eth/catalyst: ensure period zero mode leaves no pending txs in pool

eth/catalyst/api.go

@@ -184,7 +184,7 @@ func (api *ConsensusAPI) ForkchoiceUpdatedV1(update engine.ForkchoiceStateV1, pa
 			return engine.STATUS_INVALID, engine.InvalidParams.With(errors.New("forkChoiceUpdateV1 called post-shanghai"))
 		}
 	}
-	return api.forkchoiceUpdated(update, payloadAttributes, engine.PayloadV1, false)
+	return api.forkchoiceUpdated(update, payloadAttributes, engine.PayloadV1)
 }
 
 // ForkchoiceUpdatedV2 is equivalent to V1 with the addition of withdrawals in the payload
@@ -207,7 +207,7 @@ func (api *ConsensusAPI) ForkchoiceUpdatedV2(update engine.ForkchoiceStateV1, pa
 			return engine.STATUS_INVALID, engine.UnsupportedFork.With(errors.New("forkchoiceUpdatedV2 must only be called with paris and shanghai payloads"))
 		}
 	}
-	return api.forkchoiceUpdated(update, params, engine.PayloadV2, false)
+	return api.forkchoiceUpdated(update, params, engine.PayloadV2)
 }
 
 // ForkchoiceUpdatedV3 is equivalent to V2 with the addition of parent beacon block root
@@ -228,10 +228,10 @@ func (api *ConsensusAPI) ForkchoiceUpdatedV3(update engine.ForkchoiceStateV1, pa
 	// hash, even if params are wrong. To do this we need to split up
 	// forkchoiceUpdate into a function that only updates the head and then a
 	// function that kicks off block construction.
-	return api.forkchoiceUpdated(update, params, engine.PayloadV3, false)
+	return api.forkchoiceUpdated(update, params, engine.PayloadV3)
 }
 
-func (api *ConsensusAPI) forkchoiceUpdated(update engine.ForkchoiceStateV1, payloadAttributes *engine.PayloadAttributes, payloadVersion engine.PayloadVersion, simulatorMode bool) (engine.ForkChoiceResponse, error) {
+func (api *ConsensusAPI) forkchoiceUpdated(update engine.ForkchoiceStateV1, payloadAttributes *engine.PayloadAttributes, payloadVersion engine.PayloadVersion) (engine.ForkChoiceResponse, error) {
 	api.forkchoiceLock.Lock()
 	defer api.forkchoiceLock.Unlock()
 
@@ -374,19 +374,6 @@ func (api *ConsensusAPI) forkchoiceUpdated(update engine.ForkchoiceStateV1, payl
 		if api.localBlocks.has(id) {
 			return valid(&id), nil
 		}
-		// If the beacon chain is ran by a simulator, then transaction insertion,
-		// block insertion and block production will happen without any timing
-		// delay between them. This will cause flaky simulator executions due to
-		// the transaction pool running its internal reset operation on a back-
-		// ground thread. To avoid the racey behavior - in simulator mode - the
-		// pool will be explicitly blocked on its reset before continuing to the
-		// block production below.
-		if simulatorMode {
-			if err := api.eth.TxPool().Sync(); err != nil {
-				log.Error("Failed to sync transaction pool", "err", err)
-				return valid(nil), engine.InvalidPayloadAttributes.With(err)
-			}
-		}
 		payload, err := api.eth.Miner().BuildPayload(args)
 		if err != nil {
 			log.Error("Failed to build payload", "err", err)

eth/catalyst/simulated_beacon.go

@@ -20,6 +20,7 @@ import (
 	"crypto/rand"
 	"crypto/sha256"
 	"errors"
+	"fmt"
 	"math/big"
 	"sync"
 	"time"
@@ -30,6 +31,7 @@ import (
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/crypto/kzg4844"
 	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/params"
@@ -41,36 +43,46 @@ const devEpochLength = 32
 // withdrawalQueue implements a FIFO queue which holds withdrawals that are
 // pending inclusion.
 type withdrawalQueue struct {
-	pending chan *types.Withdrawal
+	pending types.Withdrawals
+	mu      sync.Mutex
+	feed    event.Feed
+	subs    event.SubscriptionScope
 }
 
+type newWithdrawalsEvent struct{ Withdrawals types.Withdrawals }
+
 // add queues a withdrawal for future inclusion.
 func (w *withdrawalQueue) add(withdrawal *types.Withdrawal) error {
-	select {
-	case w.pending <- withdrawal:
-		break
-	default:
-		return errors.New("withdrawal queue full")
-	}
+	w.mu.Lock()
+	w.pending = append(w.pending, withdrawal)
+	w.mu.Unlock()
+
+	w.feed.Send(newWithdrawalsEvent{types.Withdrawals{withdrawal}})
 	return nil
 }
 
