NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/sys/atari/st/tech/6514

Text File | 1993-01-06 | 2.6 KB | 52 lines

Newsgroups: comp.sys.atari.st.tech
Path: sparky!uunet!spool.mu.edu!wupost!csus.edu!netcom.com!ersmith
From: [e-mail] (Eric R. Smith)
Subject: Re: Malloc (Was: Sending objc_draw to a buffer)
Message-ID: <[e-mail]>
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Wed, 6 Jan 1993 22:49:37 GMT
Lines: 41

In article <[e-mail]> [e-mail] (Leo Hendry) writes:
>In article <[e-mail]> [e-mail] (Eric R. Smith) writes:
>>Most libraries' malloc() functions will handle everything automatically,
>>allocating memory in large chunks (4K or 8K or even 32K) from the OS
>>and then splitting those chunks up as necessary.

>Do you know of any librarys that will Mfree() blocks once all parts of them
>have been free()ed though?  If none do then we have know choice but to use
>Malloc() directly in a multi-tasking system or else the user will have to
>shut down applications and restart them to free "lost" memory.

Yes, some libraries do Mfree() blocks. Most do not. There are advantages
and disadvantages both ways (the advantage of *not* freeing the memory
is speed; if your program needs to malloc() again and the block *is*
freed, then there is an overhead of 2 system calls (Mfree and then another
Malloc).

It is possible that a program will need to do a very large malloc(), free
the memory, and then never need that much memory again. In this case
there could be "lost" memory. I still recommend using your C library
malloc() function, though, because this kind of situation is relatively
rare (and easily special-cased around, i.e. you can use Malloc/Mfree
for specific large blocks of memory that you know you will never need
again).

Programs that use Malloc and Mfree for general purpose memory management
(i.e. that have lots of calls like "foo = Malloc(100L)") are already
slower than they need to be, and will definitely consume far more
memory than necessary under memory protection/virtual memory versions
of MultiTOS or TOS.

Finally, the other advantage of malloc() and free() is portability;
these are standard C functions and so are available in every library
and on every platform, not just the Atari. (I know, that's often not
a concern if you're only writing for the Atari ST, but it never hurts
to make your software easy to port to other machines or operating
systems.)

Eric Smith    [e-mail]
Opinions expressed above are my own; Atari has their own opinions, I'm sure.