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
|
package xpath
import (
"regexp"
"sync"
)
type loadFunc func(key interface{}) (interface{}, error)
const (
defaultCap = 65536
)
// The reason we're building a simple capacity-resetting loading cache (when capacity reached) instead of using
// something like github.com/hashicorp/golang-lru is primarily due to (not wanting to create) external dependency.
// Currently this library has 0 external dep (other than go sdk), and supports go 1.6, 1.9, and 1.10 (and later).
// Creating external lib dependencies (plus their transitive dependencies) would make things hard if not impossible.
// We expect under most circumstances, the defaultCap is big enough for any long running services that use this
// library if their xpath regexp cardinality is low. However, in extreme cases when the capacity is reached, we
// simply reset the cache, taking a small subsequent perf hit (next to nothing considering amortization) in trade
// of more complex and less performant LRU type of construct.
type loadingCache struct {
sync.RWMutex
cap int
load loadFunc
m map[interface{}]interface{}
reset int
}
// NewLoadingCache creates a new instance of a loading cache with capacity. Capacity must be >= 0, or
// it will panic. Capacity == 0 means the cache growth is unbounded.
func NewLoadingCache(load loadFunc, capacity int) *loadingCache {
if capacity < 0 {
panic("capacity must be >= 0")
}
return &loadingCache{cap: capacity, load: load, m: make(map[interface{}]interface{})}
}
func (c *loadingCache) get(key interface{}) (interface{}, error) {
c.RLock()
v, found := c.m[key]
c.RUnlock()
if found {
return v, nil
}
v, err := c.load(key)
if err != nil {
return nil, err
}
c.Lock()
if c.cap > 0 && len(c.m) >= c.cap {
c.m = map[interface{}]interface{}{key: v}
c.reset++
} else {
c.m[key] = v
}
c.Unlock()
return v, nil
}
var (
// RegexpCache is a loading cache for string -> *regexp.Regexp mapping. It is exported so that in rare cases
// client can customize load func and/or capacity.
RegexpCache = defaultRegexpCache()
)
func defaultRegexpCache() *loadingCache {
return NewLoadingCache(
func(key interface{}) (interface{}, error) {
return regexp.Compile(key.(string))
}, defaultCap)
}
func getRegexp(pattern string) (*regexp.Regexp, error) {
exp, err := RegexpCache.get(pattern)
if err != nil {
return nil, err
}
return exp.(*regexp.Regexp), nil
}
|
