2 * sgen-minor-copy-object.h: Copy functions for nursery collections.
4 * Copyright 2001-2003 Ximian, Inc
5 * Copyright 2003-2010 Novell, Inc.
6 * Copyright (C) 2012 Xamarin Inc
8 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
11 #define collector_pin_object(obj, queue) sgen_pin_object (obj, queue);
12 #define COLLECTOR_SERIAL_ALLOC_FOR_PROMOTION alloc_for_promotion
14 extern guint64 stat_nursery_copy_object_failed_to_space; /* from sgen-gc.c */
16 #include "sgen-copy-object.h"
19 * This is how the copying happens from the nursery to the old generation.
20 * We assume that at this time all the pinned objects have been identified and
22 * We run scan_object() for each pinned object so that each referenced
23 * objects if possible are copied. The new gray objects created can have
24 * scan_object() run on them right away, too.
25 * Then we run copy_object() for the precisely tracked roots. At this point
26 * all the roots are either gray or black. We run scan_object() on the gray
27 * objects until no more gray objects are created.
28 * At the end of the process we walk again the pinned list and we unmark
29 * the pinned flag. As we go we also create the list of free space for use
30 * in the next allocation runs.
32 * We need to remember objects from the old generation that point to the new one
33 * (or just addresses?).
35 * copy_object could be made into a macro once debugged (use inline for now).
38 static MONO_ALWAYS_INLINE void
39 SERIAL_COPY_OBJECT (GCObject **obj_slot, SgenGrayQueue *queue)
43 GCObject *obj = *obj_slot;
45 SGEN_ASSERT (9, current_collection_generation == GENERATION_NURSERY, "calling minor-serial-copy from a %d generation collection", current_collection_generation);
47 HEAVY_STAT (++stat_copy_object_called_nursery);
49 if (!sgen_ptr_in_nursery (obj)) {
50 HEAVY_STAT (++stat_nursery_copy_object_failed_from_space);
54 SGEN_LOG (9, "Precise copy of %p from %p", obj, obj_slot);
57 * Before we can copy the object we must make sure that we are
58 * allowed to, i.e. that the object not pinned, not already
59 * forwarded or belongs to the nursery To Space.
62 if ((forwarded = SGEN_OBJECT_IS_FORWARDED (obj))) {
63 SGEN_ASSERT (9, sgen_obj_get_descriptor (forwarded), "forwarded object %p has no gc descriptor", forwarded);
64 SGEN_LOG (9, " (already forwarded to %p)", forwarded);
65 HEAVY_STAT (++stat_nursery_copy_object_failed_forwarded);
66 SGEN_UPDATE_REFERENCE (obj_slot, forwarded);
69 if (G_UNLIKELY (SGEN_OBJECT_IS_PINNED (obj))) {
70 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "pinned object %p has no gc descriptor", obj);
71 SGEN_LOG (9, " (pinned, no change)");
72 HEAVY_STAT (++stat_nursery_copy_object_failed_pinned);
76 #ifndef SGEN_SIMPLE_NURSERY
77 if (sgen_nursery_is_to_space (obj)) {
78 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "to space object %p has no gc descriptor", obj);
79 SGEN_LOG (9, " (tospace, no change)");
80 HEAVY_STAT (++stat_nursery_copy_object_failed_to_space);
85 HEAVY_STAT (++stat_objects_copied_nursery);
87 copy = copy_object_no_checks (obj, queue);
88 SGEN_UPDATE_REFERENCE (obj_slot, copy);
92 * SERIAL_COPY_OBJECT_FROM_OBJ:
94 * Similar to SERIAL_COPY_OBJECT, but assumes that OBJ_SLOT is part of an object, so it handles global remsets as well.
96 static MONO_ALWAYS_INLINE void
97 SERIAL_COPY_OBJECT_FROM_OBJ (GCObject **obj_slot, SgenGrayQueue *queue)
100 GCObject *obj = *obj_slot;
103 SGEN_ASSERT (9, current_collection_generation == GENERATION_NURSERY, "calling minor-serial-copy-from-obj from a %d generation collection", current_collection_generation);
105 HEAVY_STAT (++stat_copy_object_called_nursery);
107 if (!sgen_ptr_in_nursery (obj)) {
108 HEAVY_STAT (++stat_nursery_copy_object_failed_from_space);
112 SGEN_LOG (9, "Precise copy of %p from %p", obj, obj_slot);
115 * Before we can copy the object we must make sure that we are
116 * allowed to, i.e. that the object not pinned, not already
117 * forwarded or belongs to the nursery To Space.
