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// Copyright 2015 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 hugolib
import (
"sync"
)
type pageCache struct {
sync.RWMutex
m map[string][][2]Pages
}
func newPageCache() *pageCache {
return &pageCache{m: make(map[string][][2]Pages)}
}
// get gets a Pages slice from the cache matching the given key and Pages slice.
// If none found in cache, a copy of the supplied slice is created.
//
// If an apply func is provided, that func is applied to the newly created copy.
//
// The cache and the execution of the apply func is protected by a RWMutex.
func (c *pageCache) get(key string, p Pages, apply func(p Pages)) (Pages, bool) {
c.RLock()
if cached, ok := c.m[key]; ok {
for _, ps := range cached {
if probablyEqualPages(p, ps[0]) {
c.RUnlock()
return ps[1], true
}
}
}
c.RUnlock()
c.Lock()
defer c.Unlock()
// double-check
if cached, ok := c.m[key]; ok {
for _, ps := range cached {
if probablyEqualPages(p, ps[0]) {
return ps[1], true
}
}
}
pagesCopy := append(Pages(nil), p...)
if apply != nil {
apply(pagesCopy)
}
if v, ok := c.m[key]; ok {
c.m[key] = append(v, [2]Pages{p, pagesCopy})
} else {
c.m[key] = [][2]Pages{{p, pagesCopy}}
}
return pagesCopy, false
}
// "probably" as in: we do not compare every element for big slices, but that is
// good enough for our use case.
// TODO(bep) there is a similar method in pagination.go. DRY.
func probablyEqualPages(p1, p2 Pages) bool {
if p1 == nil && p2 == nil {
return true
}
if p1 == nil || p2 == nil {
return false
}
if p1.Len() != p2.Len() {
return false
}
if p1.Len() == 0 {
return true
}
step := 1
if len(p1) >= 50 {
step = len(p1) / 10
}
for i := 0; i < len(p1); i += step {
if p1[i] != p2[i] {
return false
}
}
return true
}
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