mono/metadata/sgen-minor-copy-object.h

   1 /*
   2  * sgen-minor-copy-object.h: Copy functions for nursery collections.
   3  *
   4  * Copyright 2001-2003 Ximian, Inc
   5  * Copyright 2003-2010 Novell, Inc.
   6  * Copyright (C) 2012 Xamarin Inc
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Library General Public
  10  * License 2.0 as published by the Free Software Foundation;
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Library General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Library General Public
  18  * License 2.0 along with this library; if not, write to the Free
  19  * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20  */
  21
  22 #define collector_pin_object(obj, queue) sgen_pin_object (obj, queue);
  23 #define COLLECTOR_SERIAL_ALLOC_FOR_PROMOTION alloc_for_promotion
  24
  25 extern long long stat_nursery_copy_object_failed_to_space; /* from sgen-gc.c */
  26
  27 #include "mono/utils/mono-compiler.h"
  28
  29 #include "sgen-copy-object.h"
  30
  31 /*
  32  * This is how the copying happens from the nursery to the old generation.
  33  * We assume that at this time all the pinned objects have been identified and
  34  * marked as such.
  35  * We run scan_object() for each pinned object so that each referenced
  36  * objects if possible are copied. The new gray objects created can have
  37  * scan_object() run on them right away, too.
  38  * Then we run copy_object() for the precisely tracked roots. At this point
  39  * all the roots are either gray or black. We run scan_object() on the gray
  40  * objects until no more gray objects are created.
  41  * At the end of the process we walk again the pinned list and we unmark
  42  * the pinned flag. As we go we also create the list of free space for use
  43  * in the next allocation runs.
  44  *
  45  * We need to remember objects from the old generation that point to the new one
  46  * (or just addresses?).
  47  *
  48  * copy_object could be made into a macro once debugged (use inline for now).
  49  */
  50
  51 static MONO_ALWAYS_INLINE void
  52 SERIAL_COPY_OBJECT (void **obj_slot, SgenGrayQueue *queue)
  53 {
  54         char *forwarded;
  55         char *copy;
  56         char *obj = *obj_slot;
  57
  58         SGEN_ASSERT (9, current_collection_generation == GENERATION_NURSERY, "calling minor-serial-copy from a %d generation collection", current_collection_generation);
  59
  60         HEAVY_STAT (++stat_copy_object_called_nursery);
  61
  62         if (!sgen_ptr_in_nursery (obj)) {
  63                 HEAVY_STAT (++stat_nursery_copy_object_failed_from_space);
  64                 return;
  65         }
  66
  67         SGEN_LOG (9, "Precise copy of %p from %p", obj, obj_slot);
  68
  69         /*
  70          * Before we can copy the object we must make sure that we are
  71          * allowed to, i.e. that the object not pinned, not already
  72          * forwarded or belongs to the nursery To Space.
  73          */
  74
  75         if ((forwarded = SGEN_OBJECT_IS_FORWARDED (obj))) {
  76                 SGEN_ASSERT (9, (*(MonoVTable**)SGEN_LOAD_VTABLE (obj))->gc_descr,  "forwarded object %p has no gc descriptor", forwarded);
  77                 SGEN_LOG (9, " (already forwarded to %p)", forwarded);
  78                 HEAVY_STAT (++stat_nursery_copy_object_failed_forwarded);
  79                 SGEN_UPDATE_REFERENCE (obj_slot, forwarded);
  80                 return;
  81         }
  82         if (G_UNLIKELY (SGEN_OBJECT_IS_PINNED (obj))) {
  83                 SGEN_ASSERT (9, ((MonoVTable*)SGEN_LOAD_VTABLE(obj))->gc_descr, "pinned object %p has no gc descriptor", obj);
  84                 SGEN_LOG (9, " (pinned, no change)");
  85                 HEAVY_STAT (++stat_nursery_copy_object_failed_pinned);
  86                 return;
  87         }
  88
  89 #ifndef SGEN_SIMPLE_NURSERY
  90         if (sgen_nursery_is_to_space (obj)) {
  91                 SGEN_ASSERT (9, ((MonoVTable*)SGEN_LOAD_VTABLE(obj))->gc_descr, "to space object %p has no gc descriptor", obj);
  92                 SGEN_LOG (9, " (tospace, no change)");
  93                 HEAVY_STAT (++stat_nursery_copy_object_failed_to_space);
  94                 return;
  95         }
  96 #endif
  97
  98         HEAVY_STAT (++stat_objects_copied_nursery);
  99
 100         copy = copy_object_no_checks (obj, queue);
 101         SGEN_UPDATE_REFERENCE (obj_slot, copy);
 102 }
 103
 104 /*
 105  * SERIAL_COPY_OBJECT_FROM_OBJ:
 106  *
 107  *   Similar to SERIAL_COPY_OBJECT, but assumes that OBJ_SLOT is part of an object, so it handles global remsets as well.
