1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
|
/* GObject - GLib Type, Object, Parameter and Signal Library
* Copyright (C) 2009 Benjamin Otte <otte@gnome.org>
*
* SPDX-License-Identifier: LGPL-2.1-or-later
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General
* Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/
#include "config.h"
#include "../glib/gvalgrind.h"
#include <string.h>
#include "gatomicarray.h"
/* A GAtomicArray is a growable, mutable array of data
* generally of the form of a header of a specific size and
* then an array of items of a fixed size.
*
* It is possible to do lock-less read transactions from the
* array without any protection against other reads or writes,
* but such read operation must be aware that the data in the
* atomic array can change at any time during the transaction,
* and only at the end can we verify if the transaction succeeded
* or not. Thus the reading transaction cannot for instance
* dereference a pointer in the array inside the transaction.
*
* The size of an array however cannot change during a read
* transaction.
*
* Writes to the array is done in a copy-update style, but there
* is no real protection against multiple writers overwriting each
* others updates, so writes must be protected by an external lock.
*/
G_LOCK_DEFINE_STATIC (array);
typedef struct _FreeListNode FreeListNode;
struct _FreeListNode {
FreeListNode *next;
};
/* This is really a list of array memory blocks, using the
* first item as the next pointer to chain them together.
* Protected by array lock */
static FreeListNode *freelist = NULL;
/* must hold array lock */
static gpointer
freelist_alloc (gsize size, gboolean reuse)
{
gpointer mem;
FreeListNode *free, **prev;
gsize real_size;
if (reuse)
{
for (free = freelist, prev = &freelist; free != NULL; prev = &free->next, free = free->next)
{
if (G_ATOMIC_ARRAY_DATA_SIZE (free) == size)
{
*prev = free->next;
return (gpointer)free;
}
}
}
real_size = sizeof (GAtomicArrayMetadata) + MAX (size, sizeof (FreeListNode));
mem = g_slice_alloc (real_size);
mem = ((char *) mem) + sizeof (GAtomicArrayMetadata);
G_ATOMIC_ARRAY_DATA_SIZE (mem) = size;
#if ENABLE_VALGRIND
VALGRIND_MALLOCLIKE_BLOCK (mem, real_size - sizeof (GAtomicArrayMetadata),
FALSE, FALSE);
#endif
return mem;
}
/* must hold array lock */
static void
freelist_free (gpointer mem)
{
FreeListNode *free;
free = mem;
free->next = freelist;
freelist = free;
}
void
_g_atomic_array_init (GAtomicArray *array)
{
array->data = NULL;
}
/* Get a copy of the data (if non-NULL) that
* can be changed and then re-applied with
* g_atomic_array_update().
*
* If additional_element_size is > 0 then
* then the new memory chunk is that much
* larger, or there were no data we return
* a chunk of header_size + additional_element_size.
* This means you can use this to grow the
* array part and it handles the first element
* being added automatically.
*
* We don't support shrinking arrays, as if
* we then re-grow we may reuse an old pointer
* value and confuse the transaction check.
*/
gpointer
_g_atomic_array_copy (GAtomicArray *array,
gsize header_size,
gsize additional_element_size)
{
guint8 *new, *old;
gsize old_size, new_size;
G_LOCK (array);
old = g_atomic_pointer_get (&array->data);
if (old)
{
old_size = G_ATOMIC_ARRAY_DATA_SIZE (old);
new_size = old_size + additional_element_size;
/* Don't reuse if copying to same size, as this may end
up reusing the same pointer for the same array thus
confusing the transaction check */
new = freelist_alloc (new_size, additional_element_size != 0);
memcpy (new, old, old_size);
}
else if (additional_element_size != 0)
{
new_size = header_size + additional_element_size;
new = freelist_alloc (new_size, TRUE);
}
else
new = NULL;
G_UNLOCK (array);
return new;
}
/* Replace the data in the array with the new data,
* freeing the old data (for reuse). The new data may
* not be smaller than the current data.
*/
void
_g_atomic_array_update (GAtomicArray *array,
gpointer new_data)
{
guint8 *old;
G_LOCK (array);
old = g_atomic_pointer_exchange (&array->data, new_data);
#ifdef G_DISABLE_ASSERT
if (old && G_ATOMIC_ARRAY_DATA_SIZE (new_data) < G_ATOMIC_ARRAY_DATA_SIZE (old))
{
g_atomic_pointer_set (&array->data, old);
g_return_if_reached ();
}
#else
g_assert (old == NULL || G_ATOMIC_ARRAY_DATA_SIZE (old) <= G_ATOMIC_ARRAY_DATA_SIZE (new_data));
#endif
if (old)
freelist_free (old);
G_UNLOCK (array);
}
|
