trie: utilize callbacks instead of amassing lists of hashes in database ref/unref

trie/database.go

@@ -214,6 +214,36 @@ func gatherChildren(n node, children *[]common.Hash) {
 	}
 }
 
+// forChilds invokes the callback for  all the tracked children of this node,
+// both the implicit ones  from inside the node as well as the explicit ones
+//from outside the node.
+func (n *cachedNode) forChilds(onChild func(hash common.Hash)) {
+	for child := range n.children {
+		onChild(child)
+	}
+	if _, ok := n.node.(rawNode); !ok {
+		forGatherChildren(n.node, onChild)
+	}
+}
+
+// forGatherChildren traverses the node hierarchy of a collapsed storage node and
+// invokes the callback for all the hashnode children.
+func forGatherChildren(n node, onChild func(hash common.Hash)) {
+	switch n := n.(type) {
+	case *rawShortNode:
+		forGatherChildren(n.Val, onChild)
+	case rawFullNode:
+		for i := 0; i < 16; i++ {
+			forGatherChildren(n[i], onChild)
+		}
+	case hashNode:
+		onChild(common.BytesToHash(n))
+	case valueNode, nil:
+	default:
+		panic(fmt.Sprintf("unknown node type: %T", n))
+	}
+}
+
 // simplifyNode traverses the hierarchy of an expanded memory node and discards
 // all the internal caches, returning a node that only contains the raw data.
 func simplifyNode(n node) node {
@@ -334,11 +364,11 @@ func (db *Database) insert(hash common.Hash, size int, node node) {
 		size:      uint16(size),
 		flushPrev: db.newest,
 	}
-	for _, child := range entry.childs() {
+	entry.forChilds(func(child common.Hash) {
 		if c := db.dirties[child]; c != nil {
 			c.parents++
 		}
-	}
+	})
 	db.dirties[hash] = entry
 
 	// Update the flush-list endpoints
@@ -570,9 +600,9 @@ func (db *Database) dereference(child common.Hash, parent common.Hash) {
 			db.dirties[node.flushNext].flushPrev = node.flushPrev
 		}
 		// Dereference all children and delete the node
-		for _, hash := range node.childs() {
+		node.forChilds(func(hash common.Hash) {
 			db.dereference(hash, child)
-		}
+		})
 		delete(db.dirties, child)
 		db.dirtiesSize -= common.StorageSize(common.HashLength + int(node.size))
 		if node.children != nil {