2 * sgen-pinning.c: The pin queue.
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.
16 #include "mono/sgen/sgen-gc.h"
17 #include "mono/sgen/sgen-pinning.h"
18 #include "mono/sgen/sgen-protocol.h"
19 #include "mono/sgen/sgen-pointer-queue.h"
20 #include "mono/sgen/sgen-client.h"
22 static SgenPointerQueue pin_queue;
23 static size_t last_num_pinned = 0;
25 * While we hold the pin_queue_mutex, all objects in pin_queue_objs will
26 * stay pinned, which means they can't move, therefore they can be scanned.
28 static SgenPointerQueue pin_queue_objs;
29 static mono_mutex_t pin_queue_mutex;
31 #define PIN_HASH_SIZE 1024
32 static void *pin_hash_filter [PIN_HASH_SIZE];
35 sgen_pinning_init (void)
37 mono_os_mutex_init (&pin_queue_mutex);
41 sgen_init_pinning (void)
43 mono_os_mutex_lock (&pin_queue_mutex);
44 memset (pin_hash_filter, 0, sizeof (pin_hash_filter));
45 pin_queue.mem_type = INTERNAL_MEM_PIN_QUEUE;
46 sgen_pointer_queue_clear (&pin_queue_objs);
50 sgen_finish_pinning (void)
52 last_num_pinned = pin_queue.next_slot;
53 sgen_pointer_queue_clear (&pin_queue);
54 mono_os_mutex_unlock (&pin_queue_mutex);
58 sgen_pinning_register_pinned_in_nursery (GCObject *obj)
60 sgen_pointer_queue_add (&pin_queue_objs, obj);
64 sgen_scan_pin_queue_objects (ScanCopyContext ctx)
67 ScanObjectFunc scan_func = ctx.ops->scan_object;
69 mono_os_mutex_lock (&pin_queue_mutex);
70 for (i = 0; i < pin_queue_objs.next_slot; ++i) {
71 GCObject *obj = (GCObject *)pin_queue_objs.data [i];
72 scan_func (obj, sgen_obj_get_descriptor_safe (obj), ctx.queue);
74 mono_os_mutex_unlock (&pin_queue_mutex);
78 sgen_pin_stage_ptr (void *ptr)
80 /*very simple multiplicative hash function, tons better than simple and'ng */
81 int hash_idx = ((mword)ptr * 1737350767) & (PIN_HASH_SIZE - 1);
82 if (pin_hash_filter [hash_idx] == ptr)
85 pin_hash_filter [hash_idx] = ptr;
87 sgen_pointer_queue_add (&pin_queue, ptr);
91 sgen_find_optimized_pin_queue_area (void *start, void *end, size_t *first_out, size_t *last_out)
93 size_t first = sgen_pointer_queue_search (&pin_queue, start);
94 size_t last = sgen_pointer_queue_search (&pin_queue, end);
95 SGEN_ASSERT (0, last == pin_queue.next_slot || pin_queue.data [last] >= end, "Pin queue search gone awry");
102 sgen_pinning_get_entry (size_t index)
104 SGEN_ASSERT (0, index <= pin_queue.next_slot, "Pin queue entry out of range");
105 return &pin_queue.data [index];
109 sgen_find_section_pin_queue_start_end (GCMemSection *section)
111 SGEN_LOG (6, "Pinning from section %p (%p-%p)", section, section->data, section->end_data);
113 sgen_find_optimized_pin_queue_area (section->data, section->end_data,
114 §ion->pin_queue_first_entry, §ion->pin_queue_last_entry);
116 SGEN_LOG (6, "Found %zd pinning addresses in section %p",
117 section->pin_queue_last_entry - section->pin_queue_first_entry, section);
120 /*This will setup the given section for the while pin queue. */
122 sgen_pinning_setup_section (GCMemSection *section)
124 section->pin_queue_first_entry = 0;
125 section->pin_queue_last_entry = pin_queue.next_slot;
129 sgen_pinning_trim_queue_to_section (GCMemSection *section)
131 SGEN_ASSERT (0, section->pin_queue_first_entry == 0, "Pin queue trimming assumes the whole pin queue is used by the nursery");
132 pin_queue.next_slot = section->pin_queue_last_entry;
136 * This is called when we've run out of memory during a major collection.
138 * After collecting potential pin entries and sorting the array, this is what it looks like:
140 * +--------------------+---------------------------------------------+--------------------+
141 * | major heap entries | nursery entries | major heap entries |
142 * +--------------------+---------------------------------------------+--------------------+
144 * Of course there might not be major heap entries before and/or after the nursery entries,
145 * depending on where the major heap sections are in the address space, and whether there
146 * were any potential pointers there.
148 * When we pin nursery objects, we compact the nursery part of the pin array, which leaves
149 * discarded entries after the ones that actually pointed to nursery objects:
151 * +--------------------+-----------------+---------------------------+--------------------+
152 * | major heap entries | nursery entries | discarded nursery entries | major heap entries |
153 * +--------------------+-----------------+---------------------------+--------------------+
155 * When, due to being out of memory, we late pin more objects, the pin array looks like
158 * +--------------------+-----------------+---------------------------+--------------------+--------------+
159 * | major heap entries | nursery entries | discarded nursery entries | major heap entries | late entries |
160 * +--------------------+-----------------+---------------------------+--------------------+--------------+
162 * This function gets rid of the discarded nursery entries by nulling them out. Note that
163 * we can late pin objects not only in the nursery but also in the major heap, which happens
164 * when evacuation fails.
