1 files changed, 84 insertions, 0 deletions
diff --git a/cache/namedmemcache/named_cache.go b/cache/namedmemcache/named_cache.go
new file mode 100644
index 000000000..18fbea391
--- /dev/null
+++ b/cache/namedmemcache/named_cache.go
@@ -0,0 +1,84 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package namedmemcache provides a memory cache with a named lock. This is suitable
+// for situations where creating the cached resource can be time consuming or otherwise
+// resource hungry, or in situations where a "once only per key" is a requirement.
+package namedmemcache
+
+import (
+	"sync"
+
+	"github.com/BurntSushi/locker"
+)
+
+// Cache holds the cached values.
+type Cache struct {
+	nlocker *locker.Locker
+	cache   map[string]cacheEntry
+	mu      sync.RWMutex
+}
+
+type cacheEntry struct {
+	value interface{}
+	err   error
+}
+
+// New creates a new cache.
+func New() *Cache {
+	return &Cache{
+		nlocker: locker.NewLocker(),
+		cache:   make(map[string]cacheEntry),
+	}
+}
+
+// Clear clears the cache state.
+func (c *Cache) Clear() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	c.cache = make(map[string]cacheEntry)
+	c.nlocker = locker.NewLocker()
+
+}
+
+// GetOrCreate tries to get the value with the given cache key, if not found
+// create will be called and cached.
+// This method is thread safe. It also guarantees that the create func for a given
+// key is invoced only once for this cache.
+func (c *Cache) GetOrCreate(key string, create func() (interface{}, error)) (interface{}, error) {
+	c.mu.RLock()
+	entry, found := c.cache[key]
+	c.mu.RUnlock()
+
+	if found {
+		return entry.value, entry.err
+	}
+
+	c.nlocker.Lock(key)
+	defer c.nlocker.Unlock(key)
+
+	// Double check
+	if entry, found := c.cache[key]; found {
+		return entry.value, entry.err
+	}
+
+	// Create it.
+	value, err := create()
+
+	c.mu.Lock()
+	c.cache[key] = cacheEntry{value: value, err: err}
+	c.mu.Unlock()
+
+	return value, err
+}