miner: move agent logic to worker (#17351)

* miner: move agent logic to worker

* miner: polish

* core: persist block before reorg

5 files changed, 646 insertions, 474 deletions

diff --git a/core/blockchain.go b/core/blockchain.go
index 62dc26125..0461da7fd 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -899,9 +899,7 @@ func (bc *BlockChain) WriteBlockWithState(block *types.Block, receipts []*types.
 	if err := bc.hc.WriteTd(block.Hash(), block.NumberU64(), externTd); err != nil {
 		return NonStatTy, err
 	}
-	// Write other block data using a batch.
-	batch := bc.db.NewBatch()
-	rawdb.WriteBlock(batch, block)
+	rawdb.WriteBlock(bc.db, block)
 
 	root, err := state.Commit(bc.chainConfig.IsEIP158(block.Number()))
 	if err != nil {
@@ -955,6 +953,9 @@ func (bc *BlockChain) WriteBlockWithState(block *types.Block, receipts []*types.
 			}
 		}
 	}
+
+	// Write other block data using a batch.
+	batch := bc.db.NewBatch()
 	rawdb.WriteReceipts(batch, block.Hash(), block.NumberU64(), receipts)
 
 	// If the total difficulty is higher than our known, add it to the canonical chain
diff --git a/miner/agent.go b/miner/agent.go
deleted file mode 100644
index e922ea153..000000000
--- a/miner/agent.go
+++ /dev/null
@@ -1,116 +0,0 @@
-// Copyright 2015 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-package miner
-
-import (
-	"sync"
-	"sync/atomic"
-
-	"github.com/ethereum/go-ethereum/consensus"
-	"github.com/ethereum/go-ethereum/log"
-)
-
-type CpuAgent struct {
-	mu sync.Mutex
-
-	taskCh        chan *Package
-	returnCh      chan<- *Package
-	stop          chan struct{}
-	quitCurrentOp chan struct{}
-
-	chain  consensus.ChainReader
-	engine consensus.Engine
-
-	started int32 // started indicates whether the agent is currently started
-}
-
-func NewCpuAgent(chain consensus.ChainReader, engine consensus.Engine) *CpuAgent {
-	agent := &CpuAgent{
-		chain:  chain,
-		engine: engine,
-		stop:   make(chan struct{}, 1),
-		taskCh: make(chan *Package, 1),
-	}
-	return agent
-}
-
-func (self *CpuAgent) AssignTask(p *Package) {
-	if atomic.LoadInt32(&self.started) == 1 {
-		self.taskCh <- p
-	}
-}
-func (self *CpuAgent) DeliverTo(ch chan<- *Package) { self.returnCh = ch }
-
-func (self *CpuAgent) Start() {
-	if !atomic.CompareAndSwapInt32(&self.started, 0, 1) {
-		return // agent already started
-	}
-	go self.update()
-}
-
-func (self *CpuAgent) Stop() {
-	if !atomic.CompareAndSwapInt32(&self.started, 1, 0) {
-		return // agent already stopped
-	}
-	self.stop <- struct{}{}
-done:
-	// Empty work channel
-	for {
-		select {
-		case <-self.taskCh:
-		default:
-			break done
-		}
-	}
-}
-
-func (self *CpuAgent) update() {
-out:
-	for {
-		select {
-		case p := <-self.taskCh:
-			self.mu.Lock()
-			if self.quitCurrentOp != nil {
-				close(self.quitCurrentOp)
-			}
-			self.quitCurrentOp = make(chan struct{})
-			go self.mine(p, self.quitCurrentOp)
-			self.mu.Unlock()
-		case <-self.stop:
-			self.mu.Lock()
-			if self.quitCurrentOp != nil {
-				close(self.quitCurrentOp)
-				self.quitCurrentOp = nil
-			}
-			self.mu.Unlock()
-			break out
-		}
-	}
-}
-
-func (self *CpuAgent) mine(p *Package, stop <-chan struct{}) {
-	var err error
-	if p.Block, err = self.engine.Seal(self.chain, p.Block, stop); p.Block != nil {
-		log.Info("Successfully sealed new block", "number", p.Block.Number(), "hash", p.Block.Hash())
-		self.returnCh <- p
-	} else {
-		if err != nil {
-			log.Warn("Block sealing failed", "err", err)
-		}
-		self.returnCh <- nil
-	}
-}
diff --git a/miner/miner.go b/miner/miner.go
index 4c5717c8a..e350e456e 100644
--- a/miner/miner.go
+++ b/miner/miner.go
@@ -21,14 +21,12 @@ import (
 	"fmt"
 	"sync/atomic"
 
-	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/consensus"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/eth/downloader"
-	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
@@ -36,10 +34,8 @@ import (
 
 // Backend wraps all methods required for mining.
 type Backend interface {
-	AccountManager() *accounts.Manager
 	BlockChain() *core.BlockChain
 	TxPool() *core.TxPool
-	ChainDb() ethdb.Database
 }
 
 // Miner creates blocks and searches for proof-of-work values.
@@ -49,6 +45,7 @@ type Miner struct {
 	coinbase common.Address
 	eth      Backend
 	engine   consensus.Engine
+	exitCh   chan struct{}
 
 	canStart    int32 // can start indicates whether we can start the mining operation
 	shouldStart int32 // should start indicates whether we should start after sync
@@ -59,10 +56,10 @@ func New(eth Backend, config *params.ChainConfig, mux *event.TypeMux, engine con
 		eth:      eth,
 		mux:      mux,
 		engine:   engine,
+		exitCh:   make(chan struct{}),
 		worker:   newWorker(config, engine, eth, mux),
 		canStart: 1,
 	}
-	miner.Register(NewCpuAgent(eth.BlockChain(), engine))
 	go miner.update()
 
 	return miner
@@ -74,28 +71,35 @@ func New(eth Backend, config *params.ChainConfig, mux *event.TypeMux, engine con
 // and halt your mining operation for as long as the DOS continues.
 func (self *Miner) update() {
 	events := self.mux.Subscribe(downloader.StartEvent{}, downloader.DoneEvent{}, downloader.FailedEvent{})
-out:
-	for ev := range events.Chan() {
-		switch ev.Data.(type) {
-		case downloader.StartEvent:
-			atomic.StoreInt32(&self.canStart, 0)
-			if self.Mining() {
-				self.Stop()
-				atomic.StoreInt32(&self.shouldStart, 1)
-				log.Info("Mining aborted due to sync")
-			}
-		case downloader.DoneEvent, downloader.FailedEvent:
-			shouldStart := atomic.LoadInt32(&self.shouldStart) == 1
+	defer events.Unsubscribe()
 
