Merge pull request #1898 from karalabe/eventmux-post-race

core, eth, event, miner, xeth: fix event post / subscription race

core/blockchain.go

@@ -483,13 +483,6 @@ func (bc *BlockChain) Stop() {
 	glog.V(logger.Info).Infoln("Chain manager stopped")
 }
 
-type queueEvent struct {
-	queue          []interface{}
-	canonicalCount int
-	sideCount      int
-	splitCount     int
-}
-
 func (self *BlockChain) procFutureBlocks() {
 	blocks := make([]*types.Block, self.futureBlocks.Len())
 	for i, hash := range self.futureBlocks.Keys() {
@@ -573,10 +566,9 @@ func (self *BlockChain) InsertChain(chain types.Blocks) (int, error) {
 	// faster than direct delivery and requires much less mutex
 	// acquiring.
 	var (
-		queue      = make([]interface{}, len(chain))
-		queueEvent = queueEvent{queue: queue}
-		stats      struct{ queued, processed, ignored int }
-		tstart     = time.Now()
+		stats  struct{ queued, processed, ignored int }
+		events = make([]interface{}, 0, len(chain))
+		tstart = time.Now()
 
 		nonceChecked = make([]bool, len(chain))
 	)
@@ -659,22 +651,21 @@ func (self *BlockChain) InsertChain(chain types.Blocks) (int, error) {
 			if glog.V(logger.Debug) {
 				glog.Infof("[%v] inserted block #%d (%d TXs %v G %d UNCs) (%x...). Took %v\n", time.Now().UnixNano(), block.Number(), len(block.Transactions()), block.GasUsed(), len(block.Uncles()), block.Hash().Bytes()[0:4], time.Since(bstart))
 			}
-			queue[i] = ChainEvent{block, block.Hash(), logs}
-			queueEvent.canonicalCount++
+			events = append(events, ChainEvent{block, block.Hash(), logs})
 
 			// This puts transactions in a extra db for rpc
 			PutTransactions(self.chainDb, block, block.Transactions())
 			// store the receipts
 			PutReceipts(self.chainDb, receipts)
+
 		case SideStatTy:
 			if glog.V(logger.Detail) {
 				glog.Infof("inserted forked block #%d (TD=%v) (%d TXs %d UNCs) (%x...). Took %v\n", block.Number(), block.Difficulty(), len(block.Transactions()), len(block.Uncles()), block.Hash().Bytes()[0:4], time.Since(bstart))
 			}
-			queue[i] = ChainSideEvent{block, logs}
-			queueEvent.sideCount++
+			events = append(events, ChainSideEvent{block, logs})
+
 		case SplitStatTy:
-			queue[i] = ChainSplitEvent{block, logs}
-			queueEvent.splitCount++
+			events = append(events, ChainSplitEvent{block, logs})
 		}
 		stats.processed++
 	}
@@ -684,8 +675,7 @@ func (self *BlockChain) InsertChain(chain types.Blocks) (int, error) {
 		start, end := chain[0], chain[len(chain)-1]
 		glog.Infof("imported %d block(s) (%d queued %d ignored) including %d txs in %v. #%v [%x / %x]\n", stats.processed, stats.queued, stats.ignored, txcount, tend, end.Number(), start.Hash().Bytes()[:4], end.Hash().Bytes()[:4])
 	}
-
-	go self.eventMux.Post(queueEvent)
+	go self.postChainEvents(events)
 
 	return 0, nil
 }
@@ -774,32 +764,31 @@ func (self *BlockChain) reorg(oldBlock, newBlock *types.Block) error {
 	return nil
 }
 
+// postChainEvents iterates over the events generated by a chain insertion and
+// posts them into the event mux.
+func (self *BlockChain) postChainEvents(events []interface{}) {
+	for _, event := range events {
+		if event, ok := event.(ChainEvent); ok {
+			// We need some control over the mining operation. Acquiring locks and waiting for the miner to create new block takes too long
+			// and in most cases isn't even necessary.
+			if self.currentBlock.Hash() == event.Hash {
+				self.currentGasLimit = CalcGasLimit(event.Block)
+				self.eventMux.Post(ChainHeadEvent{event.Block})
+			}
+		}
+		// Fire the insertion events individually too
+		self.eventMux.Post(event)
+	}
+}
+
 func (self *BlockChain) update() {
-	events := self.eventMux.Subscribe(queueEvent{})
 	futureTimer := time.Tick(5 * time.Second)
-out:
 	for {
 		select {
-		case ev := <-events.Chan():
-			switch ev := ev.(type) {
-			case queueEvent:
-				for _, event := range ev.queue {
-					switch event := event.(type) {
-					case ChainEvent:
-						// We need some control over the mining operation. Acquiring locks and waiting for the miner to create new block takes too long
-						// and in most cases isn't even necessary.
-						if self.currentBlock.Hash() == event.Hash {
-							self.currentGasLimit = CalcGasLimit(event.Block)
-							self.eventMux.Post(ChainHeadEvent{event.Block})
-						}
-					}
-					self.eventMux.Post(event)
-				}
-			}
 		case <-futureTimer:
 			self.procFutureBlocks()
 		case <-self.quit:
-			break out
+			return
 		}
 	}
 }

