use instance caching instead of memcache

dash/ui.go

@@ -18,16 +18,18 @@ import (
 	"html/template"
 	"net/http"
 	"sort"
+	"sync"
 	"time"
 
 	"appengine"
 	"appengine/datastore"
-	"appengine/memcache"
 )
 
-const (
-	packageCacheKey    = "packages"
+var (
+	packageCache       []*Package
+	packageCacheTime   time.Time
 	packageCacheExpiry = 1 * time.Hour
+	packageCacheMu     sync.RWMutex
 )
 
 func init() {
@@ -36,6 +38,7 @@ func init() {
 
 func ui(w http.ResponseWriter, r *http.Request) {
 	c := appengine.NewContext(r)
+	d := uiData{Add: r.FormValue("add") == "ok"}
 
 	if path := r.FormValue("path"); path != "" && r.Method == "POST" {
 		if pathOK(path) {
@@ -45,18 +48,18 @@ func ui(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	doCache := r.FormValue("nocache") == ""
-	p, err := packages(c, doCache)
+	var err error
+	if r.FormValue("nocache") == "" {
+		d.Packages, err = cachedPackages(c)
+	} else {
+		d.Packages, err = packages(c)
+	}
 	if err != nil {
 		http.Error(w, "error fetching package list", 500)
 		c.Errorf("packages: %v", err)
 		return
 	}
 
-	d := uiData{
-		Add:      r.FormValue("add") == "ok",
-		Packages: p,
-	}
 	if err := uiTemplate.Execute(w, d); err != nil {
 		c.Errorf("uiTemplate: %v", err)
 	}
@@ -69,29 +72,37 @@ type uiData struct {
 
 var uiTemplate = template.Must(template.ParseFiles("dash/ui.html"))
 
-func packages(c appengine.Context, doCache bool) ([]*Package, error) {
+func cachedPackages(c appengine.Context) ([]*Package, error) {
+	var load bool
 	var pkgs []*Package
-	err := memcache.ErrCacheMiss
-	if doCache {
-		_, err = memcache.Gob.Get(c, packageCacheKey, &pkgs)
+	packageCacheMu.RLock()
+	if packageCache == nil || time.Since(packageCacheTime) > packageCacheExpiry {
+		load = true
+	} else {
+		pkgs = packageCache
 	}
-	if err == memcache.ErrCacheMiss {
-		_, err = datastore.NewQuery("Package").GetAll(c, &pkgs)
-		if err != nil {
-			return nil, err
-		}
-		sort.Sort(packageList(pkgs))
-		if doCache {
-			err = memcache.Gob.Set(c, &memcache.Item{
-				Key:        packageCacheKey,
-				Object:     pkgs,
-				Expiration: packageCacheExpiry,
-			})
-		}
+	packageCacheMu.RUnlock()
+	if !load {
+		return pkgs, nil
 	}
+	packageCacheMu.Lock()
+	defer packageCacheMu.Unlock()
+	pkgs, err := packages(c)
+	if err != nil {
+		return nil, err
+	}
+	packageCache = pkgs
+	packageCacheTime = time.Now()
+	return pkgs, nil
+}
+
+func packages(c appengine.Context) ([]*Package, error) {
+	var pkgs []*Package
+	_, err := datastore.NewQuery("Package").GetAll(c, &pkgs)
 	if err != nil {
 		return nil, err
 	}
+	sort.Sort(packageList(pkgs))
 	return pkgs, nil
 }