LogDog: Add Storage-layer data caching.

logdog/appengine/coordinator/coordinatorTest/storage_cache.go

Index: logdog/appengine/coordinator/coordinatorTest/storage_cache.go
diff --git a/logdog/appengine/coordinator/coordinatorTest/storage_cache.go b/logdog/appengine/coordinator/coordinatorTest/storage_cache.go
new file mode 100644
index 0000000000000000000000000000000000000000..594cbef4c0df5a92820d5c035bf826034b050b21
--- /dev/null
+++ b/logdog/appengine/coordinator/coordinatorTest/storage_cache.go
@@ -0,0 +1,70 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package coordinatorTest
+
+import (
+	"sync"
+	"time"
+
+	"github.com/luci/luci-go/logdog/common/storage/caching"
+
+	"golang.org/x/net/context"
+)
+
+// StorageCache wraps the default storage cache instance, adding tracking
+// information that is useful for testing.
+type StorageCache struct {
+	Base caching.Cache
+
+	statsMu sync.Mutex
+	stats   StorageCacheStats
+}
+
+// StorageCacheStats expose stats for a StorageCache instance.
+type StorageCacheStats struct {
+	Puts   int
+	Hits   int
+	Misses int
+}
+
+// Clear clears the stats for this cache instance.
+func (sc *StorageCache) Clear() {
+	sc.statsMu.Lock()
+	defer sc.statsMu.Unlock()
+	sc.stats = StorageCacheStats{}
+}
+
+// Stats returns the stats for this cache instance.
+func (sc *StorageCache) Stats() StorageCacheStats {
+	sc.statsMu.Lock()
+	defer sc.statsMu.Unlock()
+	return sc.stats
+}
+
+// Get implements caching.Cache.
+func (sc *StorageCache) Get(c context.Context, items ...*caching.Item) {
+	sc.Base.Get(c, items...)
+
+	// Calculate our hit/misses from the result.
+	sc.statsMu.Lock()
+	defer sc.statsMu.Unlock()
+	for _, it := range items {
+		if it.Data != nil {
+			sc.stats.Hits++
+		} else {
+			sc.stats.Misses++
+		}
+	}
+
+}
+
+// Put implements caching.Cache.
+func (sc *StorageCache) Put(c context.Context, exp time.Duration, items ...*caching.Item) {
+	sc.Base.Put(c, exp, items...)
+
+	sc.statsMu.Lock()
+	defer sc.statsMu.Unlock()
+	sc.stats.Puts += len(items)
+}