-// gatherPending returns a number of queued withdrawals up to a maximum count.
-func (w *withdrawalQueue) gatherPending(maxCount int) []*types.Withdrawal {
-	withdrawals := []*types.Withdrawal{}
-	for {
-		select {
-		case withdrawal := <-w.pending:
-			withdrawals = append(withdrawals, withdrawal)
-			if len(withdrawals) == maxCount {
-				return withdrawals
-			}
-		default:
-			return withdrawals
-		}
-	}
+// pop dequeues the specified number of withdrawals from the queue.
+func (w *withdrawalQueue) pop(count int) types.Withdrawals {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	count = min(count, len(w.pending))
+	popped := w.pending[0:count]
+	w.pending = w.pending[count:]
+
+	return popped
+}
+
+// subscribe allows a listener to be updated when new withdrawals are added to
+// the queue.
+func (w *withdrawalQueue) subscribe(ch chan<- newWithdrawalsEvent) event.Subscription {
+	sub := w.feed.Subscribe(ch)
+	return w.subs.Track(sub)
 }
 
+// SimulatedBeacon drives an Ethereum instance as if it were a real beacon
+// client. It can run in period mode where it mines a new block every period
+// (seconds) or on every transaction via Commit, Fork and AdjustTime.
 type SimulatedBeacon struct {
 	shutdownCh  chan struct{}
 	eth         *eth.Ethereum
@@ -86,10 +98,6 @@ type SimulatedBeacon struct {
 }
 
 // NewSimulatedBeacon constructs a new simulated beacon chain.
-// Period sets the period in which blocks should be produced.
-//
-//   - If period is set to 0, a block is produced on every transaction.
-//     via Commit, Fork and AdjustTime.
 func NewSimulatedBeacon(period uint64, eth *eth.Ethereum) (*SimulatedBeacon, error) {
 	block := eth.BlockChain().CurrentBlock()
 	current := engine.ForkchoiceStateV1{
@@ -112,7 +120,6 @@ func NewSimulatedBeacon(period uint64, eth *eth.Ethereum) (*SimulatedBeacon, err
 		engineAPI:          engineAPI,
 		lastBlockTime:      block.Time,
 		curForkchoiceState: current,
-		withdrawals:        withdrawalQueue{make(chan *types.Withdrawal, 20)},
 	}, nil
 }
 
@@ -156,6 +163,16 @@ func (c *SimulatedBeacon) sealBlock(withdrawals []*types.Withdrawal, timestamp u
 		c.setCurrentState(header.Hash(), *finalizedHash)
 	}
 
+	// Because transaction insertion, block insertion, and block production will
+	// happen without any timing delay between them in simulator mode and the
+	// transaction pool will be running its internal reset operation on a
+	// background thread, flaky executions can happen. To avoid the racey
+	// behavior, the pool will be explicitly blocked on its reset before
+	// continuing to the block production below.
+	if err := c.eth.APIBackend.TxPool().Sync(); err != nil {
+		return fmt.Errorf("failed to sync txpool: %w", err)
+	}
+
 	var random [32]byte
 	rand.Read(random[:])
 	fcResponse, err := c.engineAPI.forkchoiceUpdated(c.curForkchoiceState, &engine.PayloadAttributes{
@@ -164,13 +181,14 @@ func (c *SimulatedBeacon) sealBlock(withdrawals []*types.Withdrawal, timestamp u
 		Withdrawals:           withdrawals,
 		Random:                random,
 		BeaconRoot:            &common.Hash{},
-	}, engine.PayloadV3, true)
+	}, engine.PayloadV3)
 	if err != nil {
 		return err
 	}
 	if fcResponse == engine.STATUS_SYNCING {
 		return errors.New("chain rewind prevented invocation of payload creation")
 	}
+
 	envelope, err := c.engineAPI.getPayload(*fcResponse.PayloadID, true)
 	if err != nil {
 		return err
@@ -223,8 +241,7 @@ func (c *SimulatedBeacon) loop() {
 		case <-c.shutdownCh:
 			return
 		case <-timer.C:
-			withdrawals := c.withdrawals.gatherPending(10)
-			if err := c.sealBlock(withdrawals, uint64(time.Now().Unix())); err != nil {
+			if err := c.sealBlock(c.withdrawals.pop(10), uint64(time.Now().Unix())); err != nil {
 				log.Warn("Error performing sealing work", "err", err)
 			} else {
 				timer.Reset(time.Second * time.Duration(c.period))
@@ -260,7 +277,7 @@ func (c *SimulatedBeacon) setCurrentState(headHash, finalizedHash common.Hash) {
 