-			atomic.StoreInt32(&self.canStart, 1)
-			atomic.StoreInt32(&self.shouldStart, 0)
-			if shouldStart {
-				self.Start(self.coinbase)
+	for {
+		select {
+		case ev := <-events.Chan():
+			if ev == nil {
+				return
+			}
+			switch ev.Data.(type) {
+			case downloader.StartEvent:
+				atomic.StoreInt32(&self.canStart, 0)
+				if self.Mining() {
+					self.Stop()
+					atomic.StoreInt32(&self.shouldStart, 1)
+					log.Info("Mining aborted due to sync")
+				}
+			case downloader.DoneEvent, downloader.FailedEvent:
+				shouldStart := atomic.LoadInt32(&self.shouldStart) == 1
+
+				atomic.StoreInt32(&self.canStart, 1)
+				atomic.StoreInt32(&self.shouldStart, 0)
+				if shouldStart {
+					self.Start(self.coinbase)
+				}
+				// stop immediately and ignore all further pending events
+				return
 			}
-			// unsubscribe. we're only interested in this event once
-			events.Unsubscribe()
-			// stop immediately and ignore all further pending events
-			break out
+		case <-self.exitCh:
+			return
 		}
 	}
 }
@@ -109,7 +113,6 @@ func (self *Miner) Start(coinbase common.Address) {
 		return
 	}
 	self.worker.start()
-	self.worker.commitNewWork()
 }
 
 func (self *Miner) Stop() {
@@ -117,12 +120,9 @@ func (self *Miner) Stop() {
 	atomic.StoreInt32(&self.shouldStart, 0)
 }
 
-func (self *Miner) Register(agent Agent) {
-	self.worker.register(agent)
-}
-
-func (self *Miner) Unregister(agent Agent) {
-	self.worker.unregister(agent)
+func (self *Miner) Close() {
+	self.worker.close()
+	close(self.exitCh)
 }
 
 func (self *Miner) Mining() bool {
diff --git a/miner/worker.go b/miner/worker.go
index ae695f019..81a63c29a 100644
--- a/miner/worker.go
+++ b/miner/worker.go
@@ -32,16 +32,14 @@ import (
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
-	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 )
 
 const (
-	resultQueueSize  = 10
-	miningLogAtDepth = 5
-
+	// resultQueueSize is the size of channel listening to sealing result.
+	resultQueueSize = 10
 	// txChanSize is the size of channel listening to NewTxsEvent.
 	// The number is referenced from the size of tx pool.
 	txChanSize = 4096
@@ -49,17 +47,10 @@ const (
 	chainHeadChanSize = 10
 	// chainSideChanSize is the size of channel listening to ChainSideEvent.
 	chainSideChanSize = 10
+	miningLogAtDepth  = 5
 )
 
-// Agent can register themselves with the worker
-type Agent interface {
-	AssignTask(*Package)
-	DeliverTo(chan<- *Package)
-	Start()
-	Stop()
-}
-
-// Env is the workers current environment and holds all of the current state information.
+// Env is the worker's current environment and holds all of the current state information.
 type Env struct {
 	config *params.ChainConfig
 	signer types.Signer
@@ -74,25 +65,124 @@ type Env struct {
 	header   *types.Header
 	txs      []*types.Transaction
 	receipts []*types.Receipt
+}
 
-	createdAt time.Time
+func (env *Env) commitTransaction(tx *types.Transaction, bc *core.BlockChain, coinbase common.Address, gp *core.GasPool) (error, []*types.Log) {
+	snap := env.state.Snapshot()
+
+	receipt, _, err := core.ApplyTransaction(env.config, bc, &coinbase, gp, env.state, env.header, tx, &env.header.GasUsed, vm.Config{})
+	if err != nil {
+		env.state.RevertToSnapshot(snap)
+		return err, nil
+	}
+	env.txs = append(env.txs, tx)
+	env.receipts = append(env.receipts, receipt)
+
+	return nil, receipt.Logs
 }
 
-// Package contains all information for consensus engine sealing and result submitting.
-type Package struct {
-	Receipts []*types.Receipt
-	State    *state.StateDB
-	Block    *types.Block
+func (env *Env) commitTransactions(mux *event.TypeMux, txs *types.TransactionsByPriceAndNonce, bc *core.BlockChain, coinbase common.Address) {
+	if env.gasPool == nil {
+		env.gasPool = new(core.GasPool).AddGas(env.header.GasLimit)
+	}
+
+	var coalescedLogs []*types.Log
+
+	for {
+		// If we don't have enough gas for any further transactions then we're done
+		if env.gasPool.Gas() < params.TxGas {
+			log.Trace("Not enough gas for further transactions", "have", env.gasPool, "want", params.TxGas)
+			break
+		}
+		// Retrieve the next transaction and abort if all done
+		tx := txs.Peek()
+		if tx == nil {
+			break
+		}
+		// Error may be ignored here. The error has already been checked
+		// during transaction acceptance is the transaction pool.
+		//
+		// We use the eip155 signer regardless of the current hf.
+		from, _ := types.Sender(env.signer, tx)
+		// Check whether the tx is replay protected. If we're not in the EIP155 hf
+		// phase, start ignoring the sender until we do.
+		if tx.Protected() && !env.config.IsEIP155(env.header.Number) {
+			log.Trace("Ignoring reply protected transaction", "hash", tx.Hash(), "eip155", env.config.EIP155Block)
+
+			txs.Pop()
+			continue
+		}
+		// Start executing the transaction
+		env.state.Prepare(tx.Hash(), common.Hash{}, env.tcount)
+
+		err, logs := env.commitTransaction(tx, bc, coinbase, env.gasPool)
+		switch err {
+		case core.ErrGasLimitReached:
+			// Pop the current out-of-gas transaction without shifting in the next from the account
+			log.Trace("Gas limit exceeded for current block", "sender", from)
+			txs.Pop()
+
+		case core.ErrNonceTooLow:
+			// New head notification data race between the transaction pool and miner, shift
+			log.Trace("Skipping transaction with low nonce", "sender", from, "nonce", tx.Nonce())
+			txs.Shift()
+
+		case core.ErrNonceTooHigh:
+			// Reorg notification data race between the transaction pool and miner, skip account =
+			log.Trace("Skipping account with hight nonce", "sender", from, "nonce", tx.Nonce())
+			txs.Pop()
+
+		case nil:
+			// Everything ok, collect the logs and shift in the next transaction from the same account
+			coalescedLogs = append(coalescedLogs, logs...)
+			env.tcount++
+			txs.Shift()
+
+		default:
+			// Strange error, discard the transaction and get the next in line (note, the
+			// nonce-too-high clause will prevent us from executing in vain).
+			log.Debug("Transaction failed, account skipped", "hash", tx.Hash(), "err", err)
+			txs.Shift()
+		}
+	}
+
+	if len(coalescedLogs) > 0 || env.tcount > 0 {
+		// make a copy, the state caches the logs and these logs get "upgraded" from pending to mined
+		// logs by filling in the block hash when the block was mined by the local miner. This can
+		// cause a race condition if a log was "upgraded" before the PendingLogsEvent is processed.
+		cpy := make([]*types.Log, len(coalescedLogs))
+		for i, l := range coalescedLogs {
+			cpy[i] = new(types.Log)
+			*cpy[i] = *l
+		}
+		go func(logs []*types.Log, tcount int) {
+			if len(logs) > 0 {
+				mux.Post(core.PendingLogsEvent{Logs: logs})
+			}
+			if tcount > 0 {
+				mux.Post(core.PendingStateEvent{})
+			}
+		}(cpy, env.tcount)
+	}
 }
 
