[fpc-devel] removed MaxAvail,MemAvail,HeapSize

Konstantin Münning konstantin at muenning.com
Mon May 23 00:56:01 CEST 2005

Jonas Maebe wrote:
> On 22 May 2005, at 20:07, Konstantin Münning wrote:
>>  When you skip the check and allocate always then the program will
>> crash anyway when there is not enough memory.
> No. Either you catch exceptions resulting from a lack of memory and 
> recover, and then you have the same checking as before, except that  the
> check happens atomically (by the OS: you ask for more memory and  if
> there is no more memory, you get an exception).

It seems you are missing a "small" point. Compatibility. With BP7 there
are no exceptions - if you try to allocate more memory than availible
you get a runtime error. This runtime error can't be switched off like
IO-errors. OK, there are the exit procedures, but there is no recover.

The structure of a program is completely different when designing it to
work with exceptions and recovering from these. At least for the
affected parts. All the "old" code needs to be redesigned in a way it
would work ONLY with the new compiler. OK, there are the IFDEF's, but
for most cases it isn't worth the effort.

Last but not least - exception handlers can still be added to deal with
the tiny chance that the problem occurs - no need to change the
"original" code.

> Another possibility to set the global system unit variable 
> ReturnNilIfGrowHeapFails to true, and then you can check after each 
> allocation whether the resulting pointer is nil (if so, not enough 
> memory was available) or not.

That's easier than exceptions but unfortunately also an incompatible way.

I don't think MaxAvail is so bad that everyone must be enforced to stop
using it and is not left to choose by himself. I think most programmers
now would either omit the check expecting the program to fail on low
memory anyway or they would write a replacement function to avoid work
and by this keeping the flaw you are so afraid of. Some will avoid
switching to the new compiler and only a few with impotrtant code which
have not yet done it better would consider doing a major rewrite.

I'm sorry, but I still prefer keeping the compatibility and adding a
warning (with hints) so anyone can do it better. Of course you are right
that this might be a bug source under the specific circumstances but
please don't try to enforce it the community. Otherwise great compiler :-).


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