[fpc-devel] removed MaxAvail,MemAvail,HeapSize

[Florian Klaempfl]

Konstantin Münning wrote:
>>And in all cases, the program will still crash occasionally because  it
>>runs out of memory in certain cases, because the check and the 
>>allocation do not happen atomically. You can't put something into the 
>>standard Run Time Library which works "most of the time, except under 
>>heavy load". Imagine reading the docs and encountering that comment, 
>>you'd immediately start wondering how many more procedures there are 
>>which work "most of the time".
> 
> 
> Most programs work most of the time except under heavy load. That's not
> a good argument. Most small (C) programs don't do any memory

Pascal is not C ;)

> availability checks at all. Look at most of the command line tools on
> any OS ;-). Of course I would like to have any code behave perfect under
> any condition but it has always been a tradeoff between effort
> (=expense) and impact. But when there is no memory left and you need
> some you can't behave perfect. Please let it be the programmers choice
> what to do and how to handle this. A compiler should be providing the
> means, not taking them away. Anybody writing a program knows that there
> may be flaws. A warning (with an advice how to make it better) should
> still be the best for this.
> 
> By the way, I've found the following code in compiler/cclasses.pas when
> I searched for the whereabouts of maxavail/memavail and there were some
> more like this in the sources:
> 
> {$ifdef HASGETHEAPSTATUS}
>         status:=GetFPCHeapStatus;
>         startmem:=status.CurrHeapUsed;
> {$else HASGETHEAPSTATUS}
>         startmem:=memavail;
> {$endif HASGETHEAPSTATUS}
> 
> I'm not sure if I understand it right as GetHeapStatus is not documented
> well (I've found no reference for the meaning of the fields of the
> returned record) but it seems that someone repaced here memavail with
> another code which does about the same and has therefore the same flaw.

It has been moved to heap status which contains more info which also reliable on
multitasking systems.

> 
> I would hapily contribute the code for a better MemAvail/MaxAvail
> function if that's the problem. I would like to be able to use the
> latest compiler which now I definitely can't 

See below.

> as I must have the BP7
> compatibility which is very good in 1.0.10.

What about Mark and Release when talking about heap management ;)?

A compromise would be a tpascal unit which is loaded only in -So mode.