minio/pkg/objcache/objcache.go

173 lines
4.6 KiB
Go

/*
* Minio Cloud Storage, (C) 2016 Minio, Inc.
*
* 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 objcache implements in memory caching methods.
package objcache
import (
"bytes"
"errors"
"io"
"sync"
"time"
)
// NoExpiration represents caches to be permanent and can only be deleted.
var NoExpiration = time.Duration(0)
// Cache holds the required variables to compose an in memory cache system
// which also provides expiring key mechanism and also maxSize.
type Cache struct {
// Mutex is used for handling the concurrent
// read/write requests for cache
mutex *sync.RWMutex
// maxSize is a total size for overall cache
maxSize uint64
// currentSize is a current size in memory
currentSize uint64
// OnEviction - callback function for eviction
OnEviction func(a ...interface{})
// totalEvicted counter to keep track of total expirations
totalEvicted int
// map of objectName and its contents
entries map[string][]byte
// Expiration in time duration.
expiry time.Duration
}
// New creates an inmemory cache
//
// maxSize is used for expiring objects before we run out of memory
// expiration is used for expiration of a key from cache
func New(maxSize uint64, expiry time.Duration) *Cache {
return &Cache{
mutex: &sync.RWMutex{},
maxSize: maxSize,
entries: make(map[string][]byte),
expiry: expiry,
}
}
// ErrKeyNotFoundInCache - key not found in cache.
var ErrKeyNotFoundInCache = errors.New("Key not found in cache")
// ErrCacheFull - cache is full.
var ErrCacheFull = errors.New("Not enough space in cache")
// Used for adding entry to the object cache. Implements io.WriteCloser
type cacheBuffer struct {
*bytes.Buffer // Implements io.Writer
onClose func()
}
// On close, onClose() is called which checks if all object contents
// have been written so that it can save the buffer to the cache.
func (c cacheBuffer) Close() error {
c.onClose()
return nil
}
// Create - validates if object size fits with in cache size limit and returns a io.WriteCloser
// to which object contents can be written and finally Close()'d. During Close() we
// checks if the amount of data written is equal to the size of the object, in which
// case it saves the contents to object cache.
func (c *Cache) Create(key string, size int64) (w io.WriteCloser, err error) {
c.mutex.Lock()
defer c.mutex.Unlock()
valueLen := uint64(size)
if c.maxSize > 0 {
// Check if the size of the object is not bigger than the capacity of the cache.
if valueLen > c.maxSize {
return nil, ErrCacheFull
}
// TODO - auto expire random key.
if c.currentSize+valueLen > c.maxSize {
return nil, ErrCacheFull
}
}
// Will hold the object contents.
buf := bytes.NewBuffer(make([]byte, 0, size))
// Account for the memory allocated above.
c.currentSize += uint64(size)
// Function called on close which saves the object contents
// to the object cache.
onClose := func() {
c.mutex.Lock()
defer c.mutex.Unlock()
if buf.Len() != int(size) {
// Full object not available hence do not save buf to object cache.
c.currentSize -= uint64(size)
return
}
// Full object available in buf, save it to cache.
c.entries[key] = buf.Bytes()
return
}
// Object contents that is written - cacheBuffer.Write(data)
// will be accumulated in buf which implements io.Writer.
return cacheBuffer{
buf,
onClose,
}, nil
}
// Open - open the in-memory file, returns an in memory read seeker.
// returns an error ErrNotFoundInCache, if the key does not exist.
func (c *Cache) Open(key string) (io.ReadSeeker, error) {
c.mutex.RLock()
defer c.mutex.RUnlock()
// Entry exists, return the readable buffer.
buffer, ok := c.entries[key]
if !ok {
return nil, ErrKeyNotFoundInCache
}
return bytes.NewReader(buffer), nil
}
// Delete - delete deletes an entry from in-memory fs.
func (c *Cache) Delete(key string) {
c.mutex.Lock()
defer c.mutex.Unlock()
// Delete an entry.
buffer, ok := c.entries[key]
if ok {
c.deleteEntry(key, int64(len(buffer)))
}
}
// Deletes the entry that was found.
func (c *Cache) deleteEntry(key string, size int64) {
delete(c.entries, key)
c.currentSize -= uint64(size)
c.totalEvicted++
if c.OnEviction != nil {
c.OnEviction(key)
}
}