3 * Gray queue management.
5 * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
6 * Copyright (C) 2012 Xamarin Inc
8 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
10 #ifndef __MONO_SGEN_GRAY_H__
11 #define __MONO_SGEN_GRAY_H__
13 #include "mono/sgen/sgen-protocol.h"
16 * This gray queue has to be as optimized as possible, because it is in the core of
17 * the mark/copy phase of the garbage collector. The memory access has then to be as
18 * cache friendly as possible. That's why we use a cursor based implementation.
20 * This simply consist in maintaining a pointer to the current element in the
21 * queue. In addition to using this cursor, we use a simple linked list of arrays,
22 * called sections, so that we have the cache friendliness of arrays without having
23 * the cost of memory reallocation of a dynaic array, not the cost of memory
24 * indirection of a linked list.
26 * This implementation also allows the dequeuing of a whole section at a time. This is
27 * for example used in the parallel GC because it would be too costly to take one element
28 * at a time. This imply the main constraint that, because we don't carry the cursor
29 * with the section, we still have to store the index of the last element. This is done
30 * through the 'size' field on the section, which default value is it's maximum value
31 * SGEN_GRAY_QUEUE_SECTION_SIZE. This field is updated in multiple cases :
32 * - section allocation : default value
33 * - object push : default value if we fill the current queue first
34 * - section dequeue : position of the cursor in the dequeued section
35 * - section enqueue : position of the cursor in the previously first section in the queue
37 * The previous implementation was an index based access where we would store the index
38 * of the last element in the section. This was less efficient because we would have
39 * to make 1 memory access for the index value, 1 for the base address of the objects
40 * array and another 1 for the actual value in the array.
43 /* SGEN_GRAY_QUEUE_HEADER_SIZE is number of machine words */
44 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
45 #define SGEN_GRAY_QUEUE_HEADER_SIZE 5
47 #define SGEN_GRAY_QUEUE_HEADER_SIZE 3
50 #define SGEN_GRAY_QUEUE_SECTION_SIZE (512 - SGEN_GRAY_QUEUE_HEADER_SIZE)
52 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
54 GRAY_QUEUE_SECTION_STATE_FLOATING
,
55 GRAY_QUEUE_SECTION_STATE_ENQUEUED
,
56 GRAY_QUEUE_SECTION_STATE_FREE_LIST
,
57 GRAY_QUEUE_SECTION_STATE_FREED
58 } GrayQueueSectionState
;
61 typedef struct _GrayQueueEntry GrayQueueEntry
;
62 struct _GrayQueueEntry
{
67 #define SGEN_GRAY_QUEUE_ENTRY(obj,desc) { (obj), (desc) }
69 #define GRAY_OBJECT_ENQUEUE_SERIAL(queue, obj, desc) (GRAY_OBJECT_ENQUEUE (queue, obj, desc, FALSE))
70 #define GRAY_OBJECT_ENQUEUE_PARALLEL(queue, obj, desc) (GRAY_OBJECT_ENQUEUE (queue, obj, desc, TRUE))
71 #define GRAY_OBJECT_DEQUEUE_SERIAL(queue, obj, desc) (GRAY_OBJECT_DEQUEUE (queue, obj, desc, FALSE))
72 #define GRAY_OBJECT_DEQUEUE_PARALLEL(queue, obj, desc) (GRAY_OBJECT_DEQUEUE (queue, obj, desc, TRUE))
75 * This is a stack now instead of a queue, so the most recently added items are removed
76 * first, improving cache locality, and keeping the stack size manageable.
78 typedef struct _GrayQueueSection GrayQueueSection
;
79 struct _GrayQueueSection
{
80 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
82 * The dummy is here so that the state doesn't get overwritten
83 * by the internal allocator once the section is freed.
