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
|
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/browser/loader/resource_buffer.h"
#include <math.h>
#include "base/logging.h"
namespace content {
// A circular buffer allocator.
//
// We keep track of the starting offset (alloc_start_) and the ending offset
// (alloc_end_). There are two layouts to keep in mind:
//
// #1:
// ------------[XXXXXXXXXXXXXXXXXXXXXXX]----
// ^ ^
// start end
//
// #2:
// XXXXXXXXXX]---------------------[XXXXXXXX
// ^ ^
// end start
//
// If end <= start, then we have the buffer wraparound case (depicted second).
// If the buffer is empty, then start and end will be set to -1.
//
// Allocations are always contiguous.
ResourceBuffer::ResourceBuffer()
: buf_size_(0),
min_alloc_size_(0),
max_alloc_size_(0),
alloc_start_(-1),
alloc_end_(-1) {
}
ResourceBuffer::~ResourceBuffer() {
}
bool ResourceBuffer::Initialize(int buffer_size,
int min_allocation_size,
int max_allocation_size) {
DCHECK(!IsInitialized());
// It would be wasteful if these are not multiples of min_allocation_size.
DCHECK_EQ(0, buffer_size % min_allocation_size);
DCHECK_EQ(0, max_allocation_size % min_allocation_size);
buf_size_ = buffer_size;
min_alloc_size_ = min_allocation_size;
max_alloc_size_ = max_allocation_size;
return shared_mem_.CreateAndMapAnonymous(buf_size_);
}
bool ResourceBuffer::IsInitialized() const {
return shared_mem_.memory() != NULL;
}
bool ResourceBuffer::ShareToProcess(
base::ProcessHandle process_handle,
base::SharedMemoryHandle* shared_memory_handle,
int* shared_memory_size) {
DCHECK(IsInitialized());
if (!shared_mem_.ShareToProcess(process_handle, shared_memory_handle))
return false;
*shared_memory_size = buf_size_;
return true;
}
bool ResourceBuffer::CanAllocate() const {
DCHECK(IsInitialized());
if (alloc_start_ == -1)
return true;
int diff = alloc_end_ - alloc_start_;
if (diff > 0)
return (buf_size_ - diff) >= min_alloc_size_;
return -diff >= min_alloc_size_;
}
char* ResourceBuffer::Allocate(int* size) {
DCHECK(CanAllocate());
int alloc_offset = 0;
int alloc_size;
if (alloc_start_ == -1) {
// This is the first allocation.
alloc_start_ = 0;
alloc_end_ = buf_size_;
alloc_size = buf_size_;
} else if (alloc_start_ < alloc_end_) {
// Append the next allocation if it fits. Otherwise, wraparound.
//
// NOTE: We could look to see if a larger allocation is possible by
// wrapping around sooner, but instead we just look to fill the space at
// the end of the buffer provided that meets the min_alloc_size_
// requirement.
//
if ((buf_size_ - alloc_end_) >= min_alloc_size_) {
alloc_offset = alloc_end_;
alloc_size = buf_size_ - alloc_end_;
alloc_end_ = buf_size_;
} else {
// It must be possible to allocate a least min_alloc_size_.
DCHECK(alloc_start_ >= min_alloc_size_);
alloc_size = alloc_start_;
alloc_end_ = alloc_start_;
}
} else {
// This is the wraparound case.
DCHECK(alloc_end_ < alloc_start_);
alloc_offset = alloc_end_;
alloc_size = alloc_start_ - alloc_end_;
alloc_end_ = alloc_start_;
}
// Make sure alloc_size does not exceed max_alloc_size_. We store the
// current value of alloc_size, so that we can use ShrinkLastAllocation to
// trim it back. This allows us to reuse the alloc_end_ adjustment logic.
alloc_sizes_.push(alloc_size);
if (alloc_size > max_alloc_size_) {
alloc_size = max_alloc_size_;
ShrinkLastAllocation(alloc_size);
}
*size = alloc_size;
return static_cast<char*>(shared_mem_.memory()) + alloc_offset;
}
int ResourceBuffer::GetLastAllocationOffset() const {
DCHECK(!alloc_sizes_.empty());
DCHECK(alloc_end_ >= alloc_sizes_.back());
return alloc_end_ - alloc_sizes_.back();
}
void ResourceBuffer::ShrinkLastAllocation(int new_size) {
DCHECK(!alloc_sizes_.empty());
int aligned_size = (new_size / min_alloc_size_) * min_alloc_size_;
if (aligned_size < new_size)
aligned_size += min_alloc_size_;
DCHECK_LE(new_size, aligned_size);
DCHECK_GE(alloc_sizes_.back(), aligned_size);
int* last_allocation_size = &alloc_sizes_.back();
alloc_end_ -= (*last_allocation_size - aligned_size);
*last_allocation_size = aligned_size;
}
void ResourceBuffer::RecycleLeastRecentlyAllocated() {
DCHECK(!alloc_sizes_.empty());
int allocation_size = alloc_sizes_.front();
alloc_sizes_.pop();
alloc_start_ += allocation_size;
DCHECK(alloc_start_ <= buf_size_);
if (alloc_start_ == alloc_end_) {
DCHECK(alloc_sizes_.empty());
alloc_start_ = -1;
alloc_end_ = -1;
} else if (alloc_start_ == buf_size_) {
DCHECK(!alloc_sizes_.empty());
alloc_start_ = 0;
}
}
} // namespace content
|
