[fpc-devel] Boehm garbage collector for freepascal

Marco van de Voort marcov at stack.nl
Mon Nov 15 14:50:51 CET 2010

In our previous episode, Thaddy said:
> You can find boehm garbage collector bindings for freepascal, incl. 
> replacement memory manager at
> http://freepascal.thaddy.co.uk/fpc_boehm_gc.zip
> For win32 a prebuild dll is included
> For other platforms you need to build the gc library from source (included)
> Please test, I am especially curious how it behaves on other platforms.
> freepascal.thaddy.co.uk/fpc_boehm_gc.zip
> I Also have a question:
> (After you played with the example and read the docs)

Oh. Am I supposed to do that? :-)

(I just collect info about this subject because it is a recurring white
elephant. Regularly there is talk about it, but nobody has seen a working
implementation, and nobody knows if proof of implementation on  C++
really does translate to Delphi. (like the finalization bit below)

 I myself are not interested in GC in my current job (but was
in my previous webapp job)

> Suppose I want a GC version of freepascal, would it be enough to patch 
> TObject.InitInstance/TObject.FreeInstance for finalization and adapt 
> heap.inc and do a make clean/make all?

I was thinking that one would install a heapmanager with a freemem that does
nothing.  Unfortunately the prototype can't zero the pointer (like
freeandnil does)

All allocations are eventually getmem/freemem, so redirecting getmem to the
gc's prefered memory allocation and making freemem a no-op would be enough I

> Tobject descendants may require finalization before the garbage 
> collector cleans them, hence my question.

Hmm, yes. That means indeed the GC must be able to call a callback on a
block that must be freed, and some call to finalize must be made there. But
will you have enough context to do so?

Or will we simply not finalize and let the GC collect ansistrings and the
like too? I always assumed that.

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