86 GrayQueueSectionState state
;
89 GrayQueueSection
*next
, *prev
;
90 GrayQueueEntry entries
[SGEN_GRAY_QUEUE_SECTION_SIZE
];
93 typedef struct _SgenGrayQueue SgenGrayQueue
;
95 typedef void (*GrayQueueAllocPrepareFunc
) (SgenGrayQueue
*);
96 typedef void (*GrayQueueEnqueueCheckFunc
) (GCObject
*);
98 struct _SgenGrayQueue
{
99 GrayQueueEntry
*cursor
;
100 GrayQueueSection
*first
, *last
;
101 GrayQueueSection
*free_list
;
102 mono_mutex_t steal_mutex
;
104 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
105 GrayQueueEnqueueCheckFunc enqueue_check_func
;
109 typedef struct _SgenSectionGrayQueue SgenSectionGrayQueue
;
111 struct _SgenSectionGrayQueue
{
112 GrayQueueSection
*first
;
115 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
116 GrayQueueEnqueueCheckFunc enqueue_check_func
;
120 #define GRAY_LAST_CURSOR_POSITION(s) ((s)->entries + SGEN_GRAY_QUEUE_SECTION_SIZE - 1)
121 #define GRAY_FIRST_CURSOR_POSITION(s) ((s)->entries)
123 #ifdef HEAVY_STATISTICS
124 extern guint64 stat_gray_queue_section_alloc
;
125 extern guint64 stat_gray_queue_section_free
;
126 extern guint64 stat_gray_queue_enqueue_fast_path
;
127 extern guint64 stat_gray_queue_dequeue_fast_path
;
128 extern guint64 stat_gray_queue_enqueue_slow_path
;
129 extern guint64 stat_gray_queue_dequeue_slow_path
;
132 void sgen_init_gray_queues (void);
134 void sgen_gray_object_enqueue (SgenGrayQueue
*queue
, GCObject
*obj
, SgenDescriptor desc
, gboolean is_parallel
);
135 GrayQueueEntry
sgen_gray_object_dequeue (SgenGrayQueue
*queue
, gboolean is_parallel
);
136 GrayQueueSection
* sgen_gray_object_dequeue_section (SgenGrayQueue
*queue
);
137 GrayQueueSection
* sgen_gray_object_steal_section (SgenGrayQueue
*queue
);
138 void sgen_gray_object_spread (SgenGrayQueue
*queue
, int num_sections
);
139 void sgen_gray_object_enqueue_section (SgenGrayQueue
*queue
, GrayQueueSection
*section
, gboolean is_parallel
);
140 void sgen_gray_object_queue_trim_free_list (SgenGrayQueue
*queue
);
141 void sgen_gray_object_queue_init (SgenGrayQueue
*queue
, GrayQueueEnqueueCheckFunc enqueue_check_func
, gboolean reuse_free_list
);
142 void sgen_gray_object_queue_dispose (SgenGrayQueue
*queue
);
143 void sgen_gray_object_queue_deinit (SgenGrayQueue
*queue
);
144 void sgen_gray_object_alloc_queue_section (SgenGrayQueue
*queue
, gboolean is_parallel
);
145 void sgen_gray_object_free_queue_section (GrayQueueSection
*section
);
147 void sgen_section_gray_queue_init (SgenSectionGrayQueue
*queue
, gboolean locked
,
148 GrayQueueEnqueueCheckFunc enqueue_check_func
);
149 gboolean
sgen_section_gray_queue_is_empty (SgenSectionGrayQueue
*queue
);
150 GrayQueueSection
* sgen_section_gray_queue_dequeue (SgenSectionGrayQueue
*queue
);
151 void sgen_section_gray_queue_enqueue (SgenSectionGrayQueue
*queue
, GrayQueueSection
*section
);
153 gboolean
sgen_gray_object_fill_prefetch (SgenGrayQueue
*queue
);
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
, GCObject
*obj
, SgenDescriptor desc
, gboolean is_parallel
)
164 #if SGEN_MAX_DEBUG_LEVEL >= 9
165 sgen_gray_object_enqueue (queue
, obj
, desc
, is_parallel
);
167 if (G_UNLIKELY (!queue
->first
|| queue
->cursor
== GRAY_LAST_CURSOR_POSITION (queue
->first
))) {
168 sgen_gray_object_enqueue (queue
, obj
, desc
, is_parallel
);
170 GrayQueueEntry entry
= SGEN_GRAY_QUEUE_ENTRY (obj
, desc
);
172 HEAVY_STAT (stat_gray_queue_enqueue_fast_path
++);
174 *++queue
->cursor
= entry
;
175 #ifdef SGEN_HEAVY_BINARY_PROTOCOL
176 sgen_binary_protocol_gray_enqueue (queue
, queue
->cursor
, obj
);
182 static inline MONO_ALWAYS_INLINE
void
183 GRAY_OBJECT_DEQUEUE (SgenGrayQueue
*queue
, GCObject
** obj
, SgenDescriptor
*desc
, gboolean is_parallel
)
185 GrayQueueEntry entry
;
186 #if SGEN_MAX_DEBUG_LEVEL >= 9
187 entry
= sgen_gray_object_dequeue (queue
, is_parallel
);
192 HEAVY_STAT (stat_gray_queue_dequeue_fast_path
++);
195 } else if (G_UNLIKELY (queue
->cursor
== GRAY_FIRST_CURSOR_POSITION (queue
->first
))) {
196 entry
= sgen_gray_object_dequeue (queue
, is_parallel
);
200 HEAVY_STAT (stat_gray_queue_dequeue_fast_path
++);
202 entry
= *queue
->cursor
--;
205 #ifdef SGEN_HEAVY_BINARY_PROTOCOL
206 sgen_binary_protocol_gray_dequeue (queue
, queue
->cursor
+ 1, *obj
);