miner: support disabling empty blockprecommits form the Go API (#20736)

* cmd, miner: add noempty-precommit flag

* cmd, miner: get rid of external flag

* miner: change bool to atomic int

* miner: fix tiny typo

Co-authored-by: Péter Szilágyi <peterke@gmail.com>

miner/miner.go

@@ -183,6 +183,23 @@ func (miner *Miner) SetEtherbase(addr common.Address) {
 	miner.worker.setEtherbase(addr)
 }
 
+// EnablePreseal turns on the preseal mining feature. It's enabled by default.
+// Note this function shouldn't be exposed to API, it's unnecessary for users
+// (miners) to actually know the underlying detail. It's only for outside project
+// which uses this library.
+func (miner *Miner) EnablePreseal() {
+	miner.worker.enablePreseal()
+}
+
+// DisablePreseal turns off the preseal mining feature. It's necessary for some
+// fake consensus engine which can seal blocks instantaneously.
+// Note this function shouldn't be exposed to API, it's unnecessary for users
+// (miners) to actually know the underlying detail. It's only for outside project
+// which uses this library.
+func (miner *Miner) DisablePreseal() {
+	miner.worker.disablePreseal()
+}
+
 // SubscribePendingLogs starts delivering logs from pending transactions
 // to the given channel.
 func (self *Miner) SubscribePendingLogs(ch chan<- []*types.Log) event.Subscription {

miner/worker.go

@@ -169,6 +169,13 @@ type worker struct {
 	running int32 // The indicator whether the consensus engine is running or not.
 	newTxs  int32 // New arrival transaction count since last sealing work submitting.
 
+	// noempty is the flag used to control whether the feature of pre-seal empty
+	// block is enabled. The default value is false(pre-seal is enabled by default).
+	// But in some special scenario the consensus engine will seal blocks instantaneously,
+	// in this case this feature will add all empty blocks into canonical chain
+	// non-stop and no real transaction will be included.
+	noempty uint32
+
 	// External functions
 	isLocalBlock func(block *types.Block) bool // Function used to determine whether the specified block is mined by local miner.
 
@@ -247,6 +254,16 @@ func (w *worker) setRecommitInterval(interval time.Duration) {
 	w.resubmitIntervalCh <- interval
 }
 
+// disablePreseal disables pre-sealing mining feature
+func (w *worker) disablePreseal() {
+	atomic.StoreUint32(&w.noempty, 1)
+}
+
+// enablePreseal enables pre-sealing mining feature
+func (w *worker) enablePreseal() {
+	atomic.StoreUint32(&w.noempty, 0)
+}
+
 // pending returns the pending state and corresponding block.
 func (w *worker) pending() (*types.Block, *state.StateDB) {
 	// return a snapshot to avoid contention on currentMu mutex
@@ -480,8 +497,9 @@ func (w *worker) mainLoop() {
 					w.updateSnapshot()
 				}
 			} else {
-				// If clique is running in dev mode(period is 0), disable
-				// advance sealing here.
+				// Special case, if the consensus engine is 0 period clique(dev mode),
+				// submit mining work here since all empty submission will be rejected
+				// by clique. Of course the advance sealing(empty submission) is disabled.
 				if w.chainConfig.Clique != nil && w.chainConfig.Clique.Period == 0 {
 					w.commitNewWork(nil, true, time.Now().Unix())
 				}
@@ -910,9 +928,9 @@ func (w *worker) commitNewWork(interrupt *int32, noempty bool, timestamp int64)
 	commitUncles(w.localUncles)
 	commitUncles(w.remoteUncles)
 
-	if !noempty {
-		// Create an empty block based on temporary copied state for sealing in advance without waiting block
-		// execution finished.
+	// Create an empty block based on temporary copied state for
+	// sealing in advance without waiting block execution finished.
+	if !noempty && atomic.LoadUint32(&w.noempty) == 0 {
 		w.commit(uncles, nil, false, tstart)
 	}
 
@@ -922,8 +940,10 @@ func (w *worker) commitNewWork(interrupt *int32, noempty bool, timestamp int64)
 		log.Error("Failed to fetch pending transactions", "err", err)
 		return
 	}
-	// Short circuit if there is no available pending transactions
-	if len(pending) == 0 {
+	// Short circuit if there is no available pending transactions.
+	// But if we disable empty precommit already, ignore it. Since
+	// empty block is necessary to keep the liveness of the network.
+	if len(pending) == 0 && atomic.LoadUint32(&w.noempty) == 0 {
 		w.updateSnapshot()
 		return
 	}