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

   1 /**
   2  * \file
   3  * Copy functions for nursery collections.
   4  *
   5  * Copyright 2001-2003 Ximian, Inc
   6  * Copyright 2003-2010 Novell, Inc.
   7  * Copyright (C) 2012 Xamarin Inc
   8  *
   9  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
  10  */
  11
  12 #undef SERIAL_COPY_OBJECT
  13 #undef SERIAL_COPY_OBJECT_FROM_OBJ
  14
  15 #if defined(SGEN_SIMPLE_NURSERY)
  16
  17 #ifdef SGEN_SIMPLE_PAR_NURSERY
  18
  19 #ifdef SGEN_CONCURRENT_MAJOR
  20 #define SERIAL_COPY_OBJECT simple_par_nursery_with_concurrent_major_copy_object
  21 #define SERIAL_COPY_OBJECT_FROM_OBJ simple_par_nursery_with_concurrent_major_copy_object_from_obj
  22 #else
  23 #define SERIAL_COPY_OBJECT simple_par_nursery_copy_object
  24 #define SERIAL_COPY_OBJECT_FROM_OBJ simple_par_nursery_copy_object_from_obj
  25 #endif
  26
  27 #else
  28
  29 #ifdef SGEN_CONCURRENT_MAJOR
  30 #define SERIAL_COPY_OBJECT simple_nursery_serial_with_concurrent_major_copy_object
  31 #define SERIAL_COPY_OBJECT_FROM_OBJ simple_nursery_serial_with_concurrent_major_copy_object_from_obj
  32 #else
  33 #define SERIAL_COPY_OBJECT simple_nursery_serial_copy_object
  34 #define SERIAL_COPY_OBJECT_FROM_OBJ simple_nursery_serial_copy_object_from_obj
  35 #endif
  36
  37 #endif
  38
  39 #elif defined (SGEN_SPLIT_NURSERY)
  40
  41 #ifdef SGEN_CONCURRENT_MAJOR
  42 #define SERIAL_COPY_OBJECT split_nursery_serial_with_concurrent_major_copy_object
  43 #define SERIAL_COPY_OBJECT_FROM_OBJ split_nursery_serial_with_concurrent_major_copy_object_from_obj
  44 #else
  45 #define SERIAL_COPY_OBJECT split_nursery_serial_copy_object
  46 #define SERIAL_COPY_OBJECT_FROM_OBJ split_nursery_serial_copy_object_from_obj
  47 #endif
  48
  49 #else
  50 #error "No nursery configuration specified"
  51 #endif
  52
  53
  54 extern guint64 stat_nursery_copy_object_failed_to_space; /* from sgen-gc.c */
  55
  56 /*
  57  * This is how the copying happens from the nursery to the old generation.
  58  * We assume that at this time all the pinned objects have been identified and
  59  * marked as such.
  60  * We run scan_object() for each pinned object so that each referenced
  61  * objects if possible are copied. The new gray objects created can have
  62  * scan_object() run on them right away, too.
  63  * Then we run copy_object() for the precisely tracked roots. At this point
  64  * all the roots are either gray or black. We run scan_object() on the gray
  65  * objects until no more gray objects are created.
  66  * At the end of the process we walk again the pinned list and we unmark
  67  * the pinned flag. As we go we also create the list of free space for use
  68  * in the next allocation runs.
  69  *
  70  * We need to remember objects from the old generation that point to the new one
  71  * (or just addresses?).
  72  *
  73  * copy_object could be made into a macro once debugged (use inline for now).
  74  */
  75
  76 static MONO_ALWAYS_INLINE void
  77 SERIAL_COPY_OBJECT (GCObject **obj_slot, SgenGrayQueue *queue)
  78 {
  79         GCObject *forwarded;
  80         GCObject *copy;
  81         GCObject *obj = *obj_slot;
  82
  83         SGEN_ASSERT (9, sgen_current_collection_generation == GENERATION_NURSERY, "calling minor-serial-copy from a %d generation collection", sgen_current_collection_generation);
  84
  85         HEAVY_STAT (++stat_copy_object_called_nursery);
  86
  87         if (!sgen_ptr_in_nursery (obj)) {
  88                 HEAVY_STAT (++stat_nursery_copy_object_failed_from_space);
  89                 return;
  90         }
  91
  92         SGEN_LOG (9, "Precise copy of %p from %p", obj, obj_slot);
  93
  94         /*
  95          * Before we can copy the object we must make sure that we are
  96          * allowed to, i.e. that the object not pinned, not already
  97          * forwarded or belongs to the nursery To Space.
