Re: Crash when calling C from a finalizer

[Gaspard Bucher <gaspard@...>]

On Thu, Dec 29, 2011 at 5:38 PM, Roberto Ierusalimschy
<roberto@inf.puc-rio.br> wrote:
>
> > I think it would be very valuable to have a comment on finalizers and what
> > can be done in these in the reference manual. I lost a day's work
> > struggling with gdb to discover that calling any method from "C" from a
> > finalizer is a bad idea (crash).
> >
> > [...]
> >
> > *29 – Managing Resources*
> > Life is not always that easy. [...]. This function can then release any
> > resource associated with that userdatum *but it should not call a C
> > function from Lua*.
> >
> >
> > Or maybe the rule is slightly more complex. In my case, the crash happens
> > with:
> >
> > Lua GC ---> Foobar::finalizer (custom C++ finalizer) --> pcall --> call C
> > function
>
> There is no such restriction. You should be able to do whatever you want
> from a finalizer.
>
> -- Roberto
>

Hi Roberto, thanks for the feedback. This means that my problem is
even more strange. The crash happens whatever C function I call. Here
is the gdb dump:

#0  0x00000001018637c0 in ?? ()
Cannot access memory at address 0x1018637c0
#1  0x000000010003005e in luaV_execute (L=0x1005013c0, nexeccalls=4)
at lvm.c:590
#2  0x0000000100010b60 in luaD_call (L=0x1005013c0, func=0x1005015e0,
nResults=0) at ldo.c:377
#3  0x0000000100003847 in f_call (L=0x1005013c0, ud=0x7fff5fbff020) at
lapi.c:800
#4  0x000000010000f8a2 in luaD_rawrunprotected (L=0x1005013c0,
f=0x100003810 <f_call>, ud=0x7fff5fbff020) at ldo.c:116
#5  0x000000010001100e in luaD_pcall (L=0x1005013c0, func=0x100003810
<f_call>, u=0x7fff5fbff020, old_top=32, ef=0) at ldo.c:463
#6  0x000000010000391b in lua_pcall (L=0x1005013c0, nargs=1,
nresults=0, errfunc=0) at lapi.c:821
#7  0x00000001000f894c in lk::Finalizer::finalize (this=0x1005012b0)
at Finalizer.h:53
#8  0x00000001000f843b in Finalizer_destructor (L=0x1001009d0) at
Finalizer_core.cpp:39
#9  0x00000001000107fc in luaD_precall (L=0x1001009d0,
func=0x100803810, nresults=0) at ldo.c:319
#10 0x0000000100010b46 in luaD_call (L=0x1001009d0, func=0x100803810,
nResults=0) at ldo.c:376
#11 0x0000000100013f1f in GCTM (L=0x1001009d0) at lgc.c:467
#12 0x0000000100013f5a in luaC_callGCTM (L=0x1001009d0) at lgc.c:479
#13 0x000000010002260c in callallgcTM (L=0x1001009d0, ud=0x0) at lstate.c:195
#14 0x000000010000f8a2 in luaD_rawrunprotected (L=0x1001009d0,
f=0x1000225f0 <callallgcTM>, ud=0x0) at ldo.c:116
#15 0x00000001000226e5 in lua_close (L=0x1001009d0) at lstate.c:209
#16 0x000000010002b1f1 in main (argc=2, argv=0x7fff5fbff3a0) at lua.c:389

Not calling a C function works fine so I guessed this was the problem...

                                                               Gaspard