triedb/pathdb: parallelize add layer

triedb/pathdb/lookup.go

@@ -18,10 +18,12 @@ package pathdb
 
 import (
 	"fmt"
+	"runtime"
 	"sync"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
+	"golang.org/x/sync/errgroup"
 )
 
 // slicePool is a shared pool of hash slice, for reducing the GC pressure.
@@ -105,24 +107,34 @@ func (l *lookup) addLayer(diff *diffLayer) {
 		lookupAddLayerTimer.UpdateSince(now)
 	}(time.Now())
 
-	// TODO(rjl493456442) theoretically the code below could be parallelized,
-	// but it will slow down the other parts of system (e.g., EVM execution)
-	// with unknown reasons.
-	state := diff.rootHash()
+	var (
+		state   = diff.rootHash()
+		lock    sync.Mutex
+		workers errgroup.Group
+	)
+	workers.SetLimit(runtime.NumCPU() / 2)
+
 	for accountHash, nodes := range diff.nodes.nodes {
-		subset := l.nodes[accountHash]
-		if subset == nil {
-			subset = make(map[string][]common.Hash)
-			l.nodes[accountHash] = subset
-		}
-		// Put the layer hash at the end of the list
-		for path := range nodes {
-			if _, exists := subset[path]; !exists {
-				subset[path] = getSlice()
+		workers.Go(func() error {
+			lock.Lock()
+			subset := l.nodes[accountHash]
+			if subset == nil {
+				subset = make(map[string][]common.Hash)
+				l.nodes[accountHash] = subset
 			}
-			subset[path] = append(subset[path], state)
-		}
+			lock.Unlock()
+
+			// Put the layer hash at the end of the list
+			for path := range nodes {
+				if _, exists := subset[path]; !exists {
+					subset[path] = getSlice()
+				}
+				subset[path] = append(subset[path], state)
+			}
+			return nil
+		})
 	}
+	workers.Wait()
 }
 
 // removeLayer traverses all the dirty nodes within the given diff layer and