[fpc-devel] Why/how does the compiler have a non-trivial number ofmemory leaks after over two decades of development?

[J. Gareth Moreton]

On Mon 30/07/18 01:58 , Ben Grasset 
operator97 at gmail.com sent:
> I was even able to successfully actually 
fix some of the leaks, but others
> boiled down to a "node" being created as 
a local variable in the middle of
> some 1000+ line method, getting assigned 
to the "left" or "right" property
> of some other globally visible node, and 
then never being freed.
> To add to that, some of then actually 
*could not* be freed even when I
> tried to do so without raising an 
untraceable access violation later in the
> compilation process, also, which means 
the compiler is basically knowingly
> relying on undebuggable undefined 
behaviour in multiple places that could
> easily be affected or altered by 
anything else anywhere else in the
> codebase at any time. 
> The way-too-short, highly undescriptive 
naming of variables doesn't
> exactly help, either! "hp" and "p" are 
not good variable names. They really
> aren't! 
> 
> Overall, I'm not trying to put blame on 
anyone in particular here, but as
> someone who loves using FPC and would 
like to see it continue to grow, it
> would be nice if we could collectively 
address some of these basic,
> fundamental issues (which I'd be happy 
to help with myself, of course.) 
>

I too love Free Pascal and seek to improve 
it. If you've found a fix, by all means 
submit it as a patch in the bug tracker.

I've noticed that the compiler doesn't use 
try...finally blocks to help with freeing 
blocks. I'm not sure why this is the case, 
but might be speed related.

More complex refactoring might require 
deeper planning and approval from Florian. 
For example, the node construction relies 
a lot on global variables (especially 
current_procinfo) that could possibly use 
some improvement.

I think a big issue with refactoring is 
the amount of testing required because of 
the numerous target platforms.

Don't be disheartened though. With enough 
eyes, all bugs are shallow!

Gareth aka. Kit