-// worker is the main object which takes care of applying messages to the new state
+// task contains all information for consensus engine sealing and result submitting.
+type task struct {
+	receipts  []*types.Receipt
+	state     *state.StateDB
+	block     *types.Block
+	createdAt time.Time
+}
+
+// worker is the main object which takes care of submitting new work to consensus engine
+// and gathering the sealing result.
 type worker struct {
 	config *params.ChainConfig
 	engine consensus.Engine
+	eth    Backend
+	chain  *core.BlockChain
 
-	mu sync.Mutex
-
-	// update loop
+	// Subscriptions
 	mux          *event.TypeMux
 	txsCh        chan core.NewTxsEvent
 	txsSub       event.Subscription
@@ -101,31 +191,30 @@ type worker struct {
 	chainSideCh  chan core.ChainSideEvent
 	chainSideSub event.Subscription
 
-	agents map[Agent]struct{}
-	recv   chan *Package
+	// Channels
+	newWork  chan struct{}
+	taskCh   chan *task
+	resultCh chan *task
+	exitCh   chan struct{}
 
-	eth     Backend
-	chain   *core.BlockChain
-	proc    core.Validator
-	chainDb ethdb.Database
+	current        *Env                         // An environment for current running cycle.
+	possibleUncles map[common.Hash]*types.Block // A set of side blocks as the possible uncle blocks.
+	unconfirmed    *unconfirmedBlocks           // A set of locally mined blocks pending canonicalness confirmations.
 
+	mu       sync.RWMutex // The lock used to protect the coinbase and extra fields
 	coinbase common.Address
 	extra    []byte
 
-	currentMu sync.Mutex
-	current   *Env
-
-	snapshotMu    sync.RWMutex
+	snapshotMu    sync.RWMutex // The lock used to protect the block snapshot and state snapshot
 	snapshotBlock *types.Block
 	snapshotState *state.StateDB
 
-	uncleMu        sync.Mutex
-	possibleUncles map[common.Hash]*types.Block
-
-	unconfirmed *unconfirmedBlocks // set of locally mined blocks pending canonicalness confirmations
-
 	// atomic status counters
 	running int32 // The indicator whether the consensus engine is running or not.
+
+	// Test hooks
+	newTaskHook      func(*task) // Method to call upon receiving a new sealing task
+	fullTaskInterval func()      // Method to call before pushing the full sealing task
 }
 
 func newWorker(config *params.ChainConfig, engine consensus.Engine, eth Backend, mux *event.TypeMux) *worker {
@@ -134,220 +223,274 @@ func newWorker(config *params.ChainConfig, engine consensus.Engine, eth Backend,
 		engine:         engine,
 		eth:            eth,
 		mux:            mux,
-		txsCh:          make(chan core.NewTxsEvent, txChanSize),
-		chainHeadCh:    make(chan core.ChainHeadEvent, chainHeadChanSize),
-		chainSideCh:    make(chan core.ChainSideEvent, chainSideChanSize),
-		chainDb:        eth.ChainDb(),
-		recv:           make(chan *Package, resultQueueSize),
 		chain:          eth.BlockChain(),
-		proc:           eth.BlockChain().Validator(),
 		possibleUncles: make(map[common.Hash]*types.Block),
-		agents:         make(map[Agent]struct{}),
 		unconfirmed:    newUnconfirmedBlocks(eth.BlockChain(), miningLogAtDepth),
+		txsCh:          make(chan core.NewTxsEvent, txChanSize),
+		chainHeadCh:    make(chan core.ChainHeadEvent, chainHeadChanSize),
+		chainSideCh:    make(chan core.ChainSideEvent, chainSideChanSize),
+		newWork:        make(chan struct{}, 1),
+		taskCh:         make(chan *task),
+		resultCh:       make(chan *task, resultQueueSize),
+		exitCh:         make(chan struct{}),
 	}
 	// Subscribe NewTxsEvent for tx pool
 	worker.txsSub = eth.TxPool().SubscribeNewTxsEvent(worker.txsCh)
 	// Subscribe events for blockchain
 	worker.chainHeadSub = eth.BlockChain().SubscribeChainHeadEvent(worker.chainHeadCh)
 	worker.chainSideSub = eth.BlockChain().SubscribeChainSideEvent(worker.chainSideCh)
-	go worker.update()
 
-	go worker.wait()
-	worker.commitNewWork()
+	go worker.mainLoop()
+	go worker.resultLoop()
+	go worker.taskLoop()
 
+	// Submit first work to initialize pending state.
+	worker.newWork <- struct{}{}
 	return worker
 }
 
-func (self *worker) setEtherbase(addr common.Address) {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	self.coinbase = addr
+// setEtherbase sets the etherbase used to initialize the block coinbase field.
+func (w *worker) setEtherbase(addr common.Address) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	w.coinbase = addr
 }
 
-func (self *worker) setExtra(extra []byte) {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	self.extra = extra
+// setExtra sets the content used to initialize the block extra field.
+func (w *worker) setExtra(extra []byte) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	w.extra = extra
 }
 
-func (self *worker) pending() (*types.Block, *state.StateDB) {
+// 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
-	self.snapshotMu.RLock()
-	defer self.snapshotMu.RUnlock()
-	return self.snapshotBlock, self.snapshotState.Copy()
+	w.snapshotMu.RLock()
+	defer w.snapshotMu.RUnlock()
+	if w.snapshotState == nil {
+		return nil, nil
+	}
+	return w.snapshotBlock, w.snapshotState.Copy()
 }
 
