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This commit is contained in:
Paul Hauner
2020-01-15 15:33:35 +11:00
parent 90b57829b3
commit 029fb24858
1 changed files with 28 additions and 0 deletions
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28
eth2/proto_array_fork_choice/src/proto_array.rs
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@@ -289,6 +289,18 @@ impl ProtoArray {
Ok(())
}
/// Observe the parent at `parent_index` with respect to the child at `child_index` and
/// potentially modify the `parent.best_child` and `parent.best_descendant` values.
///
/// ## Detail
///
/// There are four outcomes:
///
/// - The child is already the best child but it's now invalid due to a FFG change and should be removed.
/// - The child is already the best child and the parent is updated with the new
/// best-descendant.
/// - The child is not the best child but becomes the best child.
/// - The child is not the best child and does not become the best child.
fn maybe_update_best_child_and_descendant(
&mut self,
parent_index: usize,
@@ -306,6 +318,10 @@ impl ProtoArray {
let child_leads_to_viable_head = self.node_leads_to_viable_head(&child)?;
// These three variables are aliases to the three options that we may set the
// `parent.best_child` and `parent.best_descendant` to.
//
// I use the aliases to assist readability.
let change_to_none = (None, None);
let change_to_child = (
Some(child_index),
@@ -316,8 +332,12 @@ impl ProtoArray {
let (new_best_child, new_best_descendant) =
if let Some(best_child_index) = parent.best_child {
if best_child_index == child_index && !child_leads_to_viable_head {
// If the child is already the best-child of the parent but it's not viable for
// the head, remove it.
change_to_none
} else if best_child_index == child_index {
// If the child is the best-child already, set it again to ensure that the
// best-descendant of the parent is updated.
change_to_child
} else {
let best_child = self
@@ -330,16 +350,20 @@ impl ProtoArray {
self.node_leads_to_viable_head(&best_child)?;
if child_leads_to_viable_head && !best_child_leads_to_viable_head {
// The child leads to a viable head, but the current best-child doesn't.
change_to_child
} else if !child_leads_to_viable_head && best_child_leads_to_viable_head {
// The best child leads to a viable head, but the child doesn't.
no_change
} else if child.weight == best_child.weight {
// Tie-breaker of equal weights by root.
if child.root >= best_child.root {
change_to_child
} else {
no_change
}
} else {
// Choose the winner by weight.
if child.weight >= best_child.weight {
change_to_child
} else {
@@ -349,8 +373,10 @@ impl ProtoArray {
}
} else {
if child_leads_to_viable_head {
// There is no current best-child and the child is viable.
change_to_child
} else {
// There is no current-best child but the child is not viable.
no_change
}
};
@@ -365,6 +391,8 @@ impl ProtoArray {
Ok(())
}
/// Indicates if the node itself is viable for the head, or if it's best descendant is viable
/// for the head.
fn node_leads_to_viable_head(&self, node: &ProtoNode) -> Result<bool, Error> {
let best_descendant_is_viable_for_head =
if let Some(best_descendant_index) = node.best_descendant {