restic/internal/fuse/blobcache.go

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package fuse
import (
"sync"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/restic"
"github.com/hashicorp/golang-lru/simplelru"
)
// Crude estimate of the overhead per blob: a SHA-256, a linked list node
// and some pointers. See comment in blobCache.add.
const cacheOverhead = len(restic.ID{}) + 64
// A blobCache is a fixed-size cache of blob contents.
// It is safe for concurrent access.
type blobCache struct {
mu sync.Mutex
c *simplelru.LRU
free, size int // Current and max capacity, in bytes.
}
// Construct a blob cache that stores at most size bytes worth of blobs.
func newBlobCache(size int) *blobCache {
c := &blobCache{
free: size,
size: size,
}
// NewLRU wants us to specify some max. number of entries, else it errors.
// The actual maximum will be smaller than size/cacheOverhead, because we
// evict entries (RemoveOldest in add) to maintain our size bound.
maxEntries := size / cacheOverhead
lru, err := simplelru.NewLRU(maxEntries, c.evict)
if err != nil {
panic(err) // Can only be maxEntries <= 0.
}
c.c = lru
return c
}
func (c *blobCache) add(id restic.ID, blob []byte) {
debug.Log("blobCache: add %v", id)
size := len(blob) + cacheOverhead
if size > c.size {
return
}
c.mu.Lock()
defer c.mu.Unlock()
var key interface{} = id
if c.c.Contains(key) { // Doesn't update the recency list.
return
}
// This loop takes at most min(maxEntries, maxchunksize/cacheOverhead)
// iterations.
for size > c.free {
c.c.RemoveOldest()
}
c.c.Add(key, blob)
c.free -= size
}
func (c *blobCache) get(id restic.ID) ([]byte, bool) {
c.mu.Lock()
value, ok := c.c.Get(id)
c.mu.Unlock()
debug.Log("blobCache: get %v, hit %v", id, ok)
blob, ok := value.([]byte)
return blob, ok
}
func (c *blobCache) evict(key, value interface{}) {
blob := value.([]byte)
debug.Log("blobCache: evict %v, %d bytes", key, len(blob))
c.free += len(blob) + cacheOverhead
}