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.RWMutex
+
 	blockstore Blockstore
 	viewer     Viewer
 
@@ -42,11 +45,32 @@ func newARCCachedBS(ctx context.Context, bs Blockstore, lruSize int) (*arccache,
 	return c, nil
 }
 
+func (b *arccache) rLock(k cid.Cid) func() {
+	b.lks[k.KeyString()[len(k.KeyString())-1]].RLock()
+	return func() {
+		b.lks[k.KeyString()[len(k.KeyString())-1]].RUnlock()
+	}
+}
+
+func (b *arccache) wLock(k cid.Cid) func() {
+	b.lks[k.KeyString()[len(k.KeyString())-1]].Lock()
+	return func() {
+		b.lks[k.KeyString()[len(k.KeyString())-1]].Unlock()
+	}
+}
+
 func (b *arccache) DeleteBlock(k cid.Cid) error {
+	if !k.Defined() {
+		return ErrNotFound
+	}
+
 	if has, _, ok := b.queryCache(k); ok && !has {
 		return nil
 	}
 
+	unlock := b.wLock(k)
+	defer unlock()
+
 	b.cache.Remove(k) // Invalidate cache before deleting.
 	err := b.blockstore.DeleteBlock(k)
 	if err == nil {
@@ -56,9 +80,17 @@ func (b *arccache) DeleteBlock(k cid.Cid) error {
 }
 
 func (b *arccache) Has(k cid.Cid) (bool, error) {
+	if !k.Defined() {
+		return false, ErrNotFound
+	}
+
 	if has, _, ok := b.queryCache(k); ok {
 		return has, nil
 	}
+
+	unlock := b.rLock(k)
+	defer unlock()
+
 	has, err := b.blockstore.Has(k)
 	if err != nil {
 		return false, err
@@ -68,6 +100,10 @@ func (b *arccache) Has(k cid.Cid) (bool, error) {
 }
 
 func (b *arccache) GetSize(k cid.Cid) (int, error) {
+	if !k.Defined() {
+		return -1, ErrNotFound
+	}
+
 	if has, blockSize, ok := b.queryCache(k); ok {
 		if !has {
 			// don't have it, return
@@ -79,6 +115,10 @@ func (b *arccache) GetSize(k cid.Cid) (int, error) {
 		}
 		// we have it but don't know the size, ask the datastore.
 	}
+
+	unlock := b.rLock(k)
+	defer unlock()
+
 	blockSize, err := b.blockstore.GetSize(k)
 	if err == ErrNotFound {
 		b.cacheHave(k, false)
@@ -100,7 +140,6 @@ func (b *arccache) View(k cid.Cid, callback func([]byte) error) error {
 	}
 
 	if !k.Defined() {
-		log.Error("undefined cid in arc cache")
 		return ErrNotFound
 	}
 
@@ -110,19 +149,24 @@ func (b *arccache) View(k cid.Cid, callback func([]byte) error) error {
 		return ErrNotFound
 	}
 
+	unlock := b.rLock(k)
+	defer unlock()
+
 	return b.viewer.View(k, callback)
 }
 
 func (b *arccache) Get(k cid.Cid) (blocks.Block, error) {
 	if !k.Defined() {
-		log.Error("undefined cid in arc cache")
 		return nil, ErrNotFound
 	}
 
 	if has, _, ok := b.queryCache(k); ok && !has {
 		return nil, ErrNotFound
 	}
 
+	unlock := b.rLock(k)
+	defer unlock()
+
 	bl, err := b.blockstore.Get(k)
 	if bl == nil && err == ErrNotFound {
 		b.cacheHave(k, false)
@@ -137,6 +181,9 @@ func (b *arccache) Put(bl blocks.Block) error {
 		return nil
 	}
 
+	unlock := b.wLock(bl.Cid())
+	defer unlock()
+
 	err := b.blockstore.Put(bl)
 	if err == nil {
 		b.cacheSize(bl.Cid(), len(bl.RawData()))
@@ -145,20 +192,35 @@ func (b *arccache) Put(bl blocks.Block) error {
 }
 
 func (b *arccache) PutMany(bs []blocks.Block) error {
+	mxs := [256]*sync.Mutex{}
 	var good []blocks.Block
 	for _, block := range bs {
 		// call put on block if result is inconclusive or we are sure that
 		// the block isn't in storage
 		if has, _, ok := b.queryCache(block.Cid()); !ok || (ok && !has) {
+			if !block.Cid().Defined() {
+				log.Error("undefined cid in arc cache")
+				continue
+			}
+
 			good = append(good, block)
+			mxs[block.Cid().KeyString()[len(block.Cid().KeyString())-1]] = &sync.Mutex{}
 		}
 	}
+
+	for _, mx := range mxs {
+		if mx != nil {
+			mx.Lock()
+		}
+	}
+
 	err := b.blockstore.PutMany(good)
 	if err != nil {
 		return err
 	}
 	for _, block := range good {
 		b.cacheSize(block.Cid(), len(block.RawData()))
+		mxs[block.Cid().KeyString()[len(block.Cid().KeyString())-1]].Unlock()
 	}
 	return nil
 }