Is this the right way to determine available heap?

[Nick.SIMON at syntegra.bt.co.uk]

I'm no expert (& I don't use GDB) but when I looked at the FAQ's suggestion
on heap sizing, it seemed to me that it'd only work if the heap was
unfragmented.  We really nees something that goes down the list of free
blocks totting up the total size available.

Thinking about your crash, I have encountered mallocs which go horribly
wrong on a request for no memory (zero bytes).


-- Nick Simon 

> -----Original Message-----
> From: OUTWATER [mailto:vac4050 at cae597.rsc.raytheon.com]
> Sent: 26 July 2000 16:56
> To: rtems-users at oarcorp.com
> Subject: Is this the right way to determine available heap?
> 
> 
> All-
> 
> The GDB command 
> 
> p *((Region_Control 
> *)_Region_Information->local_table[1])->Memory->first
> 
> was shown in the  RTEMS Frequently Asked Questions Manual as 
> a way to determine the 
> amount of heap remaining.
> 
> I'm debugging an application and I start with this much heap:
> $1 = {back_flag = 0x8d, front_flag = 0x40c, next = 0x3c6514, 
> previous = 0x17bdf4} 
> using the command in the FAQ.
> 
> But doing this: 
> p *((Region_Control 
> *)_Region_Information->local_table[1])->Memory->last
> 
> returns 
> $2 = {back_flag = 0x1, front_flag = 0x23bdf8, next = 
> 0x17bdf8, previous = 0x3cd798}
> which seems more like what I expect.
> 
> When I run my application (tclsh), it crashes with this 
> backtrace snippet:
> #0  0x400 in _uhoh ()
> #1  0x20100017 in ?? ()
> #2  0x96f80 in _API_extensions_Run_postswitch ()
>     at 
> ../../../../../../../rtems-4.5.0-beta3/c/src/exec/score/src/ap
> iext.c:100
> #3  0x8e7ee in _Thread_Dispatch () at 
> ../../../../../../../rtems-4.5.0-beta3/c/src/exec/score/src/th
readdispatch.c:126
> #4  0x84776 in _Thread_Enable_dispatch () at 
> ../../../../../../gen68360/lib/include/rtems/score/thread.inl:199
> #5  0x84696 in rtems_region_get_segment (id=604045313, 
> size=8, option_set=1, 
> timeout=0, segment=0x177548)
>     at 
> ../../../../../../../rtems-4.5.0-beta3/c/src/exec/rtems/src/re
giongetsegment.c:84
> #6  0x7ef88 in malloc (size=8) at 
> ../../../../../../rtems-4.5.0-beta3/c/src/lib/libc/malloc.c:160
> #7  0x6fcfa in TclpAlloc (nbytes=8) at ./../generic/tclAlloc.c:671
> #8  0x1793a in Tcl_Alloc (size=8) at ./../generic/tclCkalloc.c:813
> 
> 
> It seems that malloc is involved, so I try to get the heap size with:
>  p *((Region_Control 
> *)_Region_Information->local_table[1])->Memory->last
>  
> and get:
>   $4 = {back_flag = 1, front_flag = 2313828, next = 0x17bdf8, 
> previous = 0x3b8f7c}
>   
> Looks like there is still plenty of heap.
> 
> Can anyone point out any flaws or errors in my thinking?
> 
> Thanks!
> 
> Keith
>  
>  
> 
> 
>