-func (self *worker) pendingBlock() *types.Block {
+// pendingBlock returns pending block.
+func (w *worker) pendingBlock() *types.Block {
 	// return a snapshot to avoid contention on currentMu mutex
-	self.snapshotMu.RLock()
-	defer self.snapshotMu.RUnlock()
-	return self.snapshotBlock
+	w.snapshotMu.RLock()
+	defer w.snapshotMu.RUnlock()
+	return w.snapshotBlock
 }
 
-func (self *worker) start() {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	atomic.StoreInt32(&self.running, 1)
-	for agent := range self.agents {
-		agent.Start()
-	}
+// start sets the running status as 1 and triggers new work submitting.
+func (w *worker) start() {
+	atomic.StoreInt32(&w.running, 1)
+	w.newWork <- struct{}{}
 }
 
-func (self *worker) stop() {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-
-	atomic.StoreInt32(&self.running, 0)
-	for agent := range self.agents {
-		agent.Stop()
-	}
+// stop sets the running status as 0.
+func (w *worker) stop() {
+	atomic.StoreInt32(&w.running, 0)
 }
 
-func (self *worker) isRunning() bool {
-	return atomic.LoadInt32(&self.running) == 1
+// isRunning returns an indicator whether worker is running or not.
+func (w *worker) isRunning() bool {
+	return atomic.LoadInt32(&w.running) == 1
 }
 
-func (self *worker) register(agent Agent) {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	self.agents[agent] = struct{}{}
-	agent.DeliverTo(self.recv)
-	if self.isRunning() {
-		agent.Start()
+// close terminates all background threads maintained by the worker and cleans up buffered channels.
+// Note the worker does not support being closed multiple times.
+func (w *worker) close() {
+	close(w.exitCh)
+	// Clean up buffered channels
+	for empty := false; !empty; {
+		select {
+		case <-w.resultCh:
+		default:
+			empty = true
+		}
 	}
 }
 
-func (self *worker) unregister(agent Agent) {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	delete(self.agents, agent)
-	agent.Stop()
-}
-
-func (self *worker) update() {
-	defer self.txsSub.Unsubscribe()
-	defer self.chainHeadSub.Unsubscribe()
-	defer self.chainSideSub.Unsubscribe()
+// mainLoop is a standalone goroutine to regenerate the sealing task based on the received event.
+func (w *worker) mainLoop() {
+	defer w.txsSub.Unsubscribe()
+	defer w.chainHeadSub.Unsubscribe()
+	defer w.chainSideSub.Unsubscribe()
 
 	for {
-		// A real event arrived, process interesting content
 		select {
-		// Handle ChainHeadEvent
-		case <-self.chainHeadCh:
-			self.commitNewWork()
-
-		// Handle ChainSideEvent
-		case ev := <-self.chainSideCh:
-			self.uncleMu.Lock()
-			self.possibleUncles[ev.Block.Hash()] = ev.Block
-			self.uncleMu.Unlock()
-
-		// Handle NewTxsEvent
-		case ev := <-self.txsCh:
+		case <-w.newWork:
+			// Submit a work when the worker is created or started.
+			w.commitNewWork()
+
+		case <-w.chainHeadCh:
+			// Resubmit a work for new cycle once worker receives chain head event.
+			w.commitNewWork()
+
+		case ev := <-w.chainSideCh:
+			// Add side block to possible uncle block set.
+			w.possibleUncles[ev.Block.Hash()] = ev.Block
+
+		case ev := <-w.txsCh:
 			// Apply transactions to the pending state if we're not mining.
 			//
 			// Note all transactions received may not be continuous with transactions
 			// already included in the current mining block. These transactions will
 			// be automatically eliminated.
-			if !self.isRunning() {
-				self.currentMu.Lock()
+			if !w.isRunning() && w.current != nil {
+				w.mu.Lock()
+				coinbase := w.coinbase
+				w.mu.Unlock()
+
 				txs := make(map[common.Address]types.Transactions)
 				for _, tx := range ev.Txs {
-					acc, _ := types.Sender(self.current.signer, tx)
+					acc, _ := types.Sender(w.current.signer, tx)
 					txs[acc] = append(txs[acc], tx)
 				}
-				txset := types.NewTransactionsByPriceAndNonce(self.current.signer, txs)
-				self.current.commitTransactions(self.mux, txset, self.chain, self.coinbase)
-				self.updateSnapshot()
-				self.currentMu.Unlock()
+				txset := types.NewTransactionsByPriceAndNonce(w.current.signer, txs)
+				w.current.commitTransactions(w.mux, txset, w.chain, coinbase)
+				w.updateSnapshot()
 			} else {
 				// If we're mining, but nothing is being processed, wake on new transactions
-				if self.config.Clique != nil && self.config.Clique.Period == 0 {
-					self.commitNewWork()
+				if w.config.Clique != nil && w.config.Clique.Period == 0 {
+					w.commitNewWork()
 				}
 			}
 
 		// System stopped
-		case <-self.txsSub.Err():
+		case <-w.exitCh:
 			return
-		case <-self.chainHeadSub.Err():
+		case <-w.txsSub.Err():
 			return
-		case <-self.chainSideSub.Err():
+		case <-w.chainHeadSub.Err():
+			return
+		case <-w.chainSideSub.Err():
 			return
 		}
 	}
 }
 
-func (self *worker) wait() {
+// seal pushes a sealing task to consensus engine and submits the result.
+func (w *worker) seal(t *task, stop <-chan struct{}) {
+	var (
+		err error
+		res *task
+	)
+
+	if t.block, err = w.engine.Seal(w.chain, t.block, stop); t.block != nil {
+		log.Info("Successfully sealed new block", "number", t.block.Number(), "hash", t.block.Hash(),
+			"elapsed", common.PrettyDuration(time.Since(t.createdAt)))
+		res = t
+	} else {
+		if err != nil {
+			log.Warn("Block sealing failed", "err", err)
+		}
+		res = nil
+	}
+	select {
+	case w.resultCh <- res:
+	case <-w.exitCh:
+	}
+}
+
+// taskLoop is a standalone goroutine to fetch sealing task from the generator and
+// push them to consensus engine.
+func (w *worker) taskLoop() {
+	var stopCh chan struct{}
+
+	// interrupt aborts the in-flight sealing task.
+	interrupt := func() {
+		if stopCh != nil {
+			close(stopCh)
+			stopCh = nil
+		}
+	}
 	for {
-		for result := range self.recv {
+		select {
+		case task := <-w.taskCh:
+			if w.newTaskHook != nil {
+				w.newTaskHook(task)
+			}
+			interrupt()
+			stopCh = make(chan struct{})
+			go w.seal(task, stopCh)
+		case <-w.exitCh:
+			interrupt()
+			return
+		}
+	}
+}
 
