mono/sgen/sgen-gray.h

   1 /*
   2  * sgen-gray.h: Gray queue management.
   3  *
   4  * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
   5  * Copyright (C) 2012 Xamarin Inc
   6  *
   7  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
   8  */
   9 #ifndef __MONO_SGEN_GRAY_H__
  10 #define __MONO_SGEN_GRAY_H__
  11
  12 #include "mono/sgen/sgen-protocol.h"
  13
  14 /*
  15  * This gray queue has to be as optimized as possible, because it is in the core of
  16  * the mark/copy phase of the garbage collector. The memory access has then to be as
  17  * cache friendly as possible. That's why we use a cursor based implementation.
  18  *
  19  * This simply consist in maintaining a pointer to the current element in the
  20  * queue. In addition to using this cursor, we use a simple linked list of arrays,
  21  * called sections, so that we have the cache friendliness of arrays without having
  22  * the cost of memory reallocation of a dynaic array, not the cost of memory
  23  * indirection of a linked list.
  24  *
  25  * This implementation also allows the dequeuing of a whole section at a time. This is
  26  * for example used in the parallel GC because it would be too costly to take one element
  27  * at a time. This imply the main constraint that, because we don't carry the cursor
  28  * with the section, we still have to store the index of the last element. This is done
  29  * through the 'size' field on the section, which default value is it's maximum value
  30  * SGEN_GRAY_QUEUE_SECTION_SIZE. This field is updated in multiple cases :
  31  *  - section allocation : default value
  32  *  - object push : default value if we fill the current queue first
  33  *  - section dequeue : position of the cursor in the dequeued section
  34  *  - section enqueue : position of the cursor in the previously first section in the queue
  35  *
  36  * The previous implementation was an index based access where we would store the index
  37  * of the last element in the section. This was less efficient because we would have
  38  * to make 1 memory access for the index value, 1 for the base address of the objects
  39  * array and another 1 for the actual value in the array.
  40  */
  41
  42 /* SGEN_GRAY_QUEUE_HEADER_SIZE is number of machine words */
  43 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
  44 #define SGEN_GRAY_QUEUE_HEADER_SIZE     5
  45 #else
  46 #define SGEN_GRAY_QUEUE_HEADER_SIZE     3
  47 #endif
  48
  49 #define SGEN_GRAY_QUEUE_SECTION_SIZE    (128 - SGEN_GRAY_QUEUE_HEADER_SIZE)
  50
  51 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
  52 typedef enum {
  53         GRAY_QUEUE_SECTION_STATE_FLOATING,
  54         GRAY_QUEUE_SECTION_STATE_ENQUEUED,
  55         GRAY_QUEUE_SECTION_STATE_FREE_LIST,
  56         GRAY_QUEUE_SECTION_STATE_FREED
  57 } GrayQueueSectionState;
  58 #endif
  59
  60 typedef struct _GrayQueueEntry GrayQueueEntry;
  61 struct _GrayQueueEntry {
  62         GCObject *obj;
  63         SgenDescriptor desc;
  64 };
  65
  66 #define SGEN_GRAY_QUEUE_ENTRY(obj,desc) { (obj), (desc) }
  67
  68 #define GRAY_OBJECT_ENQUEUE_SERIAL(queue, obj, desc) (GRAY_OBJECT_ENQUEUE (queue, obj, desc, FALSE))
  69 #define GRAY_OBJECT_ENQUEUE_PARALLEL(queue, obj, desc) (GRAY_OBJECT_ENQUEUE (queue, obj, desc, TRUE))
  70 #define GRAY_OBJECT_DEQUEUE_SERIAL(queue, obj, desc) (GRAY_OBJECT_DEQUEUE (queue, obj, desc, FALSE))
  71 #define GRAY_OBJECT_DEQUEUE_PARALLEL(queue, obj, desc) (GRAY_OBJECT_DEQUEUE (queue, obj, desc, TRUE))
  72
  73 /*
  74  * This is a stack now instead of a queue, so the most recently added items are removed
  75  * first, improving cache locality, and keeping the stack size manageable.
  76  */
  77 typedef struct _GrayQueueSection GrayQueueSection;
  78 struct _GrayQueueSection {
  79 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
  80         /*
  81          * The dummy is here so that the state doesn't get overwritten
  82          * by the internal allocator once the section is freed.
