LogDog: Add Storage-layer data caching.

logdog/common/storage/memory/cache.go

Index: logdog/common/storage/memory/cache.go
diff --git a/logdog/common/storage/memory/cache.go b/logdog/common/storage/memory/cache.go
new file mode 100644
index 0000000000000000000000000000000000000000..863ff897a718b4e0d09329c3b6efb0d8765462b8
--- /dev/null
+++ b/logdog/common/storage/memory/cache.go
@@ -0,0 +1,68 @@
+// 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 memory
+
+import (
+	"sync"
+	"time"
+
+	"github.com/luci/luci-go/logdog/common/storage/caching"
+
+	"golang.org/x/net/context"
+)
+
+// Cache is an in-memory caching.Cache implementation.
+type Cache struct {
+	mu       sync.Mutex
+	cacheMap map[cacheKey]caching.Item
+}
+
+var _ caching.Cache = (*Cache)(nil)
+
+type cacheKey struct {
+	schema string
+	typ    string
+	key    string
+}
+
+// Put implements caching.Cache.
+func (c *Cache) Put(ctx context.Context, exp time.Duration, items ...*caching.Item) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.cacheMap == nil {
+		c.cacheMap = make(map[cacheKey]caching.Item)
+	}
+
+	for _, itm := range items {
+		c.cacheMap[c.keyForItem(itm)] = *itm
+	}
+}
+
+// Get implements caching.Cache.
+func (c *Cache) Get(ctx context.Context, items ...*caching.Item) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	for _, itm := range items {
+		if cacheItem, ok := c.cacheMap[c.keyForItem(itm)]; ok {
+			itm.Data = append([]byte{}, cacheItem.Data...)
+		} else {
+			itm.Data = nil
+		}
+	}
+}
+
+// Delete deletes a set of keys from the cache.
+func (c *Cache) Delete(schema, typ string, key ...string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	for _, k := range key {
+		delete(c.cacheMap, cacheKey{schema, typ, k})
+	}
+}
+
+func (*Cache) keyForItem(itm *caching.Item) cacheKey { return cacheKey{itm.Schema, itm.Type, itm.Key} }