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
|
/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
*/
#include "common/memorypool.h"
#include "common/util.h"
namespace Common {
enum {
INITIAL_CHUNKS_PER_PAGE = 8
};
static size_t adjustChunkSize(size_t chunkSize) {
// You must at least fit the pointer in the node (technically unneeded considering the next rounding statement)
chunkSize = MAX(chunkSize, sizeof(void *));
// There might be an alignment problem on some platforms when trying to load a void* on a non natural boundary
// so we round to the next sizeof(void *)
chunkSize = (chunkSize + sizeof(void *) - 1) & (~(sizeof(void *) - 1));
return chunkSize;
}
MemoryPool::MemoryPool(size_t chunkSize)
: _chunkSize(adjustChunkSize(chunkSize)) {
_next = nullptr;
_chunksPerPage = INITIAL_CHUNKS_PER_PAGE;
}
MemoryPool::~MemoryPool() {
#if 0
freeUnusedPages();
if (!_pages.empty())
warning("Memory leak found in pool");
#endif
for (size_t i = 0; i < _pages.size(); ++i)
::free(_pages[i].start);
}
void MemoryPool::allocPage() {
Page page;
// Allocate a new page
page.numChunks = _chunksPerPage;
assert(page.numChunks * _chunkSize < 16*1024*1024); // Refuse to allocate pages bigger than 16 MB
page.start = ::malloc(page.numChunks * _chunkSize);
assert(page.start);
_pages.push_back(page);
// Next time, we'll allocate a page twice as big as this one.
_chunksPerPage *= 2;
// Add the page to the pool of free chunk
addPageToPool(page);
}
void MemoryPool::addPageToPool(const Page &page) {
// Add all chunks of the new page to the linked list (pool) of free chunks
void *current = page.start;
for (size_t i = 1; i < page.numChunks; ++i) {
void *next = (byte *)current + _chunkSize;
*(void **)current = next;
current = next;
}
// Last chunk points to the old _next
*(void **)current = _next;
// From now on, the first free chunk is the first chunk of the new page
_next = page.start;
}
void *MemoryPool::allocChunk() {
// No free chunks left? Allocate a new page
if (!_next)
allocPage();
assert(_next);
void *result = _next;
_next = *(void **)result;
return result;
}
void MemoryPool::freeChunk(void *ptr) {
// Add the chunk back to (the start of) the list of free chunks
*(void **)ptr = _next;
_next = ptr;
}
// Technically not compliant C++ to compare unrelated pointers. In practice...
bool MemoryPool::isPointerInPage(void *ptr, const Page &page) {
return (ptr >= page.start) && (ptr < (char *)page.start + page.numChunks * _chunkSize);
}
void MemoryPool::freeUnusedPages() {
//std::sort(_pages.begin(), _pages.end());
Array<size_t> numberOfFreeChunksPerPage;
numberOfFreeChunksPerPage.resize(_pages.size());
for (size_t i = 0; i < numberOfFreeChunksPerPage.size(); ++i) {
numberOfFreeChunksPerPage[i] = 0;
}
// Compute for each page how many chunks in it are still in use.
void *iterator = _next;
while (iterator) {
// TODO: This should be a binary search (requiring us to keep _pages sorted)
for (size_t i = 0; i < _pages.size(); ++i) {
if (isPointerInPage(iterator, _pages[i])) {
++numberOfFreeChunksPerPage[i];
break;
}
}
iterator = *(void **)iterator;
}
// Free all pages which are not in use.
size_t freedPagesCount = 0;
for (size_t i = 0; i < _pages.size(); ++i) {
if (numberOfFreeChunksPerPage[i] == _pages[i].numChunks) {
// Remove all chunks of this page from the list of free chunks
void **iter2 = &_next;
while (*iter2) {
if (isPointerInPage(*iter2, _pages[i]))
*iter2 = **(void ***)iter2;
else
iter2 = *(void ***)iter2;
}
::free(_pages[i].start);
++freedPagesCount;
_pages[i].start = nullptr;
}
}
// debug("freed %d pages out of %d", (int)freedPagesCount, (int)_pages.size());
// Remove all now unused pages
size_t newSize = 0;
for (size_t i = 0; i < _pages.size(); ++i) {
if (_pages[i].start != nullptr) {
if (newSize != i)
_pages[newSize] = _pages[i];
++newSize;
}
}
_pages.resize(newSize);
// Reset _chunksPerPage
_chunksPerPage = INITIAL_CHUNKS_PER_PAGE;
for (size_t i = 0; i < _pages.size(); ++i) {
if (_chunksPerPage < _pages[i].numChunks)
_chunksPerPage = _pages[i].numChunks;
}
}
} // End of namespace Common
|
