use nil instead of empty digest

Author: samliok

epoch.go

@@ -1577,13 +1577,13 @@ func (e *Epoch) handleBlockMessage(message *BlockMessage, from NodeID) error {
 // It returns the digest of the previous block it depends on (or emptyDigest if none),
 // as well as a list of rounds for which it needs to verify empty notarizations.
 // TODO: we should request empty notarizations if we don't have them
-func (e *Epoch) blockDependencies(bh BlockHeader) (Digest, []uint64) {
+func (e *Epoch) blockDependencies(bh BlockHeader) (*Digest, []uint64) {
 	if bh.Seq == 0 {
 		// genesis block has no dependencies
-		return emptyDigest, nil
+		return nil, nil
 	}
 
-	prevBlockDependency := bh.Prev
+	prevBlockDependency := &bh.Prev
 
 	prevBlock, notarizationOrFinalization, found := e.locateBlock(bh.Seq-1, bh.Prev[:])
 	if !found {
@@ -1592,12 +1592,12 @@ func (e *Epoch) blockDependencies(bh BlockHeader) (Digest, []uint64) {
 			zap.Uint64("seq", bh.Seq-1),
 			zap.Stringer("prev", bh.Prev))
 
-		return emptyDigest, nil
+		return nil, nil
 	}
 
 	// no block dependency if we already have a notarization or finalization for the previous block
 	if notarizationOrFinalization != nil {
-		prevBlockDependency = emptyDigest
+		prevBlockDependency = nil
 	}
 
 	// missing empty rounds
@@ -1928,10 +1928,10 @@ func (e *Epoch) createNotarizedBlockVerificationTask(block Block, notarization N
 
 // finalizedBlockDependency returns the dependency digest for a block that has a finalization.
 // We do not care about empty notarizations since the block is finalized.
-func (e *Epoch) finalizedBlockDependency(md BlockHeader) Digest {
+func (e *Epoch) finalizedBlockDependency(md BlockHeader) *Digest {
 	if md.Seq == 0 {
 		// genesis block has no dependencies
-		return emptyDigest
+		return nil
 	}
 
 	// A block can be scheduled if its predecessor is either notarized or finalized.
@@ -1942,14 +1942,14 @@ func (e *Epoch) finalizedBlockDependency(md BlockHeader) Digest {
 			zap.Uint64("seq", md.Seq-1),
 			zap.Stringer("prev", md.Prev))
 
-		return emptyDigest
+		return nil
 	}
 
 	if notarizedOrFinalized != nil {
-		return emptyDigest
+		return nil
 	}
 
-	return md.Prev
+	return &md.Prev
 }
 
 // VerifyBlockMessageVote checks if we have the block in the future messages map.
@@ -2142,7 +2142,7 @@ func (e *Epoch) buildBlock() {
 	}
 
 	e.Logger.Debug("Scheduling block building", zap.Uint64("round", metadata.Round))
-	e.sched.Schedule(task, emptyDigest, []uint64{})
+	e.sched.Schedule(task, nil, []uint64{})
 }
 
 func (e *Epoch) retrieveBlacklistOfParentBlock(metadata ProtocolMetadata) (Blacklist, bool) {

sched.go

@@ -114,7 +114,7 @@ func (as *Scheduler) run() {
 	}
 }
 
-func (as *Scheduler) Schedule(f func() Digest, prevDependency Digest, emptyRounds []uint64) {
+func (as *Scheduler) Schedule(f func() Digest, prevDependency *Digest, emptyRounds []uint64) {
 	as.lock.Lock()
 	defer as.lock.Unlock()
 
@@ -133,7 +133,7 @@ func (as *Scheduler) Schedule(f func() Digest, prevDependency Digest, emptyRound
 		EmptyRoundsDependency: emptyRoundDependencies,
 	}
 
-	ready := prevDependency == emptyDigest && len(emptyRoundDependencies) == 0
+	ready := prevDependency == nil && len(emptyRoundDependencies) == 0
 	if !ready {
 		as.logger.Debug("Scheduling task", zap.Stringer("block dependency", prevDependency), zap.Uint64s("empty round dependencies", emptyRounds))
 		as.pending.Insert(task) // (9)
@@ -184,7 +184,7 @@ func (as *Scheduler) ExecuteEmptyNotarizationDependents(round uint64) {
 type Task struct {
 	F func() Digest
 
-	ParentBlockDependency Digest
+	ParentBlockDependency *Digest
 	EmptyRoundsDependency map[uint64]struct{}
 }
 
@@ -218,9 +218,13 @@ func (d *dependencies) RemoveDigest(id Digest) []Task {
 
 	for _, task := range d.tasks {
 		var removed bool
+		if task.ParentBlockDependency == nil {
+			continue
+		}
+
 		// Check if the task depends on the given digest
-		if task.ParentBlockDependency == id {
-			task.ParentBlockDependency = emptyDigest
+		if *task.ParentBlockDependency == id {
+			task.ParentBlockDependency = nil
 			// If the task has no other dependencies, it's ready to run
 			if len(task.EmptyRoundsDependency) == 0 {
 				ready = append(ready, task)
@@ -250,7 +254,7 @@ func (d *dependencies) RemoveEmptyNotarization(round uint64) []Task {
 		if _, exists := task.EmptyRoundsDependency[round]; exists {
 			delete(task.EmptyRoundsDependency, round)
 			// If the task has no other dependencies, it's ready to run
-			if task.ParentBlockDependency == emptyDigest && len(task.EmptyRoundsDependency) == 0 {
+			if task.ParentBlockDependency == nil && len(task.EmptyRoundsDependency) == 0 {
 				ready = append(ready, task)
 				removed = true
 			}