Revert "trie: make fullnode children hash calculation concurrently (#15131)" (#15889)

This reverts commit 0f7fbb85d6e939510a3e3bb6493a9a332ddfd8e8.

3 files changed, 32 insertions, 88 deletions

diff --git a/trie/hasher.go b/trie/hasher.go
index 5186d7669..4719aabf6 100644
--- a/trie/hasher.go
+++ b/trie/hasher.go
@@ -26,46 +26,27 @@ import (
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
-// calculator is a utility used by the hasher to calculate the hash value of the tree node.
-type calculator struct {
-	sha    hash.Hash
-	buffer *bytes.Buffer
+type hasher struct {
+	tmp                  *bytes.Buffer
+	sha                  hash.Hash
+	cachegen, cachelimit uint16
 }
 
-// calculatorPool is a set of temporary calculators that may be individually saved and retrieved.
-var calculatorPool = sync.Pool{
+// hashers live in a global pool.
+var hasherPool = sync.Pool{
 	New: func() interface{} {
-		return &calculator{buffer: new(bytes.Buffer), sha: sha3.NewKeccak256()}
+		return &hasher{tmp: new(bytes.Buffer), sha: sha3.NewKeccak256()}
 	},
 }
 
-// hasher hasher is used to calculate the hash value of the whole tree.
-type hasher struct {
-	cachegen   uint16
-	cachelimit uint16
-	threaded   bool
-	mu         sync.Mutex
-}
-
 func newHasher(cachegen, cachelimit uint16) *hasher {
-	h := &hasher{
-		cachegen:   cachegen,
-		cachelimit: cachelimit,
-	}
+	h := hasherPool.Get().(*hasher)
+	h.cachegen, h.cachelimit = cachegen, cachelimit
 	return h
 }
 
-// newCalculator retrieves a cleaned calculator from calculator pool.
-func (h *hasher) newCalculator() *calculator {
-	calculator := calculatorPool.Get().(*calculator)
-	calculator.buffer.Reset()
-	calculator.sha.Reset()
-	return calculator
-}
-
-// returnCalculator returns a no longer used calculator to the pool.
-func (h *hasher) returnCalculator(calculator *calculator) {
-	calculatorPool.Put(calculator)
+func returnHasherToPool(h *hasher) {
+	hasherPool.Put(h)
 }
 
 // hash collapses a node down into a hash node, also returning a copy of the
@@ -142,49 +123,16 @@ func (h *hasher) hashChildren(original node, db DatabaseWriter) (node, node, err
 		// Hash the full node's children, caching the newly hashed subtrees
 		collapsed, cached := n.copy(), n.copy()
 
-		// hashChild is a helper to hash a single child, which is called either on the
-		// same thread as the caller or in a goroutine for the toplevel branching.
-		hashChild := func(index int, wg *sync.WaitGroup) {
-			if wg != nil {
-				defer wg.Done()
-			}
-			// Ensure that nil children are encoded as empty strings.
-			if collapsed.Children[index] == nil {
-				collapsed.Children[index] = valueNode(nil)
-				return
-			}
-			// Hash all other children properly
-			var herr error
-			collapsed.Children[index], cached.Children[index], herr = h.hash(n.Children[index], db, false)
-			if herr != nil {
-				h.mu.Lock() // rarely if ever locked, no congenstion
-				err = herr
-				h.mu.Unlock()
+		for i := 0; i < 16; i++ {
+			if n.Children[i] != nil {
+				collapsed.Children[i], cached.Children[i], err = h.hash(n.Children[i], db, false)
+				if err != nil {
+					return original, original, err
+				}
+			} else {
+				collapsed.Children[i] = valueNode(nil) // Ensure that nil children are encoded as empty strings.
 			}
 		}
-		// If we're not running in threaded mode yet, span a goroutine for each child
-		if !h.threaded {
-			// Disable further threading
-			h.threaded = true
-
-			// Hash all the children concurrently
-			var wg sync.WaitGroup
-			for i := 0; i < 16; i++ {
-				wg.Add(1)
-				go hashChild(i, &wg)
-			}
-			wg.Wait()
-
-			// Reenable threading for subsequent hash calls
-			h.threaded = false
-		} else {
-			for i := 0; i < 16; i++ {
-				hashChild(i, nil)
-			}
-		}
-		if err != nil {
-			return original, original, err
-		}
 		cached.Children[16] = n.Children[16]
 		if collapsed.Children[16] == nil {
 			collapsed.Children[16] = valueNode(nil)
@@ -202,29 +150,24 @@ func (h *hasher) store(n node, db DatabaseWriter, force bool) (node, error) {
 	if _, isHash := n.(hashNode); n == nil || isHash {
 		return n, nil
 	}
-	calculator := h.newCalculator()
-	defer h.returnCalculator(calculator)
-
 	// Generate the RLP encoding of the node
-	if err := rlp.Encode(calculator.buffer, n); err != nil {
+	h.tmp.Reset()
+	if err := rlp.Encode(h.tmp, n); err != nil {
 		panic("encode error: " + err.Error())
 	}
-	if calculator.buffer.Len() < 32 && !force {
+
+	if h.tmp.Len() < 32 && !force {
 		return n, nil // Nodes smaller than 32 bytes are stored inside their parent
 	}
 	// Larger nodes are replaced by their hash and stored in the database.
 	hash, _ := n.cache()
 	if hash == nil {
-		calculator.sha.Write(calculator.buffer.Bytes())
-		hash = hashNode(calculator.sha.Sum(nil))
+		h.sha.Reset()
+		h.sha.Write(h.tmp.Bytes())
+		hash = hashNode(h.sha.Sum(nil))
 	}
 	if db != nil {
-		// db might be a leveldb batch, which is not safe for concurrent writes
-		h.mu.Lock()
-		err := db.Put(hash, calculator.buffer.Bytes())
-		h.mu.Unlock()
-
-		return hash, err
+		return hash, db.Put(hash, h.tmp.Bytes())
 	}
 	return hash, nil
 }
diff --git a/trie/secure_trie.go b/trie/secure_trie.go
index 1fde45165..20c303f31 100644
--- a/trie/secure_trie.go
+++ b/trie/secure_trie.go
@@ -199,10 +199,10 @@ func (t *SecureTrie) secKey(key []byte) []byte {
 // invalid on the next call to hashKey or secKey.
 func (t *SecureTrie) hashKey(key []byte) []byte {
 	h := newHasher(0, 0)
-	calculator := h.newCalculator()
-	calculator.sha.Write(key)
-	buf := calculator.sha.Sum(t.hashKeyBuf[:0])
-	h.returnCalculator(calculator)
+	h.sha.Reset()
+	h.sha.Write(key)
+	buf := h.sha.Sum(t.hashKeyBuf[:0])
+	returnHasherToPool(h)
 	return buf
 }
 
diff --git a/trie/trie.go b/trie/trie.go
index 7c1b5e1b6..8fe98d835 100644
--- a/trie/trie.go
+++ b/trie/trie.go
@@ -501,5 +501,6 @@ func (t *Trie) hashRoot(db DatabaseWriter) (node, node, error) {
 		return hashNode(emptyRoot.Bytes()), nil, nil
 	}
 	h := newHasher(t.cachegen, t.cachelimit)
+	defer returnHasherToPool(h)
 	return h.hash(t.root, db, true)
 }