+// resultLoop is a standalone goroutine to handle sealing result submitting
+// and flush relative data to the database.
+func (w *worker) resultLoop() {
+	for {
+		select {
+		case result := <-w.resultCh:
 			if result == nil {
 				continue
 			}
-			block := result.Block
+			block := result.block
 
 			// Update the block hash in all logs since it is now available and not when the
 			// receipt/log of individual transactions were created.
-			for _, r := range result.Receipts {
+			for _, r := range result.receipts {
 				for _, l := range r.Logs {
 					l.BlockHash = block.Hash()
 				}
 			}
-			for _, log := range result.State.Logs() {
+			for _, log := range result.state.Logs() {
 				log.BlockHash = block.Hash()
 			}
-			self.currentMu.Lock()
-			stat, err := self.chain.WriteBlockWithState(block, result.Receipts, result.State)
-			self.currentMu.Unlock()
+			// Commit block and state to database.
+			stat, err := w.chain.WriteBlockWithState(block, result.receipts, result.state)
 			if err != nil {
 				log.Error("Failed writing block to chain", "err", err)
 				continue
 			}
 			// Broadcast the block and announce chain insertion event
-			self.mux.Post(core.NewMinedBlockEvent{Block: block})
+			w.mux.Post(core.NewMinedBlockEvent{Block: block})
 			var (
 				events []interface{}
-				logs   = result.State.Logs()
+				logs   = result.state.Logs()
 			)
-			events = append(events, core.ChainEvent{Block: block, Hash: block.Hash(), Logs: logs})
-			if stat == core.CanonStatTy {
+			switch stat {
+			case core.CanonStatTy:
+				events = append(events, core.ChainEvent{Block: block, Hash: block.Hash(), Logs: logs})
 				events = append(events, core.ChainHeadEvent{Block: block})
+			case core.SideStatTy:
+				events = append(events, core.ChainSideEvent{Block: block})
 			}
-			self.chain.PostChainEvents(events, logs)
+			w.chain.PostChainEvents(events, logs)
 
-			// Insert the block into the set of pending ones to wait for confirmations
-			self.unconfirmed.Insert(block.NumberU64(), block.Hash())
-		}
-	}
-}
+			// Insert the block into the set of pending ones to resultLoop for confirmations
+			w.unconfirmed.Insert(block.NumberU64(), block.Hash())
 
-// push sends a new work task to currently live miner agents.
-func (self *worker) push(p *Package) {
-	for agent := range self.agents {
-		agent.AssignTask(p)
+		case <-w.exitCh:
+			return
+		}
 	}
 }
 
 // makeCurrent creates a new environment for the current cycle.
-func (self *worker) makeCurrent(parent *types.Block, header *types.Header) error {
-	state, err := self.chain.StateAt(parent.Root())
+func (w *worker) makeCurrent(parent *types.Block, header *types.Header) error {
+	state, err := w.chain.StateAt(parent.Root())
 	if err != nil {
 		return err
 	}
 	env := &Env{
-		config:    self.config,
-		signer:    types.NewEIP155Signer(self.config.ChainID),
+		config:    w.config,
+		signer:    types.NewEIP155Signer(w.config.ChainID),
 		state:     state,
 		ancestors: mapset.NewSet(),
 		family:    mapset.NewSet(),
 		uncles:    mapset.NewSet(),
 		header:    header,
-		createdAt: time.Now(),
 	}
 
 	// when 08 is processed ancestors contain 07 (quick block)
-	for _, ancestor := range self.chain.GetBlocksFromHash(parent.Hash(), 7) {
+	for _, ancestor := range w.chain.GetBlocksFromHash(parent.Hash(), 7) {
 		for _, uncle := range ancestor.Uncles() {
 			env.family.Add(uncle.Hash())
 		}
@@ -357,20 +500,63 @@ func (self *worker) makeCurrent(parent *types.Block, header *types.Header) error
 
 	// Keep track of transactions which return errors so they can be removed
 	env.tcount = 0
-	self.current = env
+	w.current = env
 	return nil
 }
 
-func (self *worker) commitNewWork() {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	self.uncleMu.Lock()
-	defer self.uncleMu.Unlock()
-	self.currentMu.Lock()
-	defer self.currentMu.Unlock()
+// commitUncle adds the given block to uncle block set, returns error if failed to add.
+func (w *worker) commitUncle(env *Env, uncle *types.Header) error {
+	hash := uncle.Hash()
+	if env.uncles.Contains(hash) {
+		return fmt.Errorf("uncle not unique")
+	}
+	if !env.ancestors.Contains(uncle.ParentHash) {
+		return fmt.Errorf("uncle's parent unknown (%x)", uncle.ParentHash[0:4])
+	}
+	if env.family.Contains(hash) {
+		return fmt.Errorf("uncle already in family (%x)", hash)
+	}
+	env.uncles.Add(uncle.Hash())
+	return nil
+}
+
+// updateSnapshot updates pending snapshot block and state.
+// Note this function assumes the current variable is thread safe.
+func (w *worker) updateSnapshot() {
+	w.snapshotMu.Lock()
+	defer w.snapshotMu.Unlock()
+
+	var uncles []*types.Header
+	w.current.uncles.Each(func(item interface{}) bool {
+		hash, ok := item.(common.Hash)
+		if !ok {
+			return false
+		}
+		uncle, exist := w.possibleUncles[hash]
+		if !exist {
+			return false
+		}
+		uncles = append(uncles, uncle.Header())
+		return true
+	})
+
+	w.snapshotBlock = types.NewBlock(
+		w.current.header,
+		w.current.txs,
+		uncles,
+		w.current.receipts,
+	)
+
+	w.snapshotState = w.current.state.Copy()
+}
+
+// commitNewWork generates several new sealing tasks based on the parent block.
+func (w *worker) commitNewWork() {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
 
 	tstart := time.Now()
-	parent := self.chain.CurrentBlock()
+	parent := w.chain.CurrentBlock()
 