120 if ((forwarded = SGEN_OBJECT_IS_FORWARDED (obj))) {
121 SGEN_ASSERT (9, sgen_obj_get_descriptor (forwarded), "forwarded object %p has no gc descriptor", forwarded);
122 SGEN_LOG (9, " (already forwarded to %p)", forwarded);
123 HEAVY_STAT (++stat_nursery_copy_object_failed_forwarded);
124 /* See comment on STORE_STORE_FENCE below. */
126 SGEN_UPDATE_REFERENCE (obj_slot, forwarded);
127 #ifndef SGEN_SIMPLE_NURSERY
128 if (G_UNLIKELY (sgen_ptr_in_nursery (forwarded) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (forwarded)))
129 sgen_add_to_global_remset (obj_slot, forwarded);
133 if (G_UNLIKELY (SGEN_OBJECT_IS_PINNED (obj))) {
134 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "pinned object %p has no gc descriptor", obj);
135 SGEN_LOG (9, " (pinned, no change)");
136 HEAVY_STAT (++stat_nursery_copy_object_failed_pinned);
137 if (!sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (obj))
138 sgen_add_to_global_remset (obj_slot, obj);
142 #ifndef SGEN_SIMPLE_NURSERY
143 if (sgen_nursery_is_to_space (obj)) {
144 /* FIXME: all of these could just use `sgen_obj_get_descriptor_safe()` */
145 SGEN_ASSERT (9, sgen_vtable_get_descriptor (SGEN_LOAD_VTABLE(obj)), "to space object %p has no gc descriptor", obj);
146 SGEN_LOG (9, " (tospace, no change)");
147 HEAVY_STAT (++stat_nursery_copy_object_failed_to_space);
152 * The card table scanning code sometimes clears cards
153 * that have just been set for a global remset. In
154 * the split nursery the following situation can
157 * Let's say object A starts in card C but continues
158 * into C+1. Within A, at offset O there's a
159 * reference to a new nursery object X. A+O is in
160 * card C+1. Now card C is scanned, and as part of
161 * it, object A. The reference at A+O is processed by
162 * copying X into nursery to-space at Y. Since it's
163 * still in the nursery, a global remset must be added
164 * for A+O, so card C+1 is marked. Now, however, card
165 * C+1 is scanned, which means that it's cleared
166 * first. This wouldn't be terribly bad if reference
167 * A+O were re-scanned and the global remset re-added,
168 * but since the reference points to to-space, that
169 * doesn't happen, and C+1 remains cleared: the remset
172 * There's at least two ways to fix this. The easy
173 * one is to re-add the remset on the re-scan. This
174 * is that - the following two lines of code.
176 * The proper solution appears to be to first make a
177 * copy of the cards before scanning a block, then to
178 * clear all the cards and scan from the copy, so no
179 * remsets will be overwritten. Scanning objects at
180 * most once would be the icing on the cake.
182 if (!sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (obj))
183 sgen_add_to_global_remset (obj_slot, obj);
189 HEAVY_STAT (++stat_objects_copied_nursery);
191 copy = copy_object_no_checks (obj, queue);
193 * If an object is evacuated to the major heap and a reference to it, from the major
194 * heap, updated, the concurrent major collector might follow that reference and
195 * scan the new major object. To make sure the object contents are seen by the
196 * major collector we need this write barrier, so that the reference is seen after
199 * FIXME: This is only required if there's a concurrent major collection running,
200 * but we can't conditionally compile on that at the moment.
203 SGEN_UPDATE_REFERENCE (obj_slot, copy);
204 #ifndef SGEN_SIMPLE_NURSERY
205 if (G_UNLIKELY (sgen_ptr_in_nursery (copy) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (copy)))
206 sgen_add_to_global_remset (obj_slot, copy);
208 /* copy_object_no_checks () can return obj on OOM */
209 if (G_UNLIKELY (obj == copy)) {
210 if (G_UNLIKELY (sgen_ptr_in_nursery (copy) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (copy)))
211 sgen_add_to_global_remset (obj_slot, copy);
216 #define FILL_MINOR_COLLECTOR_COPY_OBJECT(collector) do { \
217 (collector)->serial_ops.copy_or_mark_object = SERIAL_COPY_OBJECT; \