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
|
// Copyright 2015 the V8 project 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 "src/v8.h"
#include "src/heap/heap.h"
#include "src/heap/identity-map.h"
namespace v8 {
namespace internal {
static const int kInitialIdentityMapSize = 4;
static const int kResizeFactor = 4;
IdentityMapBase::~IdentityMapBase() {
if (keys_) {
Heap::OptionalRelocationLock lock(heap_, concurrent_);
heap_->UnregisterStrongRoots(keys_);
}
}
IdentityMapBase::RawEntry IdentityMapBase::Lookup(Handle<Object> key) {
AllowHandleDereference for_lookup;
int index = LookupIndex(*key);
return index >= 0 ? &values_[index] : nullptr;
}
IdentityMapBase::RawEntry IdentityMapBase::Insert(Handle<Object> key) {
AllowHandleDereference for_lookup;
int index = InsertIndex(*key);
DCHECK_GE(index, 0);
return &values_[index];
}
int IdentityMapBase::Hash(Object* address) {
uintptr_t raw_address = reinterpret_cast<uintptr_t>(address);
CHECK_NE(0U, raw_address); // Cannot store Smi 0 as a key here, sorry.
// Xor some of the upper bits, since the lower 2 or 3 are usually aligned.
return static_cast<int>((raw_address >> 11) ^ raw_address);
}
int IdentityMapBase::LookupIndex(Object* address) {
int start = Hash(address) & mask_;
for (int index = start; index < size_; index++) {
if (keys_[index] == address) return index; // Found.
if (keys_[index] == nullptr) return -1; // Not found.
}
for (int index = 0; index < start; index++) {
if (keys_[index] == address) return index; // Found.
if (keys_[index] == nullptr) return -1; // Not found.
}
return -1;
}
int IdentityMapBase::InsertIndex(Object* address) {
while (true) {
int start = Hash(address) & mask_;
int limit = size_ / 2;
// Search up to {limit} entries.
for (int index = start; --limit > 0; index = (index + 1) & mask_) {
if (keys_[index] == address) return index; // Found.
if (keys_[index] == nullptr) { // Free entry.
keys_[index] = address;
return index;
}
}
Resize(); // Should only have to resize once, since we grow 4x.
}
UNREACHABLE();
return -1;
}
// Searches this map for the given key using the object's address
// as the identity, returning:
// found => a pointer to the storage location for the value
// not found => a pointer to a new storage location for the value
IdentityMapBase::RawEntry IdentityMapBase::GetEntry(Handle<Object> key) {
Heap::OptionalRelocationLock lock(heap_, concurrent_);
RawEntry result;
if (size_ == 0) {
// Allocate the initial storage for keys and values.
size_ = kInitialIdentityMapSize;
mask_ = kInitialIdentityMapSize - 1;
gc_counter_ = heap_->gc_count();
keys_ = zone_->NewArray<Object*>(size_);
memset(keys_, 0, sizeof(Object*) * size_);
values_ = zone_->NewArray<void*>(size_);
memset(values_, 0, sizeof(void*) * size_);
heap_->RegisterStrongRoots(keys_, keys_ + size_);
result = Insert(key);
} else {
// Perform an optimistic lookup.
result = Lookup(key);
if (result == nullptr) {
// Miss; rehash if there was a GC, then insert.
if (gc_counter_ != heap_->gc_count()) Rehash();
result = Insert(key);
}
}
return result;
}
// Searches this map for the given key using the object's address
// as the identity, returning:
// found => a pointer to the storage location for the value
// not found => {nullptr}
IdentityMapBase::RawEntry IdentityMapBase::FindEntry(Handle<Object> key) {
if (size_ == 0) return nullptr;
Heap::OptionalRelocationLock lock(heap_, concurrent_);
RawEntry result = Lookup(key);
if (result == nullptr && gc_counter_ != heap_->gc_count()) {
Rehash(); // Rehash is expensive, so only do it in case of a miss.
result = Lookup(key);
}
return result;
}
void IdentityMapBase::Rehash() {
// Record the current GC counter.
gc_counter_ = heap_->gc_count();
// Assume that most objects won't be moved.
ZoneVector<std::pair<Object*, void*>> reinsert(zone_);
// Search the table looking for keys that wouldn't be found with their
// current hashcode and evacuate them.
int last_empty = -1;
for (int i = 0; i < size_; i++) {
if (keys_[i] == nullptr) {
last_empty = i;
} else {
int pos = Hash(keys_[i]) & mask_;
if (pos <= last_empty || pos > i) {
// Evacuate an entry that is in the wrong place.
reinsert.push_back(std::pair<Object*, void*>(keys_[i], values_[i]));
keys_[i] = nullptr;
values_[i] = nullptr;
last_empty = i;
}
}
}
// Reinsert all the key/value pairs that were in the wrong place.
for (auto pair : reinsert) {
int index = InsertIndex(pair.first);
DCHECK_GE(index, 0);
DCHECK_NULL(values_[index]);
values_[index] = pair.second;
}
}
void IdentityMapBase::Resize() {
// Grow the internal storage and reinsert all the key/value pairs.
int old_size = size_;
Object** old_keys = keys_;
void** old_values = values_;
size_ = size_ * kResizeFactor;
mask_ = size_ - 1;
gc_counter_ = heap_->gc_count();
CHECK_LE(size_, (1024 * 1024 * 16)); // that would be extreme...
keys_ = zone_->NewArray<Object*>(size_);
memset(keys_, 0, sizeof(Object*) * size_);
values_ = zone_->NewArray<void*>(size_);
memset(values_, 0, sizeof(void*) * size_);
for (int i = 0; i < old_size; i++) {
if (old_keys[i] == nullptr) continue;
int index = InsertIndex(old_keys[i]);
DCHECK_GE(index, 0);
values_[index] = old_values[i];
}
// Unregister old keys and register new keys.
heap_->UnregisterStrongRoots(old_keys);
heap_->RegisterStrongRoots(keys_, keys_ + size_);
}
} // namespace internal
} // namespace v8
|