core/transaction_pool.go

@@ -93,7 +93,7 @@ func (pool *TxPool) eventLoop() {
 	// we need to know the new state. The new state will help us determine
 	// the nonces in the managed state
 	for ev := range pool.events.Chan() {
-		switch ev := ev.(type) {
+		switch ev := ev.Data.(type) {
 		case ChainHeadEvent:
 			pool.mu.Lock()
 			pool.resetState()

eth/filters/filter_system.go

@@ -20,6 +20,7 @@ package filters
 
 import (
 	"sync"
+	"time"
 
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/vm"
@@ -35,6 +36,7 @@ type FilterSystem struct {
 	filterMu sync.RWMutex
 	filterId int
 	filters  map[int]*Filter
+	created  map[int]time.Time
 
 	quit chan struct{}
 }
@@ -44,6 +46,7 @@ func NewFilterSystem(mux *event.TypeMux) *FilterSystem {
 	fs := &FilterSystem{
 		eventMux: mux,
 		filters:  make(map[int]*Filter),
+		created:  make(map[int]time.Time),
 	}
 	go fs.filterLoop()
 	return fs
@@ -60,6 +63,7 @@ func (fs *FilterSystem) Add(filter *Filter) (id int) {
 	defer fs.filterMu.Unlock()
 	id = fs.filterId
 	fs.filters[id] = filter
+	fs.created[id] = time.Now()
 	fs.filterId++
 
 	return id
@@ -69,15 +73,16 @@ func (fs *FilterSystem) Add(filter *Filter) (id int) {
 func (fs *FilterSystem) Remove(id int) {
 	fs.filterMu.Lock()
 	defer fs.filterMu.Unlock()
-	if _, ok := fs.filters[id]; ok {
-		delete(fs.filters, id)
-	}
+
+	delete(fs.filters, id)
+	delete(fs.created, id)
 }
 
 // Get retrieves a filter installed using Add The filter may not be modified.
 func (fs *FilterSystem) Get(id int) *Filter {
 	fs.filterMu.RLock()
 	defer fs.filterMu.RUnlock()
+
 	return fs.filters[id]
 }
 
@@ -85,42 +90,49 @@ func (fs *FilterSystem) Get(id int) *Filter {
 // when the filter matches the requirements.
 func (fs *FilterSystem) filterLoop() {
 	// Subscribe to events
-	events := fs.eventMux.Subscribe(
+	eventCh := fs.eventMux.Subscribe(
 		//core.PendingBlockEvent{},
 		core.ChainEvent{},
 		core.TxPreEvent{},
-		vm.Logs(nil))
+		vm.Logs(nil),
+	).Chan()
 
 out:
 	for {
 		select {
 		case <-fs.quit:
 			break out
-		case event := <-events.Chan():
-			switch event := event.(type) {
+		case event, ok := <-eventCh:
+			if !ok {
+				// Event subscription closed, set the channel to nil to stop spinning
+				eventCh = nil
+				continue
+			}
+			// A real event arrived, notify the registered filters
+			switch ev := event.Data.(type) {
 			case core.ChainEvent:
 				fs.filterMu.RLock()
-				for _, filter := range fs.filters {
-					if filter.BlockCallback != nil {
-						filter.BlockCallback(event.Block, event.Logs)
+				for id, filter := range fs.filters {
+					if filter.BlockCallback != nil && fs.created[id].Before(event.Time) {
+						filter.BlockCallback(ev.Block, ev.Logs)
 					}
 				}
 				fs.filterMu.RUnlock()
 
 			case core.TxPreEvent:
 				fs.filterMu.RLock()
-				for _, filter := range fs.filters {
-					if filter.TransactionCallback != nil {
-						filter.TransactionCallback(event.Tx)
+				for id, filter := range fs.filters {
+					if filter.TransactionCallback != nil && fs.created[id].Before(event.Time) {
+						filter.TransactionCallback(ev.Tx)
 					}
 				}
 				fs.filterMu.RUnlock()
 
