----- Ursprüngliche Nachricht -----
Von: Sergio Campamá
Gesendet am: 22 Aug 2011 13:36:07
> So the problem is not really malloc, but free
Interesting
I'll give that a
> look. Thanks!
Actually, it's the way malloc/free works.
Putting a nail neatly into a tire doesn't give you a flat tire. But if you pull
it out again...
Using only malloc does just waste a few bytes (at least two, depending on
implementation)
for organizational issues.
In this case an plain incremental malloc that just keeps the address of the
first unused byte
on the heap would be way more effective (and faster). But you could never free
ram again.
However, malloc does offer freeing ram and has to keep the overhead, even if
you don't use it.
Moreover, it needs to follow the chain of malloced areas to find the first free
one. Which is
(relatively) slow.
And I doubt the MSP implementation has an algorithm to search for the best
fitting hole,
using the first that is large enough. Which increases heap congestion for
different-sized
mallocs.
However, a plain malloc version should be easy to implement yourself. Just
start using
ram where the last variable ends, and keep a pointer to the first unused byte.
(which is
the pointer to the first byte of the next allocated space)
No need to link malloc/free anymore, making your code smaller too.
On Aug 22, 2011, at 7:30 AM, JMGross wrote:
> ----- Ursprüngliche Nachricht -----
> Von: Sergio Campamá
> An: mspgcc-users@lists.sourceforge.net
> Gesendet am: 19 Aug 2011 17:53:45
> Betreff: Re: [Mspgcc-users] RAM Management
>
>> Thanks for the insight into the problem. The thing is that I have a task
>> scheduler, a linked list that, well, lists the tasks to perform... Since
>> linked lists are dynamic in nature, I need malloc to create the new "task"
>> and append it to the list.. And after the task is done, I free the task and
>> go on to the next one... The other place I use linked lists is to maintain
>> a list of timers that the application uses to signal certain events... after
>> the timer activates, it also gets freed...
>
>> So that is why I need malloc and can't (or don't know how) to do it with
>> other types of dynamic storage, or static. (On that subject, what other
>> types of dynamic storage exist?)
>
> You can use a semi-dynamic linked list.
> When a list element is freed, don't free it, just cut it from the list and
> append it to the end with a 'null task' entry.
> So when a new task comes up, the already allocated list element
> is found after the 'active' ones and can be reused. If the list is full,
> you can malloc another element and append it
> (the list grows if necessary), but you never free it again.
> The list won't grow larger than required, bu twill not cause heap
> congestion.
> Also, it might be more performant (depending on your list
> concatenation management, e.g. keep a pointer to the first free
> element, etc.)
>
> JMGross
>
>
>
>
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