2 * sgen-gray.h: Gray queue management.
4 * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
5 * Copyright (C) 2012 Xamarin Inc
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Library General Public
9 * License 2.0 as published by the Free Software Foundation;
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Library General Public License for more details.
16 * You should have received a copy of the GNU Library General Public
17 * License 2.0 along with this library; if not, write to the Free
18 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 #ifndef __MONO_SGEN_GRAY_H__
21 #define __MONO_SGEN_GRAY_H__
24 * This gray queue has to be as optimized as possible, because it is in the core of
25 * the mark/copy phase of the garbage collector. The memory access has then to be as
26 * cache friendly as possible. That's why we use a cursor based implementation.
28 * This simply consist in maintaining a pointer to the current element in the
29 * queue. In addition to using this cursor, we use a simple linked list of arrays,
30 * called sections, so that we have the cache friendliness of arrays without having
31 * the cost of memory reallocation of a dynaic array, not the cost of memory
32 * indirection of a linked list.
34 * This implementation also allows the dequeuing of a whole section at a time. This is
35 * for example used in the parallel GC because it would be too costly to take one element
36 * at a time. This imply the main constraint that, because we don't carry the cursor
37 * with the section, we still have to store the index of the last element. This is done
38 * through the 'size' field on the section, which default value is it's maximum value
39 * SGEN_GRAY_QUEUE_SECTION_SIZE. This field is updated in multiple cases :
40 * - section allocation : default value
41 * - object push : default value if we fill the current queue first
42 * - section dequeue : position of the cursor in the dequeued section
43 * - section enqueue : position of the cursor in the previously first section in the queue
45 * The previous implementation was an index based access where we would store the index
46 * of the last element in the section. This was less efficient because we would have
47 * to make 1 memory access for the index value, 1 for the base address of the objects
48 * array and another 1 for the actual value in the array.
51 /* SGEN_GRAY_QUEUE_HEADER_SIZE is number of machine words */
52 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
53 #define SGEN_GRAY_QUEUE_HEADER_SIZE 4
55 #define SGEN_GRAY_QUEUE_HEADER_SIZE 2
58 #define SGEN_GRAY_QUEUE_SECTION_SIZE (128 - SGEN_GRAY_QUEUE_HEADER_SIZE)
60 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
62 GRAY_QUEUE_SECTION_STATE_FLOATING,
63 GRAY_QUEUE_SECTION_STATE_ENQUEUED,
64 GRAY_QUEUE_SECTION_STATE_FREE_LIST,
65 GRAY_QUEUE_SECTION_STATE_FREED
66 } GrayQueueSectionState;
69 typedef struct _GrayQueueEntry GrayQueueEntry;
70 struct _GrayQueueEntry {
76 * This is a stack now instead of a queue, so the most recently added items are removed
77 * first, improving cache locality, and keeping the stack size manageable.
79 typedef struct _GrayQueueSection GrayQueueSection;
80 struct _GrayQueueSection {
81 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
83 * The dummy is here so that the state doesn't get overwritten
84 * by the internal allocator once the section is freed.
87 GrayQueueSectionState state;
90 GrayQueueSection *next;
91 GrayQueueEntry entries [SGEN_GRAY_QUEUE_SECTION_SIZE];
94 typedef struct _SgenGrayQueue SgenGrayQueue;
96 typedef void (*GrayQueueAllocPrepareFunc) (SgenGrayQueue*);
97 typedef void (*GrayQueueEnqueueCheckFunc) (char*);
99 struct _SgenGrayQueue {
100 GrayQueueEntry *cursor;
101 GrayQueueSection *first;
102 GrayQueueSection *free_list;
103 GrayQueueAllocPrepareFunc alloc_prepare_func;
104 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
105 GrayQueueEnqueueCheckFunc enqueue_check_func;