 	tstamp := tstart.Unix()
 	if parent.Time().Cmp(new(big.Int).SetInt64(tstamp)) >= 0 {
@@ -388,28 +574,28 @@ func (self *worker) commitNewWork() {
 		ParentHash: parent.Hash(),
 		Number:     num.Add(num, common.Big1),
 		GasLimit:   core.CalcGasLimit(parent),
-		Extra:      self.extra,
+		Extra:      w.extra,
 		Time:       big.NewInt(tstamp),
 	}
 	// Only set the coinbase if our consensus engine is running (avoid spurious block rewards)
-	if self.isRunning() {
-		if self.coinbase == (common.Address{}) {
+	if w.isRunning() {
+		if w.coinbase == (common.Address{}) {
 			log.Error("Refusing to mine without etherbase")
 			return
 		}
-		header.Coinbase = self.coinbase
+		header.Coinbase = w.coinbase
 	}
-	if err := self.engine.Prepare(self.chain, header); err != nil {
+	if err := w.engine.Prepare(w.chain, header); err != nil {
 		log.Error("Failed to prepare header for mining", "err", err)
 		return
 	}
 	// If we are care about TheDAO hard-fork check whether to override the extra-data or not
-	if daoBlock := self.config.DAOForkBlock; daoBlock != nil {
+	if daoBlock := w.config.DAOForkBlock; daoBlock != nil {
 		// Check whether the block is among the fork extra-override range
 		limit := new(big.Int).Add(daoBlock, params.DAOForkExtraRange)
 		if header.Number.Cmp(daoBlock) >= 0 && header.Number.Cmp(limit) < 0 {
 			// Depending whether we support or oppose the fork, override differently
-			if self.config.DAOForkSupport {
+			if w.config.DAOForkSupport {
 				header.Extra = common.CopyBytes(params.DAOForkBlockExtra)
 			} else if bytes.Equal(header.Extra, params.DAOForkBlockExtra) {
 				header.Extra = []byte{} // If miner opposes, don't let it use the reserved extra-data
@@ -417,14 +603,14 @@ func (self *worker) commitNewWork() {
 		}
 	}
 	// Could potentially happen if starting to mine in an odd state.
-	err := self.makeCurrent(parent, header)
+	err := w.makeCurrent(parent, header)
 	if err != nil {
 		log.Error("Failed to create mining context", "err", err)
 		return
 	}
 	// Create the current work task and check any fork transitions needed
-	env := self.current
-	if self.config.DAOForkSupport && self.config.DAOForkBlock != nil && self.config.DAOForkBlock.Cmp(header.Number) == 0 {
+	env := w.current
+	if w.config.DAOForkSupport && w.config.DAOForkBlock != nil && w.config.DAOForkBlock.Cmp(header.Number) == 0 {
 		misc.ApplyDAOHardFork(env.state)
 	}
 
@@ -433,11 +619,11 @@ func (self *worker) commitNewWork() {
 		uncles    []*types.Header
 		badUncles []common.Hash
 	)
-	for hash, uncle := range self.possibleUncles {
+	for hash, uncle := range w.possibleUncles {
 		if len(uncles) == 2 {
 			break
 		}
-		if err := self.commitUncle(env, uncle.Header()); err != nil {
+		if err := w.commitUncle(env, uncle.Header()); err != nil {
 			log.Trace("Bad uncle found and will be removed", "hash", hash)
 			log.Trace(fmt.Sprint(uncle))
 
@@ -448,184 +634,73 @@ func (self *worker) commitNewWork() {
 		}
 	}
 	for _, hash := range badUncles {
-		delete(self.possibleUncles, hash)
+		delete(w.possibleUncles, hash)
 	}
 
 	var (
-		emptyBlock *types.Block
-		fullBlock  *types.Block
+		emptyBlock, fullBlock *types.Block
+		emptyState, fullState *state.StateDB
 	)
 
 	// Create an empty block based on temporary copied state for sealing in advance without waiting block
 	// execution finished.
-	emptyState := env.state.Copy()
-	if emptyBlock, err = self.engine.Finalize(self.chain, header, emptyState, nil, uncles, nil); err != nil {
+	emptyState = env.state.Copy()
+	if emptyBlock, err = w.engine.Finalize(w.chain, header, emptyState, nil, uncles, nil); err != nil {
 		log.Error("Failed to finalize block for temporary sealing", "err", err)
 	} else {
 		// Push empty work in advance without applying pending transaction.
 		// The reason is transactions execution can cost a lot and sealer need to
 		// take advantage of this part time.
-		if self.isRunning() {
-			log.Info("Commit new empty mining work", "number", emptyBlock.Number(), "uncles", len(uncles))
-			self.push(&Package{nil, emptyState, emptyBlock})
+		if w.isRunning() {
+			select {
+			case w.taskCh <- &task{receipts: nil, state: emptyState, block: emptyBlock, createdAt: time.Now()}:
+				log.Info("Commit new empty mining work", "number", emptyBlock.Number(), "uncles", len(uncles))
+			case <-w.exitCh:
+				log.Info("Worker has exited")
+				return
+			}
 		}
 	}
 
 	// Fill the block with all available pending transactions.
-	pending, err := self.eth.TxPool().Pending()
+	pending, err := w.eth.TxPool().Pending()
 	if err != nil {
 		log.Error("Failed to fetch pending transactions", "err", err)
 		return
 	}
-	txs := types.NewTransactionsByPriceAndNonce(self.current.signer, pending)
-	env.commitTransactions(self.mux, txs, self.chain, self.coinbase)
+	// Short circuit if there is no available pending transactions
+	if len(pending) == 0 {
+		w.updateSnapshot()
+		return
+	}
+	txs := types.NewTransactionsByPriceAndNonce(w.current.signer, pending)
+	env.commitTransactions(w.mux, txs, w.chain, w.coinbase)
 
