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// Copyright 2014 Google Inc. 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 filecache provides a LRU cache of open os.File objects, closing old
// files as new ones are opened.
package filecache
import (
"fmt"
"os"
"sync"
"time"
"github.com/google/stenographer/base"
)
var v = base.V
type CachedFile struct {
cache *Cache
// protected by cache.mu
at time.Time
prev, next *CachedFile
mu sync.RWMutex
// protected by mu
filename string
f *os.File
}
func NewCache(maxOpened int) *Cache {
if maxOpened < 1 {
panic("maxOpened must be > 0")
}
return &Cache{maxOpened: maxOpened}
}
type Cache struct {
mu sync.Mutex
first, last *CachedFile
opened, maxOpened int
}
func (cf *CachedFile) moveToFront() {
cf.at = time.Now()
if cf.cache.first == cf {
return
}
// Remove from current place in list
if cf.prev != nil {
cf.prev.next = cf.next
}
if cf.next != nil {
cf.next.prev = cf.prev
}
// Update last element in list, if necessary
if cf.cache.last == nil {
cf.cache.last = cf
} else if cf.cache.last == cf {
cf.cache.last = cf.prev
}
// Update first element in list
if cf.cache.first != nil {
cf.next = cf.cache.first
cf.cache.first.prev = cf
}
cf.cache.first = cf
cf.prev = nil
}
func (c *Cache) Open(filename string) *CachedFile {
v(3, "Deferring open of %q", filename)
return &CachedFile{cache: c, filename: filename}
}
func (cf *CachedFile) readLockedFile() error {
cf.cache.mu.Lock()
cf.moveToFront()
cf.cache.mu.Unlock()
for {
cf.mu.RLock()
if cf.f != nil {
return nil
}
cf.mu.RUnlock()
if err := cf.openFile(); err != nil {
return fmt.Errorf("lazily opening: %v", err)
}
}
}
func (cf *CachedFile) ReadAt(p []byte, off int64) (int, error) {
if err := cf.readLockedFile(); err != nil {
return 0, err
}
defer cf.mu.RUnlock()
return cf.f.ReadAt(p, off)
}
func (cf *CachedFile) Read(p []byte) (int, error) {
if err := cf.readLockedFile(); err != nil {
return 0, err
}
defer cf.mu.RUnlock()
return cf.f.Read(p)
}
func (cf *CachedFile) Stat() (os.FileInfo, error) {
if err := cf.readLockedFile(); err != nil {
return nil, err
}
defer cf.mu.RUnlock()
return cf.f.Stat()
}
func (cf *CachedFile) Write(p []byte) (int, error) {
return 0, fmt.Errorf("cached file not writable")
}
func (cf *CachedFile) Sync() error {
return fmt.Errorf("cached file not syncable")
}
func (cf *CachedFile) openFile() error {
cf.cache.mu.Lock()
defer cf.cache.mu.Unlock()
cf.mu.Lock()
defer cf.mu.Unlock()
if cf.f != nil {
return nil
}
v(2, "Opening %q", cf.filename)
newF, err := os.Open(cf.filename)
if err != nil {
v(1, "Open of %q failed: %v", cf.filename, err)
return err
}
cf.f = newF
cf.moveToFront()
cf.cache.opened++
for cf.cache.opened > cf.cache.maxOpened {
v(3, "Cached files above max, closing last")
oldLast := cf.cache.last
cf.cache.last = oldLast.prev
if cf.cache.last != nil {
cf.cache.last.next = nil
}
oldLast.prev = nil
oldLast.next = nil
oldLast.closeFile()
}
return nil
}
func (cf *CachedFile) Close() error {
// Remove me from the cache, so others can't reference me
cf.cache.mu.Lock()
defer cf.cache.mu.Unlock()
cf.mu.Lock()
defer cf.mu.Unlock()
return cf.closeFile()
}
func (cf *CachedFile) closeFile() error {
if cf.f == nil {
v(3, "Close of already-closed file %q ignored", cf.filename)
return nil
}
v(2, "Closing %q", cf.filename)
cf.cache.opened--
f := cf.f
cf.f = nil
return f.Close()
}
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