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
|
// 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.
#ifndef V8_HEAP_SLOTS_BUFFER_H_
#define V8_HEAP_SLOTS_BUFFER_H_
#include "src/objects.h"
namespace v8 {
namespace internal {
// Forward declarations.
class SlotsBuffer;
// SlotsBufferAllocator manages the allocation and deallocation of slots buffer
// chunks and links them together. Slots buffer chunks are always created by the
// SlotsBufferAllocator.
class SlotsBufferAllocator {
public:
SlotsBuffer* AllocateBuffer(SlotsBuffer* next_buffer);
void DeallocateBuffer(SlotsBuffer* buffer);
void DeallocateChain(SlotsBuffer** buffer_address);
};
// SlotsBuffer records a sequence of slots that has to be updated
// after live objects were relocated from evacuation candidates.
// All slots are either untyped or typed:
// - Untyped slots are expected to contain a tagged object pointer.
// They are recorded by an address.
// - Typed slots are expected to contain an encoded pointer to a heap
// object where the way of encoding depends on the type of the slot.
// They are recorded as a pair (SlotType, slot address).
// We assume that zero-page is never mapped this allows us to distinguish
// untyped slots from typed slots during iteration by a simple comparison:
// if element of slots buffer is less than NUMBER_OF_SLOT_TYPES then it
// is the first element of typed slot's pair.
class SlotsBuffer {
public:
typedef Object** ObjectSlot;
explicit SlotsBuffer(SlotsBuffer* next_buffer)
: idx_(0), chain_length_(1), next_(next_buffer) {
if (next_ != NULL) {
chain_length_ = next_->chain_length_ + 1;
}
}
~SlotsBuffer() {}
void Add(ObjectSlot slot) {
DCHECK(0 <= idx_ && idx_ < kNumberOfElements);
#ifdef DEBUG
if (slot >= reinterpret_cast<ObjectSlot>(NUMBER_OF_SLOT_TYPES)) {
DCHECK_NOT_NULL(*slot);
}
#endif
slots_[idx_++] = slot;
}
ObjectSlot Get(intptr_t i) {
DCHECK(i >= 0 && i < kNumberOfElements);
return slots_[i];
}
size_t Size() {
DCHECK(idx_ <= kNumberOfElements);
return idx_;
}
enum SlotType {
EMBEDDED_OBJECT_SLOT,
OBJECT_SLOT,
RELOCATED_CODE_OBJECT,
CELL_TARGET_SLOT,
CODE_TARGET_SLOT,
CODE_ENTRY_SLOT,
DEBUG_TARGET_SLOT,
NUMBER_OF_SLOT_TYPES
};
static const char* SlotTypeToString(SlotType type) {
switch (type) {
case EMBEDDED_OBJECT_SLOT:
return "EMBEDDED_OBJECT_SLOT";
case OBJECT_SLOT:
return "OBJECT_SLOT";
case RELOCATED_CODE_OBJECT:
return "RELOCATED_CODE_OBJECT";
case CELL_TARGET_SLOT:
return "CELL_TARGET_SLOT";
case CODE_TARGET_SLOT:
return "CODE_TARGET_SLOT";
case CODE_ENTRY_SLOT:
return "CODE_ENTRY_SLOT";
case DEBUG_TARGET_SLOT:
return "DEBUG_TARGET_SLOT";
case NUMBER_OF_SLOT_TYPES:
return "NUMBER_OF_SLOT_TYPES";
}
return "UNKNOWN SlotType";
}
SlotsBuffer* next() { return next_; }
static int SizeOfChain(SlotsBuffer* buffer) {
if (buffer == NULL) return 0;
return static_cast<int>(buffer->idx_ +
(buffer->chain_length_ - 1) * kNumberOfElements);
}
inline bool IsFull() { return idx_ == kNumberOfElements; }
inline bool HasSpaceForTypedSlot() { return idx_ < kNumberOfElements - 1; }
enum AdditionMode { FAIL_ON_OVERFLOW, IGNORE_OVERFLOW };
static bool ChainLengthThresholdReached(SlotsBuffer* buffer) {
return buffer != NULL && buffer->chain_length_ >= kChainLengthThreshold;
}
INLINE(static bool AddTo(SlotsBufferAllocator* allocator,
SlotsBuffer** buffer_address, ObjectSlot slot,
AdditionMode mode)) {
SlotsBuffer* buffer = *buffer_address;
if (buffer == NULL || buffer->IsFull()) {
if (mode == FAIL_ON_OVERFLOW && ChainLengthThresholdReached(buffer)) {
allocator->DeallocateChain(buffer_address);
return false;
}
buffer = allocator->AllocateBuffer(buffer);
*buffer_address = buffer;
}
buffer->Add(slot);
return true;
}
static bool IsTypedSlot(ObjectSlot slot);
static bool AddTo(SlotsBufferAllocator* allocator,
SlotsBuffer** buffer_address, SlotType type, Address addr,
AdditionMode mode);
// Eliminates all stale entries from the slots buffer, i.e., slots that
// are not part of live objects anymore. This method must be called after
// marking, when the whole transitive closure is known and must be called
// before sweeping when mark bits are still intact.
static void RemoveInvalidSlots(Heap* heap, SlotsBuffer* buffer);
// Eliminate all slots that are within the given address range.
static void RemoveObjectSlots(Heap* heap, SlotsBuffer* buffer,
Address start_slot, Address end_slot);
// Ensures that there are no invalid slots in the chain of slots buffers.
static void VerifySlots(Heap* heap, SlotsBuffer* buffer);
static const int kNumberOfElements = 1021;
private:
static const int kChainLengthThreshold = 15;
intptr_t idx_;
intptr_t chain_length_;
SlotsBuffer* next_;
ObjectSlot slots_[kNumberOfElements];
};
} // namespace internal
} // namespace v8
#endif // V8_HEAP_SLOTS_BUFFER_H_
|