 108  */
 109 static MONO_ALWAYS_INLINE void
 110 SERIAL_COPY_OBJECT_FROM_OBJ (void **obj_slot, SgenGrayQueue *queue)
 111 {
 112         char *forwarded;
 113         char *obj = *obj_slot;
 114         void *copy;
 115
 116         SGEN_ASSERT (9, current_collection_generation == GENERATION_NURSERY, "calling minor-serial-copy-from-obj from a %d generation collection", current_collection_generation);
 117
 118         HEAVY_STAT (++stat_copy_object_called_nursery);
 119
 120         if (!sgen_ptr_in_nursery (obj)) {
 121                 HEAVY_STAT (++stat_nursery_copy_object_failed_from_space);
 122                 return;
 123         }
 124
 125         SGEN_LOG (9, "Precise copy of %p from %p", obj, obj_slot);
 126
 127         /*
 128          * Before we can copy the object we must make sure that we are
 129          * allowed to, i.e. that the object not pinned, not already
 130          * forwarded or belongs to the nursery To Space.
 131          */
 132
 133         if ((forwarded = SGEN_OBJECT_IS_FORWARDED (obj))) {
 134                 SGEN_ASSERT (9, (*(MonoVTable**)SGEN_LOAD_VTABLE (obj))->gc_descr,  "forwarded object %p has no gc descriptor", forwarded);
 135                 SGEN_LOG (9, " (already forwarded to %p)", forwarded);
 136                 HEAVY_STAT (++stat_nursery_copy_object_failed_forwarded);
 137                 SGEN_UPDATE_REFERENCE (obj_slot, forwarded);
 138 #ifndef SGEN_SIMPLE_NURSERY
 139                 if (G_UNLIKELY (sgen_ptr_in_nursery (forwarded) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (forwarded)))
 140                         sgen_add_to_global_remset (obj_slot, forwarded);
 141 #endif
 142                 return;
 143         }
 144         if (G_UNLIKELY (SGEN_OBJECT_IS_PINNED (obj))) {
 145                 SGEN_ASSERT (9, ((MonoVTable*)SGEN_LOAD_VTABLE(obj))->gc_descr, "pinned object %p has no gc descriptor", obj);
 146                 SGEN_LOG (9, " (pinned, no change)");
 147                 HEAVY_STAT (++stat_nursery_copy_object_failed_pinned);
 148                 if (!sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (obj))
 149                         sgen_add_to_global_remset (obj_slot, obj);
 150                 return;
 151         }
 152
 153 #ifndef SGEN_SIMPLE_NURSERY
 154         if (sgen_nursery_is_to_space (obj)) {
 155                 SGEN_ASSERT (9, ((MonoVTable*)SGEN_LOAD_VTABLE(obj))->gc_descr, "to space object %p has no gc descriptor", obj);
 156                 SGEN_LOG (9, " (tospace, no change)");
 157                 HEAVY_STAT (++stat_nursery_copy_object_failed_to_space);
 158
 159                 /*
 160                  * FIXME:
 161                  *
 162                  * The card table scanning code sometimes clears cards
 163                  * that have just been set for a global remset.  In
 164                  * the split nursery the following situation can
 165                  * occur:
 166                  *
 167                  * Let's say object A starts in card C but continues
 168                  * into C+1.  Within A, at offset O there's a
 169                  * reference to a new nursery object X.  A+O is in
 170                  * card C+1.  Now card C is scanned, and as part of
 171                  * it, object A.  The reference at A+O is processed by
 172                  * copying X into nursery to-space at Y.  Since it's
 173                  * still in the nursery, a global remset must be added
 174                  * for A+O, so card C+1 is marked.  Now, however, card
 175                  * C+1 is scanned, which means that it's cleared
 176                  * first.  This wouldn't be terribly bad if reference
 177                  * A+O were re-scanned and the global remset re-added,
 178                  * but since the reference points to to-space, that
 179                  * doesn't happen, and C+1 remains cleared: the remset
 180                  * is lost.
 181                  *
 182                  * There's at least two ways to fix this.  The easy
 183                  * one is to re-add the remset on the re-scan.  This
 184                  * is that - the following two lines of code.
 185                  *
 186                  * The proper solution appears to be to first make a
 187                  * copy of the cards before scanning a block, then to
 188                  * clear all the cards and scan from the copy, so no
 189                  * remsets will be overwritten.  Scanning objects at
 190                  * most once would be the icing on the cake.
 191                  */
 192                 if (!sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (obj))
 193                         sgen_add_to_global_remset (obj_slot, obj);
 194
 195                 return;
 196         }
 197 #endif
 198
 199         HEAVY_STAT (++stat_objects_copied_nursery);
 200
 201         copy = copy_object_no_checks (obj, queue);
 202         SGEN_UPDATE_REFERENCE (obj_slot, copy);
 203 #ifndef SGEN_SIMPLE_NURSERY
 204         if (G_UNLIKELY (sgen_ptr_in_nursery (copy) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (copy)))
 205                 sgen_add_to_global_remset (obj_slot, copy);
 206 #else
 207         /* copy_object_no_checks () can return obj on OOM */
 208         if (G_UNLIKELY (obj == copy)) {
 209                 if (G_UNLIKELY (sgen_ptr_in_nursery (copy) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (copy)))
 210                         sgen_add_to_global_remset (obj_slot, copy);
 211         }
 212 #endif
 213 }
 214
 215 #define FILL_MINOR_COLLECTOR_COPY_OBJECT(collector)     do {                    \
 216                 (collector)->serial_ops.copy_or_mark_object = SERIAL_COPY_OBJECT;                       \
 217         } while (0)