1 files changed, 82 insertions, 0 deletions
diff --git a/misc/dashboard/app/cache/cache.go b/misc/dashboard/app/cache/cache.go
new file mode 100644
index 000000000..d290ed416
--- /dev/null
+++ b/misc/dashboard/app/cache/cache.go
@@ -0,0 +1,82 @@
+// 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"
+	"http"
+	"time"
+
+	"appengine"
+	"appengine/memcache"
+)
+
+const (
+	nocache = "nocache"
+	timeKey = "cachetime"
+	expiry  = 600 // 10 minutes
+)
+
+func newTime() uint64 { return uint64(time.Seconds()) << 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)
+	}
+}