 	// Create the full block to seal with the consensus engine
-	if fullBlock, err = self.engine.Finalize(self.chain, header, env.state, env.txs, uncles, env.receipts); err != nil {
+	fullState = env.state.Copy()
+	if fullBlock, err = w.engine.Finalize(w.chain, header, fullState, env.txs, uncles, env.receipts); err != nil {
 		log.Error("Failed to finalize block for sealing", "err", err)
 		return
 	}
-	// We only care about logging if we're actually mining.
-	if self.isRunning() {
-		log.Info("Commit new full mining work", "number", fullBlock.Number(), "txs", env.tcount, "uncles", len(uncles), "elapsed", common.PrettyDuration(time.Since(tstart)))
-		self.unconfirmed.Shift(fullBlock.NumberU64() - 1)
-		self.push(&Package{env.receipts, env.state, fullBlock})
-	}
-	self.updateSnapshot()
-}
-
-func (self *worker) commitUncle(env *Env, uncle *types.Header) error {
-	hash := uncle.Hash()
-	if env.uncles.Contains(hash) {
-		return fmt.Errorf("uncle not unique")
-	}
-	if !env.ancestors.Contains(uncle.ParentHash) {
-		return fmt.Errorf("uncle's parent unknown (%x)", uncle.ParentHash[0:4])
-	}
-	if env.family.Contains(hash) {
-		return fmt.Errorf("uncle already in family (%x)", hash)
-	}
-	env.uncles.Add(uncle.Hash())
-	return nil
-}
-
-func (self *worker) updateSnapshot() {
-	self.snapshotMu.Lock()
-	defer self.snapshotMu.Unlock()
-
-	var uncles []*types.Header
-	self.current.uncles.Each(func(item interface{}) bool {
-		if header, ok := item.(*types.Header); ok {
-			uncles = append(uncles, header)
-			return true
-		}
-		return false
-	})
-
-	self.snapshotBlock = types.NewBlock(
-		self.current.header,
-		self.current.txs,
-		uncles,
-		self.current.receipts,
-	)
-	self.snapshotState = self.current.state.Copy()
-}
-
-func (env *Env) commitTransactions(mux *event.TypeMux, txs *types.TransactionsByPriceAndNonce, bc *core.BlockChain, coinbase common.Address) {
-	if env.gasPool == nil {
-		env.gasPool = new(core.GasPool).AddGas(env.header.GasLimit)
+	// Deep copy receipts here to avoid interaction between different tasks.
+	cpy := make([]*types.Receipt, len(env.receipts))
+	for i, l := range env.receipts {
+		cpy[i] = new(types.Receipt)
+		*cpy[i] = *l
 	}
-
-	var coalescedLogs []*types.Log
-
-	for {
-		// If we don't have enough gas for any further transactions then we're done
-		if env.gasPool.Gas() < params.TxGas {
-			log.Trace("Not enough gas for further transactions", "have", env.gasPool, "want", params.TxGas)
-			break
-		}
-		// Retrieve the next transaction and abort if all done
-		tx := txs.Peek()
-		if tx == nil {
-			break
-		}
-		// Error may be ignored here. The error has already been checked
-		// during transaction acceptance is the transaction pool.
-		//
-		// We use the eip155 signer regardless of the current hf.
-		from, _ := types.Sender(env.signer, tx)
-		// Check whether the tx is replay protected. If we're not in the EIP155 hf
-		// phase, start ignoring the sender until we do.
-		if tx.Protected() && !env.config.IsEIP155(env.header.Number) {
-			log.Trace("Ignoring reply protected transaction", "hash", tx.Hash(), "eip155", env.config.EIP155Block)
-
-			txs.Pop()
-			continue
-		}
-		// Start executing the transaction
-		env.state.Prepare(tx.Hash(), common.Hash{}, env.tcount)
-
-		err, logs := env.commitTransaction(tx, bc, coinbase, env.gasPool)
-		switch err {
-		case core.ErrGasLimitReached:
-			// Pop the current out-of-gas transaction without shifting in the next from the account
-			log.Trace("Gas limit exceeded for current block", "sender", from)
-			txs.Pop()
-
-		case core.ErrNonceTooLow:
-			// New head notification data race between the transaction pool and miner, shift
-			log.Trace("Skipping transaction with low nonce", "sender", from, "nonce", tx.Nonce())
-			txs.Shift()
-
-		case core.ErrNonceTooHigh:
-			// Reorg notification data race between the transaction pool and miner, skip account =
-			log.Trace("Skipping account with hight nonce", "sender", from, "nonce", tx.Nonce())
-			txs.Pop()
-
-		case nil:
-			// Everything ok, collect the logs and shift in the next transaction from the same account
-			coalescedLogs = append(coalescedLogs, logs...)
-			env.tcount++
-			txs.Shift()
-
-		default:
-			// Strange error, discard the transaction and get the next in line (note, the
-			// nonce-too-high clause will prevent us from executing in vain).
-			log.Debug("Transaction failed, account skipped", "hash", tx.Hash(), "err", err)
-			txs.Shift()
+	// We only care about logging if we're actually mining.
+	if w.isRunning() {
+		if w.fullTaskInterval != nil {
+			w.fullTaskInterval()
 		}
-	}
 
