From: grundmann <grundema AT uni-duesseldorf DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Memory Problem
Date: Mon, 27 Jul 1998 18:32:10 +0200
Organization: Heinrich Heine Universitaet Duesseldorf
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Eli Zaretskii wrote:

> On Fri, 24 Jul 1998, grundmann wrote:
>
> > I am writing an application that needs lots of memory
> > How can i determin the amount of memory which i can allocate with malloc
> > without getting a NULL pointer ?
>
> The easiest way is to call `_go32_dpmi_remaining_virtual_memory' at
> the very beginning of your program.  This avoids the problems with the
> internal free memory pool maintained by malloc/free, whose size you
> cannot know (at the beginning of the program, this pool has a
> negligible size).
>
> Beware: some DPMI servers won't allow you to allocate all of the free
> memory in a single large chunk.  See the FAQ for details.
>
> > Do i have to configure CWSDPMI sepcial to use 64 MB Ram ( or 96 MB
>
> No.  But you may need to configure your system to allow CWSDPMI access
> to more than 64MB, since some memory managers limit the memory they
> make available to programs.

  Ok then please look at that code :

  fprintf(error_file,"There is still %ld bytes physical
memory\n",_go32_dpmi_remaining_physical_memory());
  fprintf(error_file,"There is still %ld bytes virtual
memory\n",_go32_dpmdi_remaining_virtual_memory());
  buffer_size=_go32_dpmi_remaining_virtual_memory()/3*2;
  fprintf(error_file,"The Buffer size is:%d\n",buffer_size);
  sample_buffer=(short *)SicherAlloc(buffer_size);
  fprintf(error_file,"First chunk allocated\n");
  fprintf(error_file,"There is still %ld bytes physical
memory\n",_go32_dpmi_remaining_physical_memory());
  fprintf(error_file,"There is still %ld bytes virtual
memory\n",_go32_dpmi_remaining_virtual_memory());


void *SicherAlloc(size_t size){
  void *pointer;
  if((int)(pointer=malloc(size))) return pointer;
  fprintf(error_file,"Error Allocating %ld bytes.\n",size);
  exit(1);
}

  And then look at the output which is given in the error_file :

There is still 62693376 bytes physical memory
There is still 69185536 bytes virtual memory
Die Buffer size ist:46123690
First chunk allocated
There is still 62689280 bytes physical memory
There is still 2011136 bytes virtual memory

This is done under dos with CWSDPMI .
Does malloc has such an overhead ? There are about 20 Megabytes of Memory
missing !
The second thing is that i only want physical memory cause i sample from a AD
Card very quick and it is possible that i
loose data when i use swapped mem.
I tried to move the data to disk ( with normal open and write functions ) but
it didn't work . I got an buffer overflow in the
sample buffer of the AD Card .
I move 8 Kilobyte blocks from card to memory and then tried to move them to
disk but without success .