  98          */
  99
 100         if ((forwarded = SGEN_OBJECT_IS_FORWARDED (obj))) {
 101                 SGEN_ASSERT (9, sgen_obj_get_descriptor (forwarded),  "forwarded object %p has no gc descriptor", forwarded);
 102                 SGEN_LOG (9, " (already forwarded to %p)", forwarded);
 103                 HEAVY_STAT (++stat_nursery_copy_object_failed_forwarded);
 104                 SGEN_UPDATE_REFERENCE (obj_slot, forwarded);
 105                 return;
 106         }
 107         if (G_UNLIKELY (SGEN_OBJECT_IS_PINNED (obj))) {
 108                 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "pinned object %p has no gc descriptor", obj);
 109                 SGEN_LOG (9, " (pinned, no change)");
 110                 HEAVY_STAT (++stat_nursery_copy_object_failed_pinned);
 111                 return;
 112         }
 113
 114 #ifndef SGEN_SIMPLE_NURSERY
 115         if (sgen_nursery_is_to_space (obj)) {
 116                 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "to space object %p has no gc descriptor", obj);
 117                 SGEN_LOG (9, " (tospace, no change)");
 118                 HEAVY_STAT (++stat_nursery_copy_object_failed_to_space);
 119                 return;
 120         }
 121 #endif
 122
 123         HEAVY_STAT (++stat_objects_copied_nursery);
 124
 125 #ifdef SGEN_SIMPLE_PAR_NURSERY
 126         copy = copy_object_no_checks_par (obj, queue);
 127 #else
 128         copy = copy_object_no_checks (obj, queue);
 129 #endif
 130         SGEN_UPDATE_REFERENCE (obj_slot, copy);
 131 }
 132
 133 /*
 134  * SERIAL_COPY_OBJECT_FROM_OBJ:
 135  *
 136  *   Similar to SERIAL_COPY_OBJECT, but assumes that OBJ_SLOT is part of an object, so it handles global remsets as well.
 137  */
 138 static MONO_ALWAYS_INLINE void
 139 SERIAL_COPY_OBJECT_FROM_OBJ (GCObject **obj_slot, SgenGrayQueue *queue)
 140 {
 141         GCObject *forwarded;
 142         GCObject *obj = *obj_slot;
 143         GCObject *copy;
 144
 145         SGEN_ASSERT (9, sgen_current_collection_generation == GENERATION_NURSERY, "calling minor-serial-copy-from-obj from a %d generation collection", sgen_current_collection_generation);
 146
 147         HEAVY_STAT (++stat_copy_object_called_nursery);
 148
 149         if (!sgen_ptr_in_nursery (obj)) {
 150                 HEAVY_STAT (++stat_nursery_copy_object_failed_from_space);
 151                 return;
 152         }
 153
 154         SGEN_LOG (9, "Precise copy of %p from %p", obj, obj_slot);
 155
 156         /*
 157          * Before we can copy the object we must make sure that we are
 158          * allowed to, i.e. that the object not pinned, not already
 159          * forwarded or belongs to the nursery To Space.
