[Python-Dev] tp_dealloc

[Amaury Forgeot d'Arc]

2010/6/1  <smarv at gmx.net>:
> Sorry, I wrote tp_alloc in last post, it should be always tp_dealloc:
>
> My tp_dealloc method (of non-subtypable type) calls the freeMem-method
> of a memory manager (this manager was also used for the corresponding allocation).
> This freeMem-method deallocates and modifies the memory,
> which is a valid action, because after free, the memory-manager
> has ownership of the freed memory.
> Several memory managers do this (for example the Memory Manager in
> Delphi during debug mode, in order to track invalid memory access after free).
>
> The python31.dll calls tp_dealloc and later (after return of tp_dealloc)
> the python31.dll is still awaiting valid content in the deallocated memory.
> I don't know where this happens, I'm not a developer of CPython,
> but at this point the python31.dll causes an access violation.
> IMO the python31.dll assumes that freeMem never modifies the memory
> (pyobject header), this is valid for many memory managers, but not for all.
> And from my perspective, this assumption a bug, which can cause access violations in many applications (for example, applications which use the
> PythonForDelphi-package; PyScripter is one of them, but also many others)
>
> Please, could some CPython-developer take a look, thank you!

CPython does not access memory after the call to tp_dealloc.
There is even a mode (--without-pymalloc) where tp_dealloc calls
free() at the end,
and would cause crashes if the memory was read afterwards.

This said, there may be a bug somewhere, but what do you want us to look at?
Do you have a case that we could reproduce and investigate?

-- 
Amaury Forgeot d'Arc