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
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
|
/*
* Copyright 2016 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkFixedAlloc_DEFINED
#define SkFixedAlloc_DEFINED
#include "SkTFitsIn.h"
#include "SkTypes.h"
#include <cstddef>
#include <new>
#include <type_traits>
#include <utility>
#include <vector>
// SkArenaAlloc allocates object and destroys the allocated objects when destroyed. It's designed
// to minimize the number of underlying block allocations. SkArenaAlloc allocates first out of an
// (optional) user-provided block of memory, and when that's exhausted it allocates on the heap,
// starting with an allocation of extraSize bytes. If your data (plus a small overhead) fits in
// the user-provided block, SkArenaAlloc never uses the heap, and if it fits in extraSize bytes,
// it'll use the heap only once. If you pass extraSize = 0, it allocates blocks for each call to
// make<T>.
//
// Examples:
//
// char block[mostCasesSize];
// SkArenaAlloc arena(block, almostAllCasesSize);
//
// If mostCasesSize is too large for the stack, you can use the following pattern.
//
// std::unique_ptr<char[]> block{new char[mostCasesSize]};
// SkArenaAlloc arena(block.get(), mostCasesSize, almostAllCasesSize);
//
// If the program only sometimes allocates memory, use the following.
//
// SkArenaAlloc arena(nullptr, 0, almostAllCasesSize);
//
// The storage does not necessarily need to be on the stack. Embedding the storage in a class also
// works.
//
// class Foo {
// char storage[mostCasesSize];
// SkArenaAlloc arena (storage, almostAllCasesSize);
// };
//
// In addition, the system is optimized to handle POD data including arrays of PODs (where
// POD is really data with no destructors). For POD data it has zero overhead per item, and a
// typical block overhead of 8 bytes. For non-POD objects there is a per item overhead of 4 bytes.
// For arrays of non-POD objects there is a per array overhead of typically 8 bytes. There is an
// addition overhead when switching from POD data to non-POD data of typically 8 bytes.
class SkArenaAlloc {
public:
SkArenaAlloc(char* block, size_t size, size_t extraSize = 0);
template <size_t kSize>
SkArenaAlloc(char (&block)[kSize], size_t extraSize = 0)
: SkArenaAlloc(block, kSize, extraSize)
{}
~SkArenaAlloc();
template <typename T, typename... Args>
T* make(Args&&... args) {
char* objStart;
if (skstd::is_trivially_destructible<T>::value) {
objStart = this->allocObject(sizeof(T), alignof(T));
fCursor = objStart + sizeof(T);
} else {
objStart = this->allocObjectWithFooter(sizeof(T) + sizeof(Footer), alignof(T));
size_t padding = objStart - fCursor;
// Advance to end of object to install footer.
fCursor = objStart + sizeof(T);
FooterAction* releaser = [](char* objEnd) {
char* objStart = objEnd - (sizeof(T) + sizeof(Footer));
((T*)objStart)->~T();
return objStart;
};
this->installFooter(releaser, padding);
}
// This must be last to make objects with nested use of this allocator work.
return new(objStart) T(std::forward<Args>(args)...);
}
template <typename T>
T* makeArrayDefault(size_t count) {
T* array = (T*)this->commonArrayAlloc<T>(count);
// If T is primitive then no initialization takes place.
for (size_t i = 0; i < count; i++) {
new (&array[i]) T;
}
return array;
}
template <typename T>
T* makeArray(size_t count) {
T* array = (T*)this->commonArrayAlloc<T>(count);
// If T is primitive then the memory is initialized. For example, an array of chars will
// be zeroed.
for (size_t i = 0; i < count; i++) {
new (&array[i]) T();
}
return array;
}
// Destroy all allocated objects, free any heap allocations.
void reset();
private:
using Footer = int32_t;
using FooterAction = char* (char*);
void installFooter(FooterAction* releaser, ptrdiff_t padding);
// N.B. Action is different than FooterAction. FooterAction expects the end of the Footer,
// and returns the start of the object. An Action expects the end of the *Object* and returns
// the start of the object.
template<typename Action>
void installIntFooter(ptrdiff_t size, ptrdiff_t padding) {
if (SkTFitsIn<int32_t>(size)) {
int32_t smallSize = static_cast<int32_t>(size);
memmove(fCursor, &smallSize, sizeof(int32_t));
fCursor += sizeof(int32_t);
this->installFooter(
[](char* footerEnd) {
char* objEnd = footerEnd - (sizeof(Footer) + sizeof(int32_t));
int32_t data;
memmove(&data, objEnd, sizeof(int32_t));
return Action()(objEnd, data);
},
padding);
} else {
memmove(fCursor, &size, sizeof(ptrdiff_t));
fCursor += sizeof(ptrdiff_t);
this->installFooter(
[](char* footerEnd) {
char* objEnd = footerEnd - (sizeof(Footer) + sizeof(ptrdiff_t));
ptrdiff_t data;
memmove(&data, objEnd, sizeof(ptrdiff_t));
return Action()(objEnd, data);
},
padding);
}
}
void ensureSpace(size_t size, size_t alignment);
char* allocObject(size_t size, size_t alignment);
char* allocObjectWithFooter(size_t sizeIncludingFooter, size_t alignment);
template <typename T>
char* commonArrayAlloc(size_t count) {
char* objStart;
size_t arraySize = count * sizeof(T);
SkASSERT(arraySize > 0);
if (skstd::is_trivially_destructible<T>::value) {
objStart = this->allocObject(arraySize, alignof(T));
fCursor = objStart + arraySize;
} else {
size_t countSize = SkTFitsIn<int32_t>(count) ? sizeof(int32_t) : sizeof(ptrdiff_t);
size_t totalSize = arraySize + sizeof(Footer) + countSize;
objStart = this->allocObjectWithFooter(totalSize, alignof(T));
size_t padding = objStart - fCursor;
// Advance to end of array to install footer.?
fCursor = objStart + arraySize;
this->installIntFooter<ArrayDestructor<T>> (count, padding);
}
return objStart;
}
char* callFooterAction(char* end);
static char* EndChain(char*);
template<typename T>
struct ArrayDestructor {
char* operator()(char* objEnd, ptrdiff_t count) {
char* objStart = objEnd - count * sizeof(T);
T* array = (T*) objStart;
for (int i = 0; i < count; i++) {
array[i].~T();
}
return objStart;
}
};
char* fDtorCursor;
char* fCursor;
char* fEnd;
size_t fExtraSize;
};
#endif//SkFixedAlloc_DEFINED
|
