diff options
Diffstat (limited to 'mallocx.c')
| -rw-r--r-- | mallocx.c | 38 |
1 files changed, 32 insertions, 6 deletions
@@ -106,13 +106,39 @@ GC_API void * GC_CALL GC_realloc(void * p, size_t lb) if (sz > MAXOBJBYTES) { /* Round it up to the next whole heap block */ - word descr; + word descr = GC_obj_kinds[obj_kind].ok_descriptor; + + sz = (sz + HBLKSIZE-1) & ~HBLKMASK; + if (GC_obj_kinds[obj_kind].ok_relocate_descr) + descr += sz; + /* GC_realloc might be changing the block size while */ + /* GC_reclaim_block or GC_clear_hdr_marks is examining it. */ + /* The change to the size field is benign, in that GC_reclaim */ + /* (and GC_clear_hdr_marks) would work correctly with either */ + /* value, since we are not changing the number of objects in */ + /* the block. But seeing a half-updated value (though unlikely */ + /* to occur in practice) could be probably bad. */ + /* Using unordered atomic accesses on the size and hb_descr */ + /* fields would solve the issue. (The alternate solution might */ + /* be to initially overallocate large objects, so we do not */ + /* have to adjust the size in GC_realloc, if they still fit. */ + /* But that is probably more expensive, since we may end up */ + /* scanning a bunch of zeros during GC.) */ +# ifdef AO_HAVE_store + GC_STATIC_ASSERT(sizeof(hhdr->hb_sz) == sizeof(AO_t)); + AO_store((volatile AO_t *)&hhdr->hb_sz, (AO_t)sz); + AO_store((volatile AO_t *)&hhdr->hb_descr, (AO_t)descr); +# else + { + DCL_LOCK_STATE; + + LOCK(); + hhdr -> hb_sz = sz; + hhdr -> hb_descr = descr; + UNLOCK(); + } +# endif - sz = (sz+HBLKSIZE-1) & (~HBLKMASK); - hhdr -> hb_sz = sz; - descr = GC_obj_kinds[obj_kind].ok_descriptor; - if (GC_obj_kinds[obj_kind].ok_relocate_descr) descr += sz; - hhdr -> hb_descr = descr; # ifdef MARK_BIT_PER_OBJ GC_ASSERT(hhdr -> hb_inv_sz == LARGE_INV_SZ); # endif |