 			case vm.Logs:
 				fs.filterMu.RLock()
-				for _, filter := range fs.filters {
-					if filter.LogsCallback != nil {
-						msgs := filter.FilterLogs(event)
+				for id, filter := range fs.filters {
+					if filter.LogsCallback != nil && fs.created[id].Before(event.Time) {
+						msgs := filter.FilterLogs(ev)
 						if len(msgs) > 0 {
 							filter.LogsCallback(msgs)
 						}

eth/gasprice.go

@@ -84,19 +84,16 @@ func (self *GasPriceOracle) processPastBlocks() {
 }
 
 func (self *GasPriceOracle) listenLoop() {
-	for {
-		ev, isopen := <-self.events.Chan()
-		if !isopen {
-			break
-		}
-		switch ev := ev.(type) {
+	defer self.events.Unsubscribe()
+
+	for event := range self.events.Chan() {
+		switch event := event.Data.(type) {
 		case core.ChainEvent:
-			self.processBlock(ev.Block)
+			self.processBlock(event.Block)
 		case core.ChainSplitEvent:
-			self.processBlock(ev.Block)
+			self.processBlock(event.Block)
 		}
 	}
-	self.events.Unsubscribe()
 }
 
 func (self *GasPriceOracle) processBlock(block *types.Block) {

eth/handler.go

@@ -687,7 +687,7 @@ func (pm *ProtocolManager) BroadcastTx(hash common.Hash, tx *types.Transaction)
 func (self *ProtocolManager) minedBroadcastLoop() {
 	// automatically stops if unsubscribe
 	for obj := range self.minedBlockSub.Chan() {
-		switch ev := obj.(type) {
+		switch ev := obj.Data.(type) {
 		case core.NewMinedBlockEvent:
 			self.BroadcastBlock(ev.Block, true)  // First propagate block to peers
 			self.BroadcastBlock(ev.Block, false) // Only then announce to the rest
@@ -698,7 +698,7 @@ func (self *ProtocolManager) minedBroadcastLoop() {
 func (self *ProtocolManager) txBroadcastLoop() {
 	// automatically stops if unsubscribe
 	for obj := range self.txSub.Chan() {
-		event := obj.(core.TxPreEvent)
+		event := obj.Data.(core.TxPreEvent)
 		self.BroadcastTx(event.Tx.Hash(), event.Tx)
 	}
 }

event/event.go

@@ -22,14 +22,21 @@ import (
 	"fmt"
 	"reflect"
 	"sync"
+	"time"
 )
 
+// Event is a time-tagged notification pushed to subscribers.
+type Event struct {
+	Time time.Time
+	Data interface{}
+}
+
 // Subscription is implemented by event subscriptions.
 type Subscription interface {
 	// Chan returns a channel that carries events.
 	// Implementations should return the same channel
 	// for any subsequent calls to Chan.
-	Chan() <-chan interface{}
+	Chan() <-chan *Event
 
 	// Unsubscribe stops delivery of events to a subscription.
 	// The event channel is closed.
@@ -82,6 +89,10 @@ func (mux *TypeMux) Subscribe(types ...interface{}) Subscription {
 // Post sends an event to all receivers registered for the given type.
 // It returns ErrMuxClosed if the mux has been stopped.
 func (mux *TypeMux) Post(ev interface{}) error {
+	event := &Event{
+		Time: time.Now(),
+		Data: ev,
+	}
 	rtyp := reflect.TypeOf(ev)
 	mux.mutex.RLock()
 	if mux.stopped {
@@ -91,7 +102,7 @@ func (mux *TypeMux) Post(ev interface{}) error {
 	subs := mux.subm[rtyp]
 	mux.mutex.RUnlock()
 	for _, sub := range subs {
-		sub.deliver(ev)
+		sub.deliver(event)
 	}
 	return nil
 }
@@ -143,6 +154,7 @@ func posdelete(slice []*muxsub, pos int) []*muxsub {
 
 type muxsub struct {
 	mux     *TypeMux
+	created time.Time
 	closeMu sync.Mutex
 	closing chan struct{}
 	closed  bool
@@ -151,21 +163,22 @@ type muxsub struct {
 	// postC can be set to nil without affecting the return value of
 	// Chan.
 	postMu sync.RWMutex
-	readC  <-chan interface{}
-	postC  chan<- interface{}
+	readC  <-chan *Event
+	postC  chan<- *Event
 }
 
 func newsub(mux *TypeMux) *muxsub {
-	c := make(chan interface{})
+	c := make(chan *Event)
 	return &muxsub{
 		mux:     mux,
+		created: time.Now(),
 		readC:   c,
 		postC:   c,
 		closing: make(chan struct{}),
 	}
 }
 
-func (s *muxsub) Chan() <-chan interface{} {
+func (s *muxsub) Chan() <-chan *Event {
 	return s.readC
 }
 