-	if len(coalescedLogs) > 0 || env.tcount > 0 {
-		// make a copy, the state caches the logs and these logs get "upgraded" from pending to mined
-		// logs by filling in the block hash when the block was mined by the local miner. This can
-		// cause a race condition if a log was "upgraded" before the PendingLogsEvent is processed.
-		cpy := make([]*types.Log, len(coalescedLogs))
-		for i, l := range coalescedLogs {
-			cpy[i] = new(types.Log)
-			*cpy[i] = *l
+		select {
+		case w.taskCh <- &task{receipts: cpy, state: fullState, block: fullBlock, createdAt: time.Now()}:
+			w.unconfirmed.Shift(fullBlock.NumberU64() - 1)
+			log.Info("Commit new full mining work", "number", fullBlock.Number(), "txs", env.tcount, "uncles", len(uncles), "elapsed", common.PrettyDuration(time.Since(tstart)))
+		case <-w.exitCh:
+			log.Info("Worker has exited")
 		}
-		go func(logs []*types.Log, tcount int) {
-			if len(logs) > 0 {
-				mux.Post(core.PendingLogsEvent{Logs: logs})
-			}
-			if tcount > 0 {
-				mux.Post(core.PendingStateEvent{})
-			}
-		}(cpy, env.tcount)
-	}
-}
-
-func (env *Env) commitTransaction(tx *types.Transaction, bc *core.BlockChain, coinbase common.Address, gp *core.GasPool) (error, []*types.Log) {
-	snap := env.state.Snapshot()
-
-	receipt, _, err := core.ApplyTransaction(env.config, bc, &coinbase, gp, env.state, env.header, tx, &env.header.GasUsed, vm.Config{})
-	if err != nil {
-		env.state.RevertToSnapshot(snap)
-		return err, nil
 	}
-	env.txs = append(env.txs, tx)
-	env.receipts = append(env.receipts, receipt)
-
-	return nil, receipt.Logs
+	w.updateSnapshot()
 }
diff --git a/miner/worker_test.go b/miner/worker_test.go
new file mode 100644
index 000000000..5823a608e
--- /dev/null
+++ b/miner/worker_test.go
@@ -0,0 +1,212 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package miner
+
+import (
+	"math/big"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus"
+	"github.com/ethereum/go-ethereum/consensus/clique"
+	"github.com/ethereum/go-ethereum/consensus/ethash"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/event"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+var (
+	// Test chain configurations
+	testTxPoolConfig  core.TxPoolConfig
+	ethashChainConfig *params.ChainConfig
+	cliqueChainConfig *params.ChainConfig
+
+	// Test accounts
+	testBankKey, _  = crypto.GenerateKey()
+	testBankAddress = crypto.PubkeyToAddress(testBankKey.PublicKey)
+	testBankFunds   = big.NewInt(1000000000000000000)
+
+	acc1Key, _ = crypto.GenerateKey()
+	acc1Addr   = crypto.PubkeyToAddress(acc1Key.PublicKey)
+
+	// Test transactions
+	pendingTxs []*types.Transaction
+	newTxs     []*types.Transaction
+)
+
+func init() {
+	testTxPoolConfig = core.DefaultTxPoolConfig
+	testTxPoolConfig.Journal = ""
+	ethashChainConfig = params.TestChainConfig
+	cliqueChainConfig = params.TestChainConfig
+	cliqueChainConfig.Clique = &params.CliqueConfig{
+		Period: 1,
+		Epoch:  30000,
+	}
+	tx1, _ := types.SignTx(types.NewTransaction(0, acc1Addr, big.NewInt(1000), params.TxGas, nil, nil), types.HomesteadSigner{}, testBankKey)
+	pendingTxs = append(pendingTxs, tx1)
+	tx2, _ := types.SignTx(types.NewTransaction(1, acc1Addr, big.NewInt(1000), params.TxGas, nil, nil), types.HomesteadSigner{}, testBankKey)
+	newTxs = append(newTxs, tx2)
+}
+
+// testWorkerBackend implements worker.Backend interfaces and wraps all information needed during the testing.
+type testWorkerBackend struct {
+	db         ethdb.Database
+	txPool     *core.TxPool
+	chain      *core.BlockChain
+	testTxFeed event.Feed
+}
+
+func newTestWorkerBackend(t *testing.T, chainConfig *params.ChainConfig, engine consensus.Engine) *testWorkerBackend {
+	var (
+		db    = ethdb.NewMemDatabase()
+		gspec = core.Genesis{
+			Config: chainConfig,
+			Alloc:  core.GenesisAlloc{testBankAddress: {Balance: testBankFunds}},
+		}
+	)
+
+	switch engine.(type) {
+	case *clique.Clique:
+		gspec.ExtraData = make([]byte, 32+common.AddressLength+65)
+		copy(gspec.ExtraData[32:], testBankAddress[:])
+	case *ethash.Ethash:
+	default:
+		t.Fatal("unexpect consensus engine type")
+	}
+	gspec.MustCommit(db)
+
+	chain, _ := core.NewBlockChain(db, nil, gspec.Config, engine, vm.Config{})
+	txpool := core.NewTxPool(testTxPoolConfig, chainConfig, chain)
+
+	return &testWorkerBackend{
+		db:     db,
+		chain:  chain,
+		txPool: txpool,
+	}
+}
+
+func (b *testWorkerBackend) BlockChain() *core.BlockChain { return b.chain }
+func (b *testWorkerBackend) TxPool() *core.TxPool         { return b.txPool }
+func (b *testWorkerBackend) PostChainEvents(events []interface{}) {
+	b.chain.PostChainEvents(events, nil)
+}
+
+func newTestWorker(t *testing.T, chainConfig *params.ChainConfig, engine consensus.Engine) (*worker, *testWorkerBackend) {
+	backend := newTestWorkerBackend(t, chainConfig, engine)
+	backend.txPool.AddLocals(pendingTxs)
+	w := newWorker(chainConfig, engine, backend, new(event.TypeMux))
+	w.setEtherbase(testBankAddress)
+	return w, backend
+}
+
+func TestPendingStateAndBlockEthash(t *testing.T) {
+	testPendingStateAndBlock(t, ethashChainConfig, ethash.NewFaker())
+}
+func TestPendingStateAndBlockClique(t *testing.T) {
+	testPendingStateAndBlock(t, cliqueChainConfig, clique.New(cliqueChainConfig.Clique, ethdb.NewMemDatabase()))
+}
+
+func testPendingStateAndBlock(t *testing.T, chainConfig *params.ChainConfig, engine consensus.Engine) {
+	defer engine.Close()
+
+	w, b := newTestWorker(t, chainConfig, engine)
+	defer w.close()
+
+	// Ensure snapshot has been updated.
+	time.Sleep(100 * time.Millisecond)
+	block, state := w.pending()
+	if block.NumberU64() != 1 {
+		t.Errorf("block number mismatch, has %d, want %d", block.NumberU64(), 1)
+	}
+	if balance := state.GetBalance(acc1Addr); balance.Cmp(big.NewInt(1000)) != 0 {
+		t.Errorf("account balance mismatch, has %d, want %d", balance, 1000)
+	}
+	b.txPool.AddLocals(newTxs)
+	// Ensure the new tx events has been processed
+	time.Sleep(100 * time.Millisecond)
+	block, state = w.pending()
+	if balance := state.GetBalance(acc1Addr); balance.Cmp(big.NewInt(2000)) != 0 {
+		t.Errorf("account balance mismatch, has %d, want %d", balance, 2000)
+	}
+}
+
+func TestEmptyWorkEthash(t *testing.T) {
+	testEmptyWork(t, ethashChainConfig, ethash.NewFaker())
+}
+func TestEmptyWorkClique(t *testing.T) {
+	testEmptyWork(t, cliqueChainConfig, clique.New(cliqueChainConfig.Clique, ethdb.NewMemDatabase()))
+}
+
+func testEmptyWork(t *testing.T, chainConfig *params.ChainConfig, engine consensus.Engine) {
+	defer engine.Close()
+
+	w, _ := newTestWorker(t, chainConfig, engine)
+	defer w.close()
+
+	var (
+		taskCh    = make(chan struct{}, 2)
+		taskIndex int
+	)
+
+	checkEqual := func(t *testing.T, task *task, index int) {
+		receiptLen, balance := 0, big.NewInt(0)
+		if index == 1 {
+			receiptLen, balance = 1, big.NewInt(1000)
+		}
+		if len(task.receipts) != receiptLen {
+			t.Errorf("receipt number mismatch has %d, want %d", len(task.receipts), receiptLen)
+		}
+		if task.state.GetBalance(acc1Addr).Cmp(balance) != 0 {
+			t.Errorf("account balance mismatch has %d, want %d", task.state.GetBalance(acc1Addr), balance)
+		}
+	}
+
+	w.newTaskHook = func(task *task) {
+		if task.block.NumberU64() == 1 {
+			checkEqual(t, task, taskIndex)
+			taskIndex += 1
+			taskCh <- struct{}{}
+		}
+	}
+	w.fullTaskInterval = func() {
+		time.Sleep(100 * time.Millisecond)
+	}
+
+	// Ensure worker has finished initialization
+	for {
+		b := w.pendingBlock()
+		if b != nil && b.NumberU64() == 1 {
+			break
+		}
+	}
+
+	w.start()
+	for i := 0; i < 2; i += 1 {
+		to := time.NewTimer(time.Second)
+		select {
+		case <-taskCh:
+		case <-to.C:
+			t.Error("new task timeout")
+		}
+	}
+}