167 sgen_pin_queue_clear_discarded_entries (GCMemSection *section, size_t max_pin_slot)
169 void **start = sgen_pinning_get_entry (section->pin_queue_last_entry);
170 void **end = sgen_pinning_get_entry (max_pin_slot);
173 for (; start < end; ++start) {
175 if ((char*)addr < section->data || (char*)addr > section->end_data)
181 /* reduce the info in the pin queue, removing duplicate pointers and sorting them */
183 sgen_optimize_pin_queue (void)
185 sgen_pointer_queue_sort_uniq (&pin_queue);
189 sgen_get_pinned_count (void)
191 return pin_queue.next_slot;
195 sgen_dump_pin_queue (void)
199 for (i = 0; i < last_num_pinned; ++i) {
200 GCObject *ptr = (GCObject *)pin_queue.data [i];
201 SGEN_LOG (3, "Bastard pinning obj %p (%s), size: %zd", ptr, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (ptr)), sgen_safe_object_get_size (ptr));
205 typedef struct _CementHashEntry CementHashEntry;
206 struct _CementHashEntry {
209 gboolean forced; /* if it should stay cemented after the finishing pause */
212 static CementHashEntry cement_hash [SGEN_CEMENT_HASH_SIZE];
214 static gboolean cement_enabled = TRUE;
217 sgen_cement_init (gboolean enabled)
219 cement_enabled = enabled;
223 sgen_cement_reset (void)
226 for (i = 0; i < SGEN_CEMENT_HASH_SIZE; i++) {
227 if (cement_hash [i].forced) {
228 cement_hash [i].forced = FALSE;
230 cement_hash [i].obj = NULL;
231 cement_hash [i].count = 0;
234 binary_protocol_cement_reset ();
239 * The pin_queue should be full and sorted, without entries from the cemented
240 * objects. We traverse the cement hash and check if each object is pinned in
241 * the pin_queue (the pin_queue contains entries between obj and obj+obj_len)
244 sgen_cement_force_pinned (void)
251 for (i = 0; i < SGEN_CEMENT_HASH_SIZE; i++) {
252 GCObject *obj = cement_hash [i].obj;
256 if (cement_hash [i].count < SGEN_CEMENT_THRESHOLD)
258 SGEN_ASSERT (0, !cement_hash [i].forced, "Why do we have a forced cemented object before forcing ?");
260 /* Returns the index of the target or of the first element greater than it */
261 index = sgen_pointer_queue_search (&pin_queue, obj);
262 if (index == pin_queue.next_slot)
264 SGEN_ASSERT (0, pin_queue.data [index] >= (gpointer)obj, "Binary search should return a pointer greater than the search target");
265 if (pin_queue.data [index] < (gpointer)((char*)obj + sgen_safe_object_get_size (obj)))
266 cement_hash [i].forced = TRUE;
271 sgen_cement_is_forced (GCObject *obj)
273 guint hv = sgen_aligned_addr_hash (obj);
274 int i = SGEN_CEMENT_HASH (hv);
276 SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Looking up cementing for non-nursery objects makes no sense");
281 if (!cement_hash [i].obj)
283 if (cement_hash [i].obj != obj)
286 return cement_hash [i].forced;
290 sgen_cement_lookup (GCObject *obj)
292 guint hv = sgen_aligned_addr_hash (obj);
293 int i = SGEN_CEMENT_HASH (hv);
295 SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Looking up cementing for non-nursery objects makes no sense");
300 if (!cement_hash [i].obj)
302 if (cement_hash [i].obj != obj)
305 return cement_hash [i].count >= SGEN_CEMENT_THRESHOLD;
309 sgen_cement_lookup_or_register (GCObject *obj)
313 CementHashEntry *hash = cement_hash;
318 hv = sgen_aligned_addr_hash (obj);
319 i = SGEN_CEMENT_HASH (hv);
321 SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Can only cement pointers to nursery objects");
324 SGEN_ASSERT (5, !hash [i].count, "Cementing hash inconsistent");
326 } else if (hash [i].obj != obj) {
330 if (hash [i].count >= SGEN_CEMENT_THRESHOLD)
334 if (hash [i].count == SGEN_CEMENT_THRESHOLD) {
335 SGEN_ASSERT (9, sgen_get_current_collection_generation () >= 0, "We can only cement objects when we're in a collection pause.");
336 SGEN_ASSERT (9, SGEN_OBJECT_IS_PINNED (obj), "Can only cement pinned objects");
337 SGEN_CEMENT_OBJECT (obj);
339 binary_protocol_cement (obj, (gpointer)SGEN_LOAD_VTABLE (obj),
340 (int)sgen_safe_object_get_size (obj));
347 pin_from_hash (CementHashEntry *hash, gboolean has_been_reset)
350 for (i = 0; i < SGEN_CEMENT_HASH_SIZE; ++i) {
355 SGEN_ASSERT (5, hash [i].count >= SGEN_CEMENT_THRESHOLD, "Cementing hash inconsistent");
357 sgen_pin_stage_ptr (hash [i].obj);
358 binary_protocol_cement_stage (hash [i].obj);
359 /* FIXME: do pin stats if enabled */
361 SGEN_CEMENT_OBJECT (hash [i].obj);
366 sgen_pin_cemented_objects (void)
368 pin_from_hash (cement_hash, TRUE);
372 sgen_cement_clear_below_threshold (void)
375 for (i = 0; i < SGEN_CEMENT_HASH_SIZE; ++i) {
376 if (cement_hash [i].count < SGEN_CEMENT_THRESHOLD) {
377 cement_hash [i].obj = NULL;
378 cement_hash [i].count = 0;
383 #endif /* HAVE_SGEN_GC */