 // Commit seals a block on demand.
 func (c *SimulatedBeacon) Commit() common.Hash {
-	withdrawals := c.withdrawals.gatherPending(10)
+	withdrawals := c.withdrawals.pop(10)
 	if err := c.sealBlock(withdrawals, uint64(time.Now().Unix())); err != nil {
 		log.Warn("Error performing sealing work", "err", err)
 	}
@@ -301,16 +318,14 @@ func (c *SimulatedBeacon) AdjustTime(adjustment time.Duration) error {
 	if parent == nil {
 		return errors.New("parent not found")
 	}
-	withdrawals := c.withdrawals.gatherPending(10)
+	withdrawals := c.withdrawals.pop(10)
 	return c.sealBlock(withdrawals, parent.Time+uint64(adjustment/time.Second))
 }
 
+// RegisterSimulatedBeaconAPIs registers the simulated beacon's API with the
+// stack.
 func RegisterSimulatedBeaconAPIs(stack *node.Node, sim *SimulatedBeacon) {
-	api := &api{sim}
-	if sim.period == 0 {
-		// mine on demand if period is set to 0
-		go api.loop()
-	}
+	api := newSimulatedBeaconAPI(sim)
 	stack.RegisterAPIs([]rpc.API{
 		{
 			Namespace: "dev",

eth/catalyst/simulated_beacon_api.go

@@ -18,44 +18,88 @@ package catalyst
 
 import (
 	"context"
-	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
-	"github.com/ethereum/go-ethereum/log"
 )
 
-type api struct {
+// simulatedBeaconAPI provides a RPC API for SimulatedBeacon.
+type simulatedBeaconAPI struct {
 	sim *SimulatedBeacon
 }
 
-func (a *api) loop() {
+// newSimulatedBeaconAPI returns an instance of simulatedBeaconAPI with a
+// buffered commit channel. If period is zero, it starts a goroutine to handle
+// new tx events.
+func newSimulatedBeaconAPI(sim *SimulatedBeacon) *simulatedBeaconAPI {
+	api := &simulatedBeaconAPI{sim: sim}
+	if sim.period == 0 {
+		// mine on demand if period is set to 0
+		go api.loop()
+	}
+	return api
+}
+
+// loop is the main loop for the API when it's running in period = 0 mode. It
+// ensures that block production is triggered as soon as a new withdrawal or
+// transaction is received.
+func (a *simulatedBeaconAPI) loop() {
 	var (
-		newTxs = make(chan core.NewTxsEvent)
-		sub    = a.sim.eth.TxPool().SubscribeTransactions(newTxs, true)
+		newTxs    = make(chan core.NewTxsEvent)
+		newWxs    = make(chan newWithdrawalsEvent)
+		newTxsSub = a.sim.eth.TxPool().SubscribeTransactions(newTxs, true)
+		newWxsSub = a.sim.withdrawals.subscribe(newWxs)
+		doCommit  = make(chan struct{}, 1)
 	)
-	defer sub.Unsubscribe()
+	defer newTxsSub.Unsubscribe()
+	defer newWxsSub.Unsubscribe()
+
+	// A background thread which signals to the simulator when to commit
+	// based on messages over doCommit.
+	go func() {
+		for range doCommit {
+			a.sim.Commit()
+			a.sim.eth.TxPool().Sync()
+
+			// It's worth noting that in case a tx ends up in the pool listed as
+			// "executable", but for whatever reason the miner does not include it in
+			// a block -- maybe the miner is enforcing a higher tip than the pool --
+			// this code will spinloop.
+			for {
+				if executable, _ := a.sim.eth.TxPool().Stats(); executable == 0 {
+					break
+				}
+				a.sim.Commit()
+			}
+		}
+	}()
 
 	for {
 		select {
 		case <-a.sim.shutdownCh:
+			close(doCommit)
 			return
-		case w := <-a.sim.withdrawals.pending:
-			withdrawals := append(a.sim.withdrawals.gatherPending(9), w)
-			if err := a.sim.sealBlock(withdrawals, uint64(time.Now().Unix())); err != nil {
-				log.Warn("Error performing sealing work", "err", err)
+		case <-newWxs:
+			select {
+			case doCommit <- struct{}{}:
+			default:
 			}
 		case <-newTxs:
-			a.sim.Commit()
+			select {
+			case doCommit <- struct{}{}:
+			default:
+			}
 		}
 	}
 }
 
-func (a *api) AddWithdrawal(ctx context.Context, withdrawal *types.Withdrawal) error {
+// AddWithdrawal adds a withdrawal to the pending queue.
+func (a *simulatedBeaconAPI) AddWithdrawal(ctx context.Context, withdrawal *types.Withdrawal) error {
 	return a.sim.withdrawals.add(withdrawal)
 }
 
-func (a *api) SetFeeRecipient(ctx context.Context, feeRecipient common.Address) {
+// SetFeeRecipient sets the fee recipient for block building purposes.
+func (a *simulatedBeaconAPI) SetFeeRecipient(ctx context.Context, feeRecipient common.Address) {
 	a.sim.setFeeRecipient(feeRecipient)
 }