blob: a608890fc3e1b0527dfdbe1823947caedca6bb10 (
plain)
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
|
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
#pragma once
#ifndef ROCKSDB_LITE
#include <atomic>
#include "util/mutexlock.h"
namespace ROCKSDB_NAMESPACE {
// LRU element definition
//
// Any object that needs to be part of the LRU algorithm should extend this
// class
template <class T>
struct LRUElement {
explicit LRUElement() : next_(nullptr), prev_(nullptr), refs_(0) {}
virtual ~LRUElement() { assert(!refs_); }
T* next_;
T* prev_;
std::atomic<size_t> refs_;
};
// LRU implementation
//
// In place LRU implementation. There is no copy or allocation involved when
// inserting or removing an element. This makes the data structure slim
template <class T>
class LRUList {
public:
virtual ~LRUList() {
MutexLock _(&lock_);
assert(!head_);
assert(!tail_);
}
// Push element into the LRU at the cold end
inline void Push(T* const t) {
assert(t);
assert(!t->next_);
assert(!t->prev_);
MutexLock _(&lock_);
assert((!head_ && !tail_) || (head_ && tail_));
assert(!head_ || !head_->prev_);
assert(!tail_ || !tail_->next_);
t->next_ = head_;
if (head_) {
head_->prev_ = t;
}
head_ = t;
if (!tail_) {
tail_ = t;
}
}
// Unlink the element from the LRU
inline void Unlink(T* const t) {
MutexLock _(&lock_);
UnlinkImpl(t);
}
// Evict an element from the LRU
inline T* Pop() {
MutexLock _(&lock_);
assert(tail_ && head_);
assert(!tail_->next_);
assert(!head_->prev_);
T* t = head_;
while (t && t->refs_) {
t = t->next_;
}
if (!t) {
// nothing can be evicted
return nullptr;
}
assert(!t->refs_);
// unlike the element
UnlinkImpl(t);
return t;
}
// Move the element from the front of the list to the back of the list
inline void Touch(T* const t) {
MutexLock _(&lock_);
UnlinkImpl(t);
PushBackImpl(t);
}
// Check if the LRU is empty
inline bool IsEmpty() const {
MutexLock _(&lock_);
return !head_ && !tail_;
}
private:
// Unlink an element from the LRU
void UnlinkImpl(T* const t) {
assert(t);
lock_.AssertHeld();
assert(head_ && tail_);
assert(t->prev_ || head_ == t);
assert(t->next_ || tail_ == t);
if (t->prev_) {
t->prev_->next_ = t->next_;
}
if (t->next_) {
t->next_->prev_ = t->prev_;
}
if (tail_ == t) {
tail_ = tail_->prev_;
}
if (head_ == t) {
head_ = head_->next_;
}
t->next_ = t->prev_ = nullptr;
}
// Insert an element at the hot end
inline void PushBack(T* const t) {
MutexLock _(&lock_);
PushBackImpl(t);
}
inline void PushBackImpl(T* const t) {
assert(t);
assert(!t->next_);
assert(!t->prev_);
lock_.AssertHeld();
assert((!head_ && !tail_) || (head_ && tail_));
assert(!head_ || !head_->prev_);
assert(!tail_ || !tail_->next_);
t->prev_ = tail_;
if (tail_) {
tail_->next_ = t;
}
tail_ = t;
if (!head_) {
head_ = tail_;
}
}
mutable port::Mutex lock_; // synchronization primitive
T* head_ = nullptr; // front (cold)
T* tail_ = nullptr; // back (hot)
};
} // namespace ROCKSDB_NAMESPACE
#endif
|
