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173 lines
4.6 KiB
Go
173 lines
4.6 KiB
Go
/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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*/
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// Package objcache implements in memory caching methods.
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package objcache
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import (
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"bytes"
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"errors"
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"io"
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"sync"
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"time"
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)
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// NoExpiration represents caches to be permanent and can only be deleted.
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var NoExpiration = time.Duration(0)
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// Cache holds the required variables to compose an in memory cache system
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// which also provides expiring key mechanism and also maxSize.
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type Cache struct {
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// Mutex is used for handling the concurrent
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// read/write requests for cache
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mutex *sync.RWMutex
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// maxSize is a total size for overall cache
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maxSize uint64
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// currentSize is a current size in memory
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currentSize uint64
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// OnEviction - callback function for eviction
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OnEviction func(a ...interface{})
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// totalEvicted counter to keep track of total expirations
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totalEvicted int
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// map of objectName and its contents
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entries map[string][]byte
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// Expiration in time duration.
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expiry time.Duration
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}
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// New creates an inmemory cache
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//
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// maxSize is used for expiring objects before we run out of memory
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// expiration is used for expiration of a key from cache
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func New(maxSize uint64, expiry time.Duration) *Cache {
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return &Cache{
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mutex: &sync.RWMutex{},
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maxSize: maxSize,
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entries: make(map[string][]byte),
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expiry: expiry,
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}
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}
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// ErrKeyNotFoundInCache - key not found in cache.
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var ErrKeyNotFoundInCache = errors.New("Key not found in cache")
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// ErrCacheFull - cache is full.
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var ErrCacheFull = errors.New("Not enough space in cache")
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// Used for adding entry to the object cache. Implements io.WriteCloser
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type cacheBuffer struct {
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*bytes.Buffer // Implements io.Writer
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onClose func()
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}
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// On close, onClose() is called which checks if all object contents
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// have been written so that it can save the buffer to the cache.
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func (c cacheBuffer) Close() error {
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c.onClose()
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return nil
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}
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// Create - validates if object size fits with in cache size limit and returns a io.WriteCloser
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// to which object contents can be written and finally Close()'d. During Close() we
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// checks if the amount of data written is equal to the size of the object, in which
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// case it saves the contents to object cache.
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func (c *Cache) Create(key string, size int64) (w io.WriteCloser, err error) {
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c.mutex.Lock()
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defer c.mutex.Unlock()
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valueLen := uint64(size)
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if c.maxSize > 0 {
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// Check if the size of the object is not bigger than the capacity of the cache.
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if valueLen > c.maxSize {
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return nil, ErrCacheFull
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}
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// TODO - auto expire random key.
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if c.currentSize+valueLen > c.maxSize {
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return nil, ErrCacheFull
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}
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}
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// Will hold the object contents.
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buf := bytes.NewBuffer(make([]byte, 0, size))
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// Account for the memory allocated above.
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c.currentSize += uint64(size)
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// Function called on close which saves the object contents
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// to the object cache.
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onClose := func() {
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c.mutex.Lock()
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defer c.mutex.Unlock()
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if buf.Len() != int(size) {
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// Full object not available hence do not save buf to object cache.
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c.currentSize -= uint64(size)
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return
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}
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// Full object available in buf, save it to cache.
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c.entries[key] = buf.Bytes()
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return
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}
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// Object contents that is written - cacheBuffer.Write(data)
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// will be accumulated in buf which implements io.Writer.
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return cacheBuffer{
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buf,
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onClose,
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}, nil
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}
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// Open - open the in-memory file, returns an in memory read seeker.
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// returns an error ErrNotFoundInCache, if the key does not exist.
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func (c *Cache) Open(key string) (io.ReadSeeker, error) {
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c.mutex.RLock()
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defer c.mutex.RUnlock()
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// Entry exists, return the readable buffer.
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buffer, ok := c.entries[key]
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if !ok {
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return nil, ErrKeyNotFoundInCache
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}
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return bytes.NewReader(buffer), nil
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}
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// Delete - delete deletes an entry from in-memory fs.
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func (c *Cache) Delete(key string) {
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c.mutex.Lock()
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defer c.mutex.Unlock()
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// Delete an entry.
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buffer, ok := c.entries[key]
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if ok {
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c.deleteEntry(key, int64(len(buffer)))
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}
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}
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// Deletes the entry that was found.
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func (c *Cache) deleteEntry(key string, size int64) {
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delete(c.entries, key)
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c.currentSize -= uint64(size)
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c.totalEvicted++
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if c.OnEviction != nil {
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c.OnEviction(key)
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}
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}
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