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
|
package cache
import (
"crypto/rand"
"math"
"math/big"
insecurerand "math/rand"
"os"
"runtime"
"time"
)
// This is an experimental and unexported (for now) attempt at making a cache
// with better algorithmic complexity than the standard one, namely by
// preventing write locks of the entire cache when an item is added. As of the
// time of writing, the overhead of selecting buckets results in cache
// operations being about twice as slow as for the standard cache with small
// total cache sizes, and faster for larger ones.
//
// See cache_test.go for a few benchmarks.
type unexportedShardedCache struct {
*shardedCache
}
type shardedCache struct {
seed uint32
m uint32
cs []*cache
janitor *shardedJanitor
}
// djb2 with better shuffling. 5x faster than FNV with the hash.Hash overhead.
func djb33(seed uint32, k string) uint32 {
var (
l = uint32(len(k))
d = 5381 + seed + l
i = uint32(0)
)
// Why is all this 5x faster than a for loop?
if l >= 4 {
for i < l-4 {
d = (d * 33) ^ uint32(k[i])
d = (d * 33) ^ uint32(k[i+1])
d = (d * 33) ^ uint32(k[i+2])
d = (d * 33) ^ uint32(k[i+3])
i += 4
}
}
switch l - i {
case 1:
case 2:
d = (d * 33) ^ uint32(k[i])
case 3:
d = (d * 33) ^ uint32(k[i])
d = (d * 33) ^ uint32(k[i+1])
case 4:
d = (d * 33) ^ uint32(k[i])
d = (d * 33) ^ uint32(k[i+1])
d = (d * 33) ^ uint32(k[i+2])
}
return d ^ (d >> 16)
}
func (sc *shardedCache) bucket(k string) *cache {
return sc.cs[djb33(sc.seed, k)%sc.m]
}
func (sc *shardedCache) Set(k string, x interface{}, d time.Duration) {
sc.bucket(k).Set(k, x, d)
}
func (sc *shardedCache) Add(k string, x interface{}, d time.Duration) error {
return sc.bucket(k).Add(k, x, d)
}
func (sc *shardedCache) Replace(k string, x interface{}, d time.Duration) error {
return sc.bucket(k).Replace(k, x, d)
}
func (sc *shardedCache) Get(k string) (interface{}, bool) {
return sc.bucket(k).Get(k)
}
func (sc *shardedCache) Increment(k string, n int64) error {
return sc.bucket(k).Increment(k, n)
}
func (sc *shardedCache) IncrementFloat(k string, n float64) error {
return sc.bucket(k).IncrementFloat(k, n)
}
func (sc *shardedCache) Decrement(k string, n int64) error {
return sc.bucket(k).Decrement(k, n)
}
func (sc *shardedCache) Delete(k string) {
sc.bucket(k).Delete(k)
}
func (sc *shardedCache) DeleteExpired() {
for _, v := range sc.cs {
v.DeleteExpired()
}
}
// Returns the items in the cache. This may include items that have expired,
// but have not yet been cleaned up. If this is significant, the Expiration
// fields of the items should be checked. Note that explicit synchronization
// is needed to use a cache and its corresponding Items() return values at
// the same time, as the maps are shared.
func (sc *shardedCache) Items() []map[string]Item {
res := make([]map[string]Item, len(sc.cs))
for i, v := range sc.cs {
res[i] = v.Items()
}
return res
}
func (sc *shardedCache) Flush() {
for _, v := range sc.cs {
v.Flush()
}
}
type shardedJanitor struct {
Interval time.Duration
stop chan bool
}
func (j *shardedJanitor) Run(sc *shardedCache) {
j.stop = make(chan bool)
tick := time.Tick(j.Interval)
for {
select {
case <-tick:
sc.DeleteExpired()
case <-j.stop:
return
}
}
}
func stopShardedJanitor(sc *unexportedShardedCache) {
sc.janitor.stop <- true
}
func runShardedJanitor(sc *shardedCache, ci time.Duration) {
j := &shardedJanitor{
Interval: ci,
}
sc.janitor = j
go j.Run(sc)
}
func newShardedCache(n int, de time.Duration) *shardedCache {
max := big.NewInt(0).SetUint64(uint64(math.MaxUint32))
rnd, err := rand.Int(rand.Reader, max)
var seed uint32
if err != nil {
os.Stderr.Write([]byte("WARNING: go-cache's newShardedCache failed to read from the system CSPRNG (/dev/urandom or equivalent.) Your system's security may be compromised. Continuing with an insecure seed.\n"))
seed = insecurerand.Uint32()
} else {
seed = uint32(rnd.Uint64())
}
sc := &shardedCache{
seed: seed,
m: uint32(n),
cs: make([]*cache, n),
}
for i := 0; i < n; i++ {
c := &cache{
defaultExpiration: de,
items: map[string]Item{},
}
sc.cs[i] = c
}
return sc
}
func unexportedNewSharded(defaultExpiration, cleanupInterval time.Duration, shards int) *unexportedShardedCache {
if defaultExpiration == 0 {
defaultExpiration = -1
}
sc := newShardedCache(shards, defaultExpiration)
SC := &unexportedShardedCache{sc}
if cleanupInterval > 0 {
runShardedJanitor(sc, cleanupInterval)
runtime.SetFinalizer(SC, stopShardedJanitor)
}
return SC
}
|
