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bug#58732: installer: finalizers & device destroy segfault
From: |
Mathieu Othacehe |
Subject: |
bug#58732: installer: finalizers & device destroy segfault |
Date: |
Thu, 03 Nov 2022 12:09:16 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) |
Hey,
Thanks for your help :)
> 1. Bindings create wrappers for C pointers—e.g., with
> ‘pointer->device’. If several C functions return a pointer P, you
> must make sure to return always the same wrapper and not create a
> new one.
Agreed.
>
> ‘pointer->device!’ attempts to do that but I think it’s bogus: it
> uses a weak-value hash table, where the value is the wrapper. So
> if the wrapper disappears before the underlying C object, then the
> pointer is called and bad things ensue.
I'm not sure to understand how could the wrapper disappear before the
underlying C object? We are only exposing <device> records to the
Guile-Parted users so my assumption is that when <device> goes out of
scope, the pointer it wraps can be freed, but I'm maybe missing
something?
> ‘define-wrapped-pointer-type’ in Guile is meant to help with these
> things (info "(guile) Void Pointers and Byte Access"). We can’t
> use it directly here because we’re using bytestructures and all
> that.
Turns out, the "wrap" procedure defined in define-wrapped-pointer-type
is a clone of pointer->device! except that it doesn't set a
finalizer.
Regarding object lifetime, I wrote a small memo in 2019 here:
https://issues.guix.gnu.org/36402#11.
We have three weak hash tables in Guile-Parted:
%devices: To make sure that we do not set multiple finalizers on the
same pointers.
%disk-devices: So that a device always outlives its disks.
%partition-disks: So that a disk always outlives its partitions.
This means that as far as I can tell we are OK regarding your second
point about "aggregation relations".
Mathieu
- bug#58732: installer: finalizers & device destroy segfault, Ludovic Courtès, 2022/11/02
- bug#58732: installer: finalizers & device destroy segfault,
Mathieu Othacehe <=
- bug#58732: installer: finalizers & device destroy segfault, Ludovic Courtès, 2022/11/03
- bug#58732: installer: finalizers & device destroy segfault, Mathieu Othacehe, 2022/11/06
- bug#58732: installer: finalizers & device destroy segfault, Ludovic Courtès, 2022/11/07
- bug#58732: installer: finalizers & device destroy segfault, Mathieu Othacehe, 2022/11/07
- bug#58732: installer: finalizers & device destroy segfault, Mathieu Othacehe, 2022/11/09
- bug#58732: installer: finalizers & device destroy segfault, Ludovic Courtès, 2022/11/10
- bug#58732: installer: finalizers & device destroy segfault, Mathieu Othacehe, 2022/11/10