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
|
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package cache
import (
"fmt"
"net/http"
"time"
"appengine"
"appengine/memcache"
)
const (
nocache = "nocache"
timeKey = "cachetime"
expiry = 600 // 10 minutes
)
func newTime() uint64 { return uint64(time.Now().Unix()) << 32 }
// Now returns the current logical datastore time to use for cache lookups.
func Now(c appengine.Context) uint64 {
t, err := memcache.Increment(c, timeKey, 0, newTime())
if err != nil {
c.Errorf("cache.Now: %v", err)
return 0
}
return t
}
// Tick sets the current logical datastore time to a never-before-used time
// and returns that time. It should be called to invalidate the cache.
func Tick(c appengine.Context) uint64 {
t, err := memcache.Increment(c, timeKey, 1, newTime())
if err != nil {
c.Errorf("cache.Tick: %v", err)
return 0
}
return t
}
// Get fetches data for name at time now from memcache and unmarshals it into
// value. It reports whether it found the cache record and logs any errors to
// the admin console.
func Get(r *http.Request, now uint64, name string, value interface{}) bool {
if now == 0 || r.FormValue(nocache) != "" {
return false
}
c := appengine.NewContext(r)
key := fmt.Sprintf("%s.%d", name, now)
_, err := memcache.JSON.Get(c, key, value)
if err == nil {
c.Debugf("cache hit %q", key)
return true
}
c.Debugf("cache miss %q", key)
if err != memcache.ErrCacheMiss {
c.Errorf("get cache %q: %v", key, err)
}
return false
}
// Set puts value into memcache under name at time now.
// It logs any errors to the admin console.
func Set(r *http.Request, now uint64, name string, value interface{}) {
if now == 0 || r.FormValue(nocache) != "" {
return
}
c := appengine.NewContext(r)
key := fmt.Sprintf("%s.%d", name, now)
err := memcache.JSON.Set(c, &memcache.Item{
Key: key,
Object: value,
Expiration: expiry,
})
if err != nil {
c.Errorf("set cache %q: %v", key, err)
}
}
|
