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Prepare SMOBs for new finalization API

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* libguile/atomics-internal.h (scm_atomic_set_bits): New routine.
* libguile/smob.c (scm_i_finalize_smob): Use atomics to clear the first
word instead of the GC alloc lock.
(finalize_smob): Implement as shim.
This commit is contained in:
Andy Wingo 2025-05-02 15:06:41 +02:00
parent 1a3f427d4e
commit 5e97645b81
3 changed files with 37 additions and 28 deletions
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16
libguile/atomics-internal.h
View file

@ -1,7 +1,7 @@
#ifndef SCM_ATOMICS_INTERNAL_H
#define SCM_ATOMICS_INTERNAL_H
/* Copyright 2016,2018-2019
/* Copyright 2016,2018-2019,2025
Free Software Foundation, Inc.
This file is part of Guile.
@ -58,6 +58,12 @@ scm_atomic_ref_pointer (void **loc)
return (void *) atomic_load (a_loc);
}
static inline void
scm_atomic_set_bits (scm_t_bits *loc, scm_t_bits val)
{
atomic_uintptr_t *a_loc = (atomic_uintptr_t *) loc;
atomic_store (a_loc, val);
}
static inline void
scm_atomic_set_scm (SCM *loc, SCM val)
{
atomic_uintptr_t *a_loc = (atomic_uintptr_t *) loc;
@ -136,6 +142,14 @@ scm_atomic_ref_pointer (void **loc)
return ret;
}
static inline void
scm_atomic_set_bits (scm_t_bits *loc, scm_t_bits val)
{
scm_i_pthread_mutex_lock (&atomics_lock);
*loc = val;
scm_i_pthread_mutex_unlock (&atomics_lock);
}
static inline void
scm_atomic_set_scm (SCM *loc, SCM val)
{

45
libguile/smob.c
View file

@ -1,4 +1,4 @@
/* Copyright 1995-1996,1998-2001,2003-2004,2006,2009-2013,2015,2018
/* Copyright 1995-1996,1998-2001,2003-2004,2006,2009-2013,2015,2018,2025
Free Software Foundation, Inc.
This file is part of Guile.
@ -29,6 +29,7 @@
#include <stdlib.h>
#include "async.h"
#include "atomics-internal.h"
#include "bdw-gc.h"
#include "finalizers.h"
#include "goops.h"
@ -375,45 +376,37 @@ scm_gc_mark (SCM o)
}
static void*
clear_smobnum (void *ptr)
/* Finalize SMOB by calling its SMOB type's free function, if any. */
void
scm_i_finalize_smob (struct scm_thread *thread, SCM smob)
{
SCM smob;
scm_t_bits smobnum;
scm_t_bits *first_word_loc = SCM_UNPACK_POINTER (smob);
scm_t_bits first_word = *first_word_loc;
scm_t_bits smobnum = SCM_TC2SMOBNUM (first_word & SCM_SMOB_TYPE_MASK);
smob = SCM_PACK_POINTER (ptr);
smobnum = SCM_SMOBNUM (smob);
/* Frob the object's type in place, re-setting it to be the "finalized
smob" type. This will prevent other routines from accessing its
internals in a way that assumes that the smob data is valid. This
is notably the case for SMOB's own "mark" procedure, if any; as the
finalizer runs without the alloc lock, it's possible for a GC to
finalizer is invoked by the mutator, it's possible for a GC to
occur while it's running, in which case the object is alive and yet
its data is invalid. */
SCM_SET_SMOB_DATA_0 (smob, SCM_SMOB_DATA_0 (smob) & ~(scm_t_bits) 0xff00);
scm_t_bits finalized_word = first_word & ~(scm_t_bits) 0xff00;
scm_atomic_set_bits (first_word_loc, finalized_word);
return (void *) smobnum;
#if 0
printf ("finalizing SMOB %p (smobnum: %u)\n", first_word_loc, smobnum);
#endif
size_t (* free_smob) (SCM) = scm_smobs[smobnum].free;
if (free_smob)
free_smob (smob);
}
/* Finalize SMOB by calling its SMOB type's free function, if any. */
static void
finalize_smob (void *ptr, void *data)
{
SCM smob;
scm_t_bits smobnum;
size_t (* free_smob) (SCM);
smob = SCM_PACK_POINTER (ptr);
smobnum = (scm_t_bits) GC_call_with_alloc_lock (clear_smobnum, ptr);
#if 0
printf ("finalizing SMOB %p (smobnum: %u)\n", ptr, smobnum);
#endif
free_smob = scm_smobs[smobnum].free;
if (free_smob)
free_smob (smob);
return scm_i_finalize_smob (SCM_I_CURRENT_THREAD, PTR2SCM (ptr));
}
/* Return a SMOB with typecode TC. The SMOB type corresponding to TC may

4
libguile/smob.h
View file

@ -1,7 +1,7 @@
#ifndef SCM_SMOB_H
#define SCM_SMOB_H
/* Copyright 1995-1996,1998-2001,2004,2006,2009-2012,2015,2018
/* Copyright 1995-1996,1998-2001,2004,2006,2009-2012,2015,2018,2025
Free Software Foundation, Inc.
This file is part of Guile.
@ -256,6 +256,8 @@ SCM_API void scm_assert_smob_type (scm_t_bits tag, SCM val);
SCM_API SCM scm_make_smob (scm_t_bits tc);
SCM_INTERNAL void scm_i_finalize_smob (struct scm_thread *thread, SCM obj);
SCM_API void scm_smob_prehistory (void);
#endif /* SCM_SMOB_H */