  83          */
  84         int dummy;
  85         GrayQueueSectionState state;
  86 #endif
  87         int size;
  88         GrayQueueSection *next, *prev;
  89         GrayQueueEntry entries [SGEN_GRAY_QUEUE_SECTION_SIZE];
  90 };
  91
  92 typedef struct _SgenGrayQueue SgenGrayQueue;
  93
  94 typedef void (*GrayQueueAllocPrepareFunc) (SgenGrayQueue*);
  95 typedef void (*GrayQueueEnqueueCheckFunc) (GCObject*);
  96
  97 struct _SgenGrayQueue {
  98         GrayQueueEntry *cursor;
  99         GrayQueueSection *first, *last;
 100         GrayQueueSection *free_list;
 101         mono_mutex_t steal_mutex;
 102         gint32 num_sections;
 103 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
 104         GrayQueueEnqueueCheckFunc enqueue_check_func;
 105 #endif
 106 };
 107
 108 typedef struct _SgenSectionGrayQueue SgenSectionGrayQueue;
 109
 110 struct _SgenSectionGrayQueue {
 111         GrayQueueSection *first;
 112         gboolean locked;
 113         mono_mutex_t lock;
 114 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
 115         GrayQueueEnqueueCheckFunc enqueue_check_func;
 116 #endif
 117 };
 118
 119 #define GRAY_LAST_CURSOR_POSITION(s) ((s)->entries + SGEN_GRAY_QUEUE_SECTION_SIZE - 1)
 120 #define GRAY_FIRST_CURSOR_POSITION(s) ((s)->entries)
 121
 122 #ifdef HEAVY_STATISTICS
 123 extern guint64 stat_gray_queue_section_alloc;
 124 extern guint64 stat_gray_queue_section_free;
 125 extern guint64 stat_gray_queue_enqueue_fast_path;
 126 extern guint64 stat_gray_queue_dequeue_fast_path;
 127 extern guint64 stat_gray_queue_enqueue_slow_path;
 128 extern guint64 stat_gray_queue_dequeue_slow_path;
 129 #endif
 130
 131 void sgen_init_gray_queues (void);
 132
 133 void sgen_gray_object_enqueue (SgenGrayQueue *queue, GCObject *obj, SgenDescriptor desc, gboolean is_parallel);
 134 GrayQueueEntry sgen_gray_object_dequeue (SgenGrayQueue *queue, gboolean is_parallel);
 135 GrayQueueSection* sgen_gray_object_dequeue_section (SgenGrayQueue *queue);
 136 GrayQueueSection* sgen_gray_object_steal_section (SgenGrayQueue *queue);
 137 void sgen_gray_object_spread (SgenGrayQueue *queue, int num_sections);
 138 void sgen_gray_object_enqueue_section (SgenGrayQueue *queue, GrayQueueSection *section, gboolean is_parallel);
 139 void sgen_gray_object_queue_trim_free_list (SgenGrayQueue *queue);
 140 void sgen_gray_object_queue_init (SgenGrayQueue *queue, GrayQueueEnqueueCheckFunc enqueue_check_func, gboolean reuse_free_list);
 141 void sgen_gray_object_queue_dispose (SgenGrayQueue *queue);
 142 void sgen_gray_object_queue_deinit (SgenGrayQueue *queue);
 143 void sgen_gray_object_alloc_queue_section (SgenGrayQueue *queue, gboolean is_parallel);
 144 void sgen_gray_object_free_queue_section (GrayQueueSection *section);
 145
 146 void sgen_section_gray_queue_init (SgenSectionGrayQueue *queue, gboolean locked,
 147                 GrayQueueEnqueueCheckFunc enqueue_check_func);
 148 gboolean sgen_section_gray_queue_is_empty (SgenSectionGrayQueue *queue);
 149 GrayQueueSection* sgen_section_gray_queue_dequeue (SgenSectionGrayQueue *queue);
 150 void sgen_section_gray_queue_enqueue (SgenSectionGrayQueue *queue, GrayQueueSection *section);
 151
 152 gboolean sgen_gray_object_fill_prefetch (SgenGrayQueue *queue);
 153
 154 static inline gboolean
 155 sgen_gray_object_queue_is_empty (SgenGrayQueue *queue)
 156 {
 157         return queue->first == NULL;
 158 }
 159
 160 static inline MONO_ALWAYS_INLINE void
 161 GRAY_OBJECT_ENQUEUE (SgenGrayQueue *queue, GCObject *obj, SgenDescriptor desc, gboolean is_parallel)
 162 {
 163 #if SGEN_MAX_DEBUG_LEVEL >= 9
 164         sgen_gray_object_enqueue (queue, obj, desc, is_parallel);
 165 #else
 166         if (G_UNLIKELY (!queue->first || queue->cursor == GRAY_LAST_CURSOR_POSITION (queue->first))) {
 167                 sgen_gray_object_enqueue (queue, obj, desc, is_parallel);
 168         } else {
 169                 GrayQueueEntry entry = SGEN_GRAY_QUEUE_ENTRY (obj, desc);
 170
 171                 HEAVY_STAT (stat_gray_queue_enqueue_fast_path ++);
 172
 173                 *++queue->cursor = entry;
 174 #ifdef SGEN_HEAVY_BINARY_PROTOCOL
 175                 binary_protocol_gray_enqueue (queue, queue->cursor, obj);
 176 #endif
 177         }
 178 #endif
 179 }
 180
 181 static inline MONO_ALWAYS_INLINE void
 182 GRAY_OBJECT_DEQUEUE (SgenGrayQueue *queue, GCObject** obj, SgenDescriptor *desc, gboolean is_parallel)
 183 {
 184         GrayQueueEntry entry;
 185 #if SGEN_MAX_DEBUG_LEVEL >= 9
 186         entry = sgen_gray_object_dequeue (queue, is_parallel);
 187         *obj = entry.obj;
 188         *desc = entry.desc;
 189 #else
 190         if (!queue->first) {
 191                 HEAVY_STAT (stat_gray_queue_dequeue_fast_path ++);
 192
 193                 *obj = NULL;
 194         } else if (G_UNLIKELY (queue->cursor == GRAY_FIRST_CURSOR_POSITION (queue->first))) {
 195                 entry = sgen_gray_object_dequeue (queue, is_parallel);
 196                 *obj = entry.obj;
 197                 *desc = entry.desc;
 198         } else {
 199                 HEAVY_STAT (stat_gray_queue_dequeue_fast_path ++);
 200
 201                 entry = *queue->cursor--;
 202                 *obj = entry.obj;
 203                 *desc = entry.desc;
 204 #ifdef SGEN_HEAVY_BINARY_PROTOCOL
 205                 binary_protocol_gray_dequeue (queue, queue->cursor + 1, *obj);
 206 #endif
 207         }
 208 #endif
 209 }
 210
 211 #endif