 160          */
 161
 162         if ((forwarded = SGEN_OBJECT_IS_FORWARDED (obj))) {
 163                 SGEN_ASSERT (9, sgen_obj_get_descriptor (forwarded),  "forwarded object %p has no gc descriptor", forwarded);
 164                 SGEN_LOG (9, " (already forwarded to %p)", forwarded);
 165                 HEAVY_STAT (++stat_nursery_copy_object_failed_forwarded);
 166 #ifdef SGEN_CONCURRENT_MAJOR
 167                 /* See comment on STORE_STORE_FENCE below. */
 168                 STORE_STORE_FENCE;
 169 #endif
 170                 SGEN_UPDATE_REFERENCE (obj_slot, forwarded);
 171 #ifndef SGEN_SIMPLE_NURSERY
 172                 if (G_UNLIKELY (sgen_ptr_in_nursery (forwarded) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (forwarded)))
 173                         sgen_add_to_global_remset (obj_slot, forwarded);
 174 #endif
 175                 return;
 176         }
 177         if (G_UNLIKELY (SGEN_OBJECT_IS_PINNED (obj))) {
 178                 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "pinned object %p has no gc descriptor", obj);
 179                 SGEN_LOG (9, " (pinned, no change)");
 180                 HEAVY_STAT (++stat_nursery_copy_object_failed_pinned);
 181                 if (!sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (obj))
 182                         sgen_add_to_global_remset (obj_slot, obj);
 183                 return;
 184         }
 185
 186 #ifndef SGEN_SIMPLE_NURSERY
 187         if (sgen_nursery_is_to_space (obj)) {
 188                 /* FIXME: all of these could just use `sgen_obj_get_descriptor_safe()` */
 189                 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "to space object %p has no gc descriptor", obj);
 190                 SGEN_LOG (9, " (tospace, no change)");
 191                 HEAVY_STAT (++stat_nursery_copy_object_failed_to_space);
 192
 193                 /*
 194                  * FIXME:
 195                  *
 196                  * The card table scanning code sometimes clears cards
 197                  * that have just been set for a global remset.  In
 198                  * the split nursery the following situation can
 199                  * occur:
 200                  *
 201                  * Let's say object A starts in card C but continues
 202                  * into C+1.  Within A, at offset O there's a
 203                  * reference to a new nursery object X.  A+O is in
 204                  * card C+1.  Now card C is scanned, and as part of
 205                  * it, object A.  The reference at A+O is processed by
 206                  * copying X into nursery to-space at Y.  Since it's
 207                  * still in the nursery, a global remset must be added
 208                  * for A+O, so card C+1 is marked.  Now, however, card
 209                  * C+1 is scanned, which means that it's cleared
 210                  * first.  This wouldn't be terribly bad if reference
 211                  * A+O were re-scanned and the global remset re-added,
 212                  * but since the reference points to to-space, that
 213                  * doesn't happen, and C+1 remains cleared: the remset
 214                  * is lost.
 215                  *
 216                  * There's at least two ways to fix this.  The easy
 217                  * one is to re-add the remset on the re-scan.  This
 218                  * is that - the following two lines of code.
 219                  *
 220                  * The proper solution appears to be to first make a
 221                  * copy of the cards before scanning a block, then to
 222                  * clear all the cards and scan from the copy, so no
 223                  * remsets will be overwritten.  Scanning objects at
 224                  * most once would be the icing on the cake.
 225                  */
 226                 if (!sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (obj))
 227                         sgen_add_to_global_remset (obj_slot, obj);
 228
 229                 return;
 230         }
 231 #endif
 232
 233         HEAVY_STAT (++stat_objects_copied_nursery);
 234
 235 #ifdef SGEN_SIMPLE_PAR_NURSERY
 236         copy = copy_object_no_checks_par (obj, queue);
 237 #else
 238         copy = copy_object_no_checks (obj, queue);
 239 #endif
 240 #ifdef SGEN_CONCURRENT_MAJOR
 241         /*
 242          * If an object is evacuated to the major heap and a reference to it, from the major
 243          * heap, updated, the concurrent major collector might follow that reference and
 244          * scan the new major object.  To make sure the object contents are seen by the
 245          * major collector we need this write barrier, so that the reference is seen after
 246          * the object.
 247          */
 248         STORE_STORE_FENCE;
 249 #endif
 250         SGEN_UPDATE_REFERENCE (obj_slot, copy);
 251 #ifndef SGEN_SIMPLE_NURSERY
 252         if (G_UNLIKELY (sgen_ptr_in_nursery (copy) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (copy)))
 253                 sgen_add_to_global_remset (obj_slot, copy);
 254 #else
 255         /* copy_object_no_checks () can return obj on OOM */
 256         if (G_UNLIKELY (obj == copy)) {
 257                 if (G_UNLIKELY (sgen_ptr_in_nursery (copy) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (copy)))
 258                         sgen_add_to_global_remset (obj_slot, copy);
 259         }
 260 #endif
 261 }