perlin4.go

// Searches for suitable parent transactions for a new transaction.
func (n *Node) SelectParents() []string {
  // [OT] The lock could be held for less time with BFS
  mutex.RLock()
  defer mutex.RUnlock()
  var eligibleParents []*Transaction
  // [OT] Search every historical transaction.
  for _, tx := range n.Transactions {
    if n.IsStronglyPreferred(tx) {
      // [OT] Figure 19, line 2
      if len(n.Conflicts[tx.Body.Utxo].Transactions) == 1 ||
n.Confidence(tx) > 0 {
        eligibleParents = append(eligibleParents, tx)
      }
    }
  }
  // [OT] Parents are strings rather than typed transactions.
  var parents []string
  // [OT] Figure 19, line 3
  // Parents are defined as tx's whose children are not eligible parents
  // themselves.
  for _, x := range eligibleParents {
    var children []*Transaction
    // [OT] This is O(n^2) in the number of transactions...
    //      Could be avoided by storing the graph in topological order, or
    //      including child pointers.
    // Get all children of the candidate parent.
    for _, tx := range n.Transactions {
      for _, parentId := range tx.Body.GetParents() {
        if parentId == x.Id {
          children = append(children, tx)
        }
      }
    }
    // [OT] Does golang not have a set()? 
    //      eligible := set(children).intersect(eligibleParents).length == 0
    eligible := true
    // Check if the child is an eligible parent himself.
    for _, y := range eligibleParents {
      for _, child := range children {
        if y.Id == child.Id {
          eligible = false
          break
        }
      }
    }
    if eligible {
      parents = append(parents, x.Id)
    }
  }
  // [OT] No sampling here or up the stack.
  return parents
}