fix(arc): striped locking on last byte of CID

- fixes #64

arc_cache.go

@@ -2,6 +2,7 @@ package blockstore
 
 import (
 	"context"
+	"sync"
 
 	lru "github.com/hashicorp/golang-lru"
 	blocks "github.com/ipfs/go-block-format"
@@ -17,7 +18,9 @@ type cacheSize int
 // size. This provides block access-time improvements, allowing
 // to short-cut many searches without querying the underlying datastore.
 type arccache struct {
-	cache      *lru.TwoQueueCache
+	cache *lru.TwoQueueCache
+	lks   [256]sync.Mutex
+
 	blockstore Blockstore
 	viewer     Viewer
 
@@ -33,7 +36,7 @@ func newARCCachedBS(ctx context.Context, bs Blockstore, lruSize int) (*arccache,
 	if err != nil {
 		return nil, err
 	}
-	c := &arccache{cache: cache, blockstore: bs}
+	c := &arccache{cache: cache, lks: [256]sync.Mutex{}, blockstore: bs}
 	c.hits = metrics.NewCtx(ctx, "arc.hits_total", "Number of ARC cache hits").Counter()
 	c.total = metrics.NewCtx(ctx, "arc_total", "Total number of ARC cache requests").Counter()
 	if v, ok := bs.(Viewer); ok {
@@ -47,6 +50,9 @@ func (b *arccache) DeleteBlock(k cid.Cid) error {
 		return nil
 	}
 
+	b.lks[k.Bytes()[len(k.Bytes())-1]].Lock()
+	defer b.lks[k.Bytes()[len(k.Bytes())-1]].Unlock()
+
 	b.cache.Remove(k) // Invalidate cache before deleting.
 	err := b.blockstore.DeleteBlock(k)
 	if err == nil {
@@ -59,6 +65,7 @@ func (b *arccache) Has(k cid.Cid) (bool, error) {
 	if has, _, ok := b.queryCache(k); ok {
 		return has, nil
 	}
+
 	has, err := b.blockstore.Has(k)
 	if err != nil {
 		return false, err
@@ -79,6 +86,10 @@ func (b *arccache) GetSize(k cid.Cid) (int, error) {
 		}
 		// we have it but don't know the size, ask the datastore.
 	}
+
+	b.lks[k.Bytes()[len(k.Bytes())-1]].Lock()
+	defer b.lks[k.Bytes()[len(k.Bytes())-1]].Unlock()
+
 	blockSize, err := b.blockstore.GetSize(k)
 	if err == ErrNotFound {
 		b.cacheHave(k, false)
@@ -123,6 +134,9 @@ func (b *arccache) Get(k cid.Cid) (blocks.Block, error) {
 		return nil, ErrNotFound
 	}
 
+	b.lks[k.Bytes()[len(k.Bytes())-1]].Lock()
+	defer b.lks[k.Bytes()[len(k.Bytes())-1]].Unlock()
+
 	bl, err := b.blockstore.Get(k)
 	if bl == nil && err == ErrNotFound {
 		b.cacheHave(k, false)
@@ -137,6 +151,9 @@ func (b *arccache) Put(bl blocks.Block) error {
 		return nil
 	}
 
+	b.lks[bl.Cid().Bytes()[len(bl.Cid().Bytes())-1]].Lock()
+	defer b.lks[bl.Cid().Bytes()[len(bl.Cid().Bytes())-1]].Unlock()
+
 	err := b.blockstore.Put(bl)
 	if err == nil {
 		b.cacheSize(bl.Cid(), len(bl.RawData()))
@@ -151,8 +168,16 @@ func (b *arccache) PutMany(bs []blocks.Block) error {
 		// the block isn't in storage
 		if has, _, ok := b.queryCache(block.Cid()); !ok || (ok && !has) {
 			good = append(good, block)
+			b.lks[block.Cid().Bytes()[len(block.Cid().Bytes())-1]].Lock()
 		}
 	}
+
+	defer func() {
+		for _, block := range good {
+			b.lks[block.Cid().Bytes()[len(block.Cid().Bytes())-1]].Unlock()
+		}
+	}()
+
 	err := b.blockstore.PutMany(good)
 	if err != nil {
 		return err