-8?b?RMSzaw==?=]

Re: what to do when malloc returns NULL?

On Mon, 24 Mar 2008 22:39:25 -0700, Peter Michaux wrote:

Suppose I have implemented a language with garbage collection in C. I
have wrapped malloc in my own C function. If malloc returns NULL then I
can run the garbage collector and then try malloc again. What do I do if
malloc returns NULL again? Can a C program ask the operating system for
more space and then I could try malloc a third time?

No, or at least, not portably, and I'm not aware of any system-specific
ways. If malloc returns NULL, and you've freed everything that can be
freed, there just isn't enough memory available. One way to handle this
is abort (either the program, or the current operation), and show the
user an error. Another is to pause, asking the user to shut down other
applications. But in the second case, that's not something that the OS
should do automatically.

[Jack.Thomson.v3@gmail.com]

Re: what to do when malloc returns NULL?

Pausing for some time and trying to allocate memory could work, if in
the mean time some memory gets freed.

~Jack
-------------------------------------

http://programmingsite.googlepages.com

On Mar 25, 10:39 am, Peter Michaux <petermich...@g mail.comwrote:

Suppose I have implemented a language with garbage collection in C.  I
have wrapped malloc in my own C function. If malloc returns NULL then
I can run the garbage collector and then try malloc again. What do I
do if malloc returns NULL again? Can a C program ask the operating
system for more space and then I could try malloc a third time?
>
Thanks,
Peter

[Peter Michaux]

Re: what to do when malloc returns NULL?

On Mar 24, 10:46 pm, Harald van D©¦k <true...@gmail. comwrote:

On Mon, 24 Mar 2008 22:39:25 -0700, Peter Michaux wrote:

Suppose I have implemented a language with garbage collection in C. I
have wrapped malloc in my own C function. If malloc returns NULL then I
can run the garbage collector and then try malloc again. What do I do if
malloc returns NULL again? Can a C program ask the operating system for
more space and then I could try malloc a third time?

>
No, or at least, not portably, and I'm not aware of any system-specific
ways.

Well I suppose that is good news in some way. If it is not possible
then don't have to implement it ;-)

Thanks,
Peter

[santosh]

Re: what to do when malloc returns NULL?

Peter Michaux wrote:

Suppose I have implemented a language with garbage collection in C. I
have wrapped malloc in my own C function.
If malloc returns NULL then
I can run the garbage collector and then try malloc again. What do I
do if malloc returns NULL again? Can a C program ask the operating
system for more space and then I could try malloc a third time?

The only way that a portable C program can ask the operating system for
more space for dynamic memory is through the *alloc functions. So you
_could_ keep trying malloc a predefined number of times before bombing
out, but IMHO it's better, in a new language, to use the APIs provided
by the platform for memory management. Often they provide control
beyond what ISO C malloc does.

[santosh]

Re: what to do when malloc returns NULL?

santosh wrote:

Peter Michaux wrote:
>

>Suppose I have implemented a language with garbage collection in C.
>I have wrapped malloc in my own C function.
>If malloc returns NULL then
>I can run the garbage collector and then try malloc again. What do I
>do if malloc returns NULL again? Can a C program ask the operating
>system for more space and then I could try malloc a third time?

>
The only way that a portable C program can ask the operating system
for more space for dynamic memory is through the *alloc functions. So
you _could_ keep trying malloc a predefined number of times before
bombing out, but IMHO it's better, in a new language, to use the APIs
provided by the platform for memory management. Often they provide
control beyond what ISO C malloc does.

OK, seeing Harald's reply I see that I misunderstood your question.
Please excuse.

[CBFalconer]

Re: what to do when malloc returns NULL?

Peter Michaux wrote:

Harald van D©¦k <true...@gmail. comwrote:

>Peter Michaux wrote:
>>

>>Suppose I have implemented a language with garbage collection in
>>C. I have wrapped malloc in my own C function. If malloc returns
>>NULL then I can run the garbage collector and then try malloc
>>again. What do I do if malloc returns NULL again? Can a C program
>>ask the operating system for more space and then I could try
>>malloc a third time?

>>
>No, or at least, not portably, and I'm not aware of any
>system-specific ways.

>
Well I suppose that is good news in some way. If it is not possible
then don't have to implement it ;-)

This illustrates the problems involved in using garbage collection,
which is not what the C system was built to use. There is no way
it can be as efficient as normal use of malloc/free. Which means
you have to pay attention.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.



--
Posted via a free Usenet account from http://www.teranews.com