Merge pull request #939 from iotaledger/fix/tiebreaker

Fix: Tiebreaker for chains with equal weight
iotaledger · Apr 26, 2024 · f405e3c · f405e3c
2 parents a8e457c + 0570f4d
commit f405e3c
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Showing 2 changed files with 30 additions and 17 deletions.
diff --git a/pkg/protocol/chain.go b/pkg/protocol/chain.go
@@ -20,6 +20,9 @@ type Chain struct {
 	// ParentChain contains the chain that this chain forked from.
 	ParentChain reactive.Variable[*Chain]
 
+	// DivergencePointVerified contains a flag that indicates whether the divergence point of this chain is verified.
+	DivergencePointVerified reactive.Event
+
 	// ChildChains contains the set of all chains that forked from this chain.
 	ChildChains reactive.Set[*Chain]
 
@@ -75,6 +78,7 @@ func newChain(chains *Chains) *Chain {
 	c := &Chain{
 		ForkingPoint:             reactive.NewVariable[*Commitment](),
 		ParentChain:              reactive.NewVariable[*Chain](),
+		DivergencePointVerified:  reactive.NewEvent(),
 		ChildChains:              reactive.NewSet[*Chain](),
 		LatestCommitment:         reactive.NewVariable[*Commitment](),
 		LatestAttestedCommitment: reactive.NewVariable[*Commitment](),
@@ -232,6 +236,8 @@ func (c *Chain) initDerivedProperties() (shutdown func()) {
 							c.deriveShouldEvict(forkingPoint, parentChain),
 						)
 					}),
+
+					c.deriveDivergencePointVerified(forkingPoint),
 				)
 			}),
 		),
@@ -290,6 +296,17 @@ func (c *Chain) deriveChildChains(child *Chain) (teardown func()) {
 	return
 }
 
+// deriveDivergencePointVerified defines how a chain determines whether its divergence point is verified.
+func (c *Chain) deriveDivergencePointVerified(forkingPoint *Commitment) (shutdown func()) {
+	return lo.Batch(
+		c.DivergencePointVerified.InheritFrom(forkingPoint.IsRoot),
+
+		forkingPoint.Parent.WithNonEmptyValue(func(parentOfForkingPoint *Commitment) (teardown func()) {
+			return c.DivergencePointVerified.InheritFrom(parentOfForkingPoint.IsVerified)
+		}),
+	)
+}
+
 // deriveParentChain defines how a chain determines its parent chain from its forking point (it inherits the Chain from
 // the parent commitment of the forking point or nil if either of them is still unknown).
 func (c *Chain) deriveParentChain(forkingPoint *Commitment) (shutdown func()) {

diff --git a/pkg/protocol/chains.go b/pkg/protocol/chains.go
@@ -323,13 +323,7 @@ func (c *Chains) initChainSwitching() (shutdown func()) {
 
 	return lo.BatchReverse(
 		c.HeaviestClaimedCandidate.WithNonEmptyValue(func(heaviestClaimedCandidate *Chain) (shutdown func()) {
-			return heaviestClaimedCandidate.ForkingPoint.WithNonEmptyValue(func(forkingPoint *Commitment) (teardown func()) {
-				return forkingPoint.Parent.WithNonEmptyValue(func(parentOfForkingPoint *Commitment) (teardown func()) {
-					return parentOfForkingPoint.IsVerified.WithNonEmptyValue(func(_ bool) (teardown func()) {
-						return heaviestClaimedCandidate.RequestAttestations.ToggleValue(true)
-					})
-				})
-			})
+			return heaviestClaimedCandidate.RequestAttestations.ToggleValue(true)
 		}),
 
 		c.HeaviestAttestedCandidate.OnUpdate(func(_ *Chain, heaviestAttestedCandidate *Chain) {
@@ -351,19 +345,21 @@ func (c *Chains) initChainSwitching() (shutdown func()) {
 
 func (c *Chains) trackHeaviestCandidates(chain *Chain) (teardown func()) {
 	return chain.LatestCommitment.OnUpdate(func(_ *Commitment, latestCommitment *Commitment) {
-		targetSlot := latestCommitment.ID().Index()
+		chain.DivergencePointVerified.OnTrigger(func() {
+			targetSlot := latestCommitment.ID().Index()
 
-		if evictionEvent := c.protocol.EvictionEvent(targetSlot); !evictionEvent.WasTriggered() {
-			c.HeaviestClaimedCandidate.registerCommitment(targetSlot, latestCommitment, evictionEvent)
+			if evictionEvent := c.protocol.EvictionEvent(targetSlot); !evictionEvent.WasTriggered() {
+				c.HeaviestClaimedCandidate.registerCommitment(targetSlot, latestCommitment, evictionEvent)
 
-			latestCommitment.IsAttested.OnTrigger(func() {
-				c.HeaviestAttestedCandidate.registerCommitment(targetSlot, latestCommitment, evictionEvent)
-			})
+				latestCommitment.IsAttested.OnTrigger(func() {
+					c.HeaviestAttestedCandidate.registerCommitment(targetSlot, latestCommitment, evictionEvent)
+				})
 
-			latestCommitment.IsVerified.OnTrigger(func() {
-				c.HeaviestVerifiedCandidate.registerCommitment(targetSlot, latestCommitment, evictionEvent)
-			})
-		}
+				latestCommitment.IsVerified.OnTrigger(func() {
+					c.HeaviestVerifiedCandidate.registerCommitment(targetSlot, latestCommitment, evictionEvent)
+				})
+			}
+		})
 	})
 }