[Octave-bug-tracker] [bug #51088] double free at Octave exit

[Olaf Till]

Follow-up Comment #4, bug #51088 (project octave):

The second half of the changeset is not necessary to fix the bug as it was
currently triggered. But I thought a similar bug could occur if this change
isn't made, too.

To explain the second half:

To your question: The destructor of the symbol_table (being empty, but
automatically calling the destructors of the contained objects), _is_ called
by deleting with the copy 'inst' of 'p->second'. The '...->second' entries in
'all_instances' are zeroed before triggering the destructor call to avoid that
the side effects of the destructor may try to trigger a destructor of a
specific symbol table a second time (over 'all_instances').

This deleting with a pointer copy, _after_ zeroing the original pointer, is
the same as was done already before my patch in symtab.cc,
symbol_table::cleanup(), to avoid that side effects call destructors of
already destroyed symbol_tables. Here, in symbtab.h,
symbol_table::erase_scope(), my change is only a precaution against the
possibility that the side effects could try to destroy (over 'all_instances')
the _same_ symbol table as we currently already are destroying. Or can someone
exclude that this happens? I'd rather be at the safe side.


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