[fpc-pascal] replacement of MARK and RELEASE function in free pascal

[Sven Barth]

On 19.06.2014 16:37, johanns at nacs.net wrote:
> On Thu, Jun 19, 2014 at 03:28:42PM +0200, Sven Barth wrote:
>> On 19.06.2014 13:29, Karoly Balogh (Charlie/SGR) wrote:
>>> So either you use mypointer:=GetMem(size); or GetMem(mypointer, size);
>>> both are valid. If you need to allocate heap space for a record,
>>> use New/Dispose, or GetMem(myptr, sizeof(Tmyrecord));
>>
>> I wouldn't use GetMem() in case of record pointers just in case a
>> managed type happens to be in there. Unlike GetMem() New() does
>> initialize those fields correctly. Alternatively one should use
>> Initialize(myptr^) after the call to GetMem().
>>
>
> I seem to remember being warned in the old days of Turbo Pascal not mix
> use of getmem()/freemem() and new()/dispose() within a program, due to
> differences in the memory allocation strategies.  Are there still any
> compatibility or efficiency/performance issues with alternating between
> these two families, or can the most simple or appropriate call be used
> interchangeably?  In other words, now that objects are so much more
> prevalent in Pascal code, should getmem() and freemem() be avoided?

I think even back then it was meant that you shouldn't freemem() memory 
allocated with new() and vise versa.
Nevertheless in FPC you are free to use whatever you deem suitable (and 
afterall there are situations when you *can't* use a new(), namely on 
untyped pointers) the only thing you should keep in mind is that you 
should dispose() memory allocated by new() and freemem() memory 
allocated getmem(), but no mixing on the same pointer. It *might* work 
(and indeed if the type pointed to doesn't contain managed types it will 
in fact be the same), but we do not guarantee anywhere that it will stay 
that way.

Regards,
Sven