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 #define SGEN_GRAY_QUEUE_SECTION_SIZE (128 - 3)
53 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
55 GRAY_QUEUE_SECTION_STATE_FLOATING,
56 GRAY_QUEUE_SECTION_STATE_ENQUEUED,
57 GRAY_QUEUE_SECTION_STATE_FREE_LIST,
58 GRAY_QUEUE_SECTION_STATE_FREED
59 } GrayQueueSectionState;
63 * This is a stack now instead of a queue, so the most recently added items are removed
64 * first, improving cache locality, and keeping the stack size manageable.
66 typedef struct _GrayQueueSection GrayQueueSection;
67 struct _GrayQueueSection {
68 #ifdef SGEN_CHECK_GRAY_OBJECT_SECTIONS
70 * The dummy is here so that the state doesn't get overwritten
71 * by the internal allocator once the section is freed.
74 GrayQueueSectionState state;
77 GrayQueueSection *next;
78 char *objects [SGEN_GRAY_QUEUE_SECTION_SIZE];
81 typedef struct _SgenGrayQueue SgenGrayQueue;
83 typedef void (*GrayQueueAllocPrepareFunc) (SgenGrayQueue*);
84 typedef void (*GrayQueueEnqueueCheckFunc) (char*);
86 struct _SgenGrayQueue {
88 GrayQueueSection *first;
89 GrayQueueSection *free_list;
90 GrayQueueAllocPrepareFunc alloc_prepare_func;
91 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
92 GrayQueueEnqueueCheckFunc enqueue_check_func;
94 void *alloc_prepare_data;
97 typedef struct _SgenSectionGrayQueue SgenSectionGrayQueue;
99 struct _SgenSectionGrayQueue {
100 GrayQueueSection *first;
103 #ifdef SGEN_CHECK_GRAY_OBJECT_ENQUEUE
104 GrayQueueEnqueueCheckFunc enqueue_check_func;
108 #define GRAY_LAST_CURSOR_POSITION(s) ((char**)(s)->objects + SGEN_GRAY_QUEUE_SECTION_SIZE - 1)
109 #define GRAY_FIRST_CURSOR_POSITION(s) ((char**)(s)->objects)
111 void sgen_gray_object_enqueue (SgenGrayQueue *queue, char *obj) MONO_INTERNAL;
112 char* sgen_gray_object_dequeue (SgenGrayQueue *queue) MONO_INTERNAL;
113 GrayQueueSection* sgen_gray_object_dequeue_section (SgenGrayQueue *queue) MONO_INTERNAL;
114 void sgen_gray_object_enqueue_section (SgenGrayQueue *queue, GrayQueueSection *section) MONO_INTERNAL;
115 void sgen_gray_object_queue_init (SgenGrayQueue *queue, GrayQueueEnqueueCheckFunc enqueue_check_func) MONO_INTERNAL;
116 void sgen_gray_object_queue_init_invalid (SgenGrayQueue *queue) MONO_INTERNAL;
117 void sgen_gray_object_queue_init_with_alloc_prepare (SgenGrayQueue *queue, GrayQueueEnqueueCheckFunc enqueue_check_func,
118 GrayQueueAllocPrepareFunc func, void *data) MONO_INTERNAL;
119 void sgen_gray_object_queue_deinit (SgenGrayQueue *queue) MONO_INTERNAL;
120 void sgen_gray_object_queue_disable_alloc_prepare (SgenGrayQueue *queue) MONO_INTERNAL;
121 void sgen_gray_object_alloc_queue_section (SgenGrayQueue *queue) MONO_INTERNAL;
122 void sgen_gray_object_free_queue_section (GrayQueueSection *section) MONO_INTERNAL;
124 void sgen_section_gray_queue_init (SgenSectionGrayQueue *queue, gboolean locked,
125 GrayQueueEnqueueCheckFunc enqueue_check_func) MONO_INTERNAL;
126 gboolean sgen_section_gray_queue_is_empty (SgenSectionGrayQueue *queue) MONO_INTERNAL;
127 GrayQueueSection* sgen_section_gray_queue_dequeue (SgenSectionGrayQueue *queue) MONO_INTERNAL;
128 void sgen_section_gray_queue_enqueue (SgenSectionGrayQueue *queue, GrayQueueSection *section) MONO_INTERNAL;
130 static inline gboolean
131 sgen_gray_object_queue_is_empty (SgenGrayQueue *queue)
133 return queue->first == NULL;