117 lines
2.9 KiB
Go
117 lines
2.9 KiB
Go
// Copyright (c) 2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package wtxmgr
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import (
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"github.com/btcsuite/btcd/chaincfg/chainhash"
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"github.com/btcsuite/btcd/wire"
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)
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type graphNode struct {
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value *wire.MsgTx
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outEdges []*chainhash.Hash
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inDegree int
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}
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type hashGraph map[chainhash.Hash]graphNode
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func makeGraph(set map[chainhash.Hash]*wire.MsgTx) hashGraph {
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graph := make(hashGraph)
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for _, tx := range set {
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// Add a node for every transaction. The output edges and input
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// degree are set by iterating over each transaction's inputs
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// below.
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txHash := tx.TxHash()
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if _, ok := graph[txHash]; !ok {
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graph[txHash] = graphNode{value: tx}
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}
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inputLoop:
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for _, input := range tx.TxIn {
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// Transaction inputs that reference transactions not
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// included in the set do not create any (local) graph
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// edges.
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if _, ok := set[input.PreviousOutPoint.Hash]; !ok {
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continue
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}
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inputNode := graph[input.PreviousOutPoint.Hash]
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// Skip duplicate edges.
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for _, outEdge := range inputNode.outEdges {
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if *outEdge == input.PreviousOutPoint.Hash {
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continue inputLoop
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}
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}
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// Mark a directed edge from the previous transaction
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// hash to this transaction and increase the input
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// degree for this transaction's node.
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inputTx := inputNode.value
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if inputTx == nil {
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inputTx = set[input.PreviousOutPoint.Hash]
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}
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graph[input.PreviousOutPoint.Hash] = graphNode{
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value: inputTx,
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outEdges: append(inputNode.outEdges, &txHash),
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inDegree: inputNode.inDegree,
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}
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node := graph[txHash]
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graph[txHash] = graphNode{
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value: tx,
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outEdges: node.outEdges,
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inDegree: node.inDegree + 1,
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}
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}
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}
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return graph
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}
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// graphRoots returns the roots of the graph. That is, it returns the node's
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// values for all nodes which contain an input degree of 0.
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func graphRoots(graph hashGraph) []*wire.MsgTx {
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roots := make([]*wire.MsgTx, 0, len(graph))
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for _, node := range graph {
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if node.inDegree == 0 {
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roots = append(roots, node.value)
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}
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}
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return roots
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}
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// DependencySort topologically sorts a set of transactions by their dependency
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// order. It is implemented using Kahn's algorithm.
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func DependencySort(txs map[chainhash.Hash]*wire.MsgTx) []*wire.MsgTx {
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graph := makeGraph(txs)
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s := graphRoots(graph)
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// If there are no edges (no transactions from the map reference each
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// other), then Kahn's algorithm is unnecessary.
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if len(s) == len(txs) {
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return s
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}
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sorted := make([]*wire.MsgTx, 0, len(txs))
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for len(s) != 0 {
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tx := s[0]
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s = s[1:]
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sorted = append(sorted, tx)
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n := graph[tx.TxHash()]
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for _, mHash := range n.outEdges {
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m := graph[*mHash]
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if m.inDegree != 0 {
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m.inDegree--
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graph[*mHash] = m
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if m.inDegree == 0 {
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s = append(s, m.value)
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}
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}
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}
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}
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return sorted
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}
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