server/config: Generic caching backend.

luci_config/server/cfgclient/backend/caching/proccache.go

+// 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 caching
+
+import (
+        "strings"
+        "time"
+
+        "github.com/luci/luci-go/common/data/caching/proccache"
+        "github.com/luci/luci-go/luci_config/server/cfgclient/backend"
+
+        "golang.org/x/net/context"
+)
+
+// ProcCache returns a backend.B that caches configuration service results in an
+// in-memory proccache instance.
+//
+// This will only cache results for AsService calls; any other Authority will
+// pass through.
+func ProcCache(b backend.B, exp time.Duration) backend.B {
+        return &Backend{
+                B: b,
+                CacheGet: func(c context.Context, key Key, l Loader) (*Value, error) {
+                        if key.Authority != backend.AsService {
+                                return l(c, key, nil)
+                        }
+
+                        k := mkProcCacheKey(&key)
+                        ret, err := proccache.GetOrMake(c, k, func() (interface{}, time.Duration, error) {
+                                v, err := l(c, key, nil)
+                                if err != nil {
+                                        return nil, 0, err
+                                }
+                                return v, exp, nil
+                        })
+                        if err != nil {
+                                return nil, err
+                        }
+                        return ret.(*Value), nil
+                },
+        }
+}
+
+type procCacheKey string
+
+func mkProcCacheKey(key *Key) procCacheKey {
+        return procCacheKey(strings.Join([]string{
+                key.Schema,
+                string(key.Op),
+                key.ConfigSet,
+                key.Path,
+                string(key.GetAllTarget),
+        }, ":"))
+}