107 void *alloc_prepare_data;
110 typedef struct _SgenSectionGrayQueue SgenSectionGrayQueue;
112 struct _SgenSectionGrayQueue {
113 GrayQueueSection *first;
116 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
117 GrayQueueEnqueueCheckFunc enqueue_check_func;
121 #define GRAY_LAST_CURSOR_POSITION(s) ((s)->entries + SGEN_GRAY_QUEUE_SECTION_SIZE - 1)
122 #define GRAY_FIRST_CURSOR_POSITION(s) ((s)->entries)
124 #ifdef HEAVY_STATISTICS
125 extern unsigned long long stat_gray_queue_section_alloc;
126 extern unsigned long long stat_gray_queue_section_free;
127 extern unsigned long long stat_gray_queue_enqueue_fast_path;
128 extern unsigned long long stat_gray_queue_dequeue_fast_path;
129 extern unsigned long long stat_gray_queue_enqueue_slow_path;
130 extern unsigned long long stat_gray_queue_dequeue_slow_path;
133 void sgen_init_gray_queues (void) MONO_INTERNAL;
135 void sgen_gray_object_enqueue (SgenGrayQueue *queue, char *obj, mword desc) MONO_INTERNAL;
136 GrayQueueEntry sgen_gray_object_dequeue (SgenGrayQueue *queue) MONO_INTERNAL;
137 GrayQueueSection* sgen_gray_object_dequeue_section (SgenGrayQueue *queue) MONO_INTERNAL;
138 void sgen_gray_object_enqueue_section (SgenGrayQueue *queue, GrayQueueSection *section) MONO_INTERNAL;
139 void sgen_gray_object_queue_trim_free_list (SgenGrayQueue *queue) MONO_INTERNAL;
140 void sgen_gray_object_queue_init (SgenGrayQueue *queue, GrayQueueEnqueueCheckFunc enqueue_check_func) MONO_INTERNAL;
141 void sgen_gray_object_queue_init_invalid (SgenGrayQueue *queue) MONO_INTERNAL;
142 void sgen_gray_object_queue_init_with_alloc_prepare (SgenGrayQueue *queue, GrayQueueEnqueueCheckFunc enqueue_check_func,
143 GrayQueueAllocPrepareFunc func, void *data) MONO_INTERNAL;
144 void sgen_gray_object_queue_deinit (SgenGrayQueue *queue) MONO_INTERNAL;
145 void sgen_gray_object_queue_disable_alloc_prepare (SgenGrayQueue *queue) MONO_INTERNAL;
146 void sgen_gray_object_alloc_queue_section (SgenGrayQueue *queue) MONO_INTERNAL;
147 void sgen_gray_object_free_queue_section (GrayQueueSection *section) MONO_INTERNAL;
149 void sgen_section_gray_queue_init (SgenSectionGrayQueue *queue, gboolean locked,
150 GrayQueueEnqueueCheckFunc enqueue_check_func) MONO_INTERNAL;
151 gboolean sgen_section_gray_queue_is_empty (SgenSectionGrayQueue *queue) MONO_INTERNAL;
152 GrayQueueSection* sgen_section_gray_queue_dequeue (SgenSectionGrayQueue *queue) MONO_INTERNAL;
153 void sgen_section_gray_queue_enqueue (SgenSectionGrayQueue *queue, GrayQueueSection *section) MONO_INTERNAL;
155 static inline gboolean
156 sgen_gray_object_queue_is_empty (SgenGrayQueue *queue)
158 return queue->first == NULL;
161 static inline MONO_ALWAYS_INLINE void
162 GRAY_OBJECT_ENQUEUE (SgenGrayQueue *queue, char* obj, mword desc)
164 #if SGEN_MAX_DEBUG_LEVEL >= 9
165 sgen_gray_object_enqueue (queue, obj, desc);
167 if (G_UNLIKELY (!queue->first || queue->cursor == GRAY_LAST_CURSOR_POSITION (queue->first))) {
168 sgen_gray_object_enqueue (queue, obj, desc);
170 GrayQueueEntry entry = { obj, desc };
172 HEAVY_STAT (stat_gray_queue_enqueue_fast_path ++);
174 *++queue->cursor = entry;
175 #ifdef SGEN_HEAVY_BINARY_PROTOCOL
176 binary_protocol_gray_enqueue (queue, queue->cursor, obj);
182 static inline MONO_ALWAYS_INLINE void
183 GRAY_OBJECT_DEQUEUE (SgenGrayQueue *queue, char** obj, mword *desc)
185 GrayQueueEntry entry;
186 #if SGEN_MAX_DEBUG_LEVEL >= 9
187 entry = sgen_gray_object_enqueue (queue);
192 HEAVY_STAT (stat_gray_queue_dequeue_fast_path ++);
195 #ifdef SGEN_HEAVY_BINARY_PROTOCOL
196 binary_protocol_gray_dequeue (queue, queue->cursor, *obj);
198 } else if (G_UNLIKELY (queue->cursor == GRAY_FIRST_CURSOR_POSITION (queue->first))) {
199 entry = sgen_gray_object_dequeue (queue);
203 HEAVY_STAT (stat_gray_queue_dequeue_fast_path ++);
205 entry = *queue->cursor--;
208 #ifdef SGEN_HEAVY_BINARY_PROTOCOL
209 binary_protocol_gray_dequeue (queue, queue->cursor + 1, *obj);