@@ -189,11 +202,17 @@ func (s *muxsub) closewait() {
 	s.postMu.Unlock()
 }
 
-func (s *muxsub) deliver(ev interface{}) {
+func (s *muxsub) deliver(event *Event) {
+	// Short circuit delivery if stale event
+	if s.created.After(event.Time) {
+		return
+	}
+	// Otherwise deliver the event
 	s.postMu.RLock()
+	defer s.postMu.RUnlock()
+
 	select {
-	case s.postC <- ev:
+	case s.postC <- event:
 	case <-s.closing:
 	}
-	s.postMu.RUnlock()
 }

event/event_test.go

@@ -37,7 +37,7 @@ func TestSub(t *testing.T) {
 	}()
 	ev := <-sub.Chan()
 
-	if ev.(testEvent) != testEvent(5) {
+	if ev.Data.(testEvent) != testEvent(5) {
 		t.Errorf("Got %v (%T), expected event %v (%T)",
 			ev, ev, testEvent(5), testEvent(5))
 	}

event/example_test.go

@@ -30,7 +30,7 @@ func ExampleTypeMux() {
 	sub := mux.Subscribe(someEvent{}, otherEvent{})
 	go func() {
 		for event := range sub.Chan() {
-			fmt.Printf("Received: %#v\n", event)
+			fmt.Printf("Received: %#v\n", event.Data)
 		}
 		fmt.Println("done")
 		close(done)

miner/miner.go

@@ -66,7 +66,7 @@ func (self *Miner) update() {
 	events := self.mux.Subscribe(downloader.StartEvent{}, downloader.DoneEvent{}, downloader.FailedEvent{})
 out:
 	for ev := range events.Chan() {
-		switch ev.(type) {
+		switch ev.Data.(type) {
 		case downloader.StartEvent:
 			atomic.StoreInt32(&self.canStart, 0)
 			if self.Mining() {

miner/worker.go

@@ -215,13 +215,20 @@ func (self *worker) register(agent Agent) {
 }
 
 func (self *worker) update() {
-	events := self.mux.Subscribe(core.ChainHeadEvent{}, core.ChainSideEvent{}, core.TxPreEvent{})
+	eventSub := self.mux.Subscribe(core.ChainHeadEvent{}, core.ChainSideEvent{}, core.TxPreEvent{})
+	defer eventSub.Unsubscribe()
 
-out:
+	eventCh := eventSub.Chan()
 	for {
 		select {
-		case event := <-events.Chan():
-			switch ev := event.(type) {
+		case event, ok := <-eventCh:
+			if !ok {
+				// Event subscription closed, set the channel to nil to stop spinning
+				eventCh = nil
+				continue
+			}
+			// A real event arrived, process interesting content
+			switch ev := event.Data.(type) {
 			case core.ChainHeadEvent:
 				self.commitNewWork()
 			case core.ChainSideEvent:
@@ -237,11 +244,9 @@ out:
 				}
 			}
 		case <-self.quit:
-			break out
+			return
 		}
 	}
-
-	events.Unsubscribe()
 }
 
 func newLocalMinedBlock(blockNumber uint64, prevMinedBlocks *uint64RingBuffer) (minedBlocks *uint64RingBuffer) {

xeth/xeth.go

@@ -244,30 +244,37 @@ func (self *XEth) State() *State { return self.state }
 func (self *XEth) UpdateState() (wait chan *big.Int) {
 	wait = make(chan *big.Int)
 	go func() {
-		sub := self.backend.EventMux().Subscribe(core.ChainHeadEvent{})
+		eventSub := self.backend.EventMux().Subscribe(core.ChainHeadEvent{})
+		defer eventSub.Unsubscribe()
+
 		var m, n *big.Int
 		var ok bool
-	out:
+
+		eventCh := eventSub.Chan()
 		for {
 			select {
-			case event := <-sub.Chan():
-				ev, ok := event.(core.ChainHeadEvent)
-				if ok {
-					m = ev.Block.Number()
+			case event, ok := <-eventCh:
+				if !ok {
+					// Event subscription closed, set the channel to nil to stop spinning
+					eventCh = nil
+					continue
+				}
+				// A real event arrived, process if new head block assignment
+				if event, ok := event.Data.(core.ChainHeadEvent); ok {
+					m = event.Block.Number()
 					if n != nil && n.Cmp(m) < 0 {
 						wait <- n
 						n = nil
 					}
-					statedb := state.New(ev.Block.Root(), self.backend.ChainDb())
+					statedb := state.New(event.Block.Root(), self.backend.ChainDb())
 					self.state = NewState(self, statedb)
 				}
 			case n, ok = <-wait:
 				if !ok {
-					break out
+					return
 				}
 			}
 		}
-		sub.Unsubscribe()
 	}()
 	return
 }