diff --git a/cmd/geth/consolecmd_test.go b/cmd/geth/consolecmd_test.go
index 8d8b10f8fa..34ba877020 100644
--- a/cmd/geth/consolecmd_test.go
+++ b/cmd/geth/consolecmd_test.go
@@ -31,7 +31,7 @@ import (
 )
 
 const (
-	ipcAPIs  = "admin:1.0 debug:1.0 eth:1.0 miner:1.0 net:1.0 personal:1.0 rpc:1.0 shh:1.0 txpool:1.0 web3:1.0"
+	ipcAPIs  = "admin:1.0 debug:1.0 eth:1.0 ethash:1.0 miner:1.0 net:1.0 personal:1.0 rpc:1.0 shh:1.0 txpool:1.0 web3:1.0"
 	httpAPIs = "eth:1.0 net:1.0 rpc:1.0 web3:1.0"
 )
 
diff --git a/consensus/clique/clique.go b/consensus/clique/clique.go
index 8968f500f1..5963900c97 100644
--- a/consensus/clique/clique.go
+++ b/consensus/clique/clique.go
@@ -672,6 +672,11 @@ func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
 	return new(big.Int).Set(diffNoTurn)
 }
 
+// Close implements consensus.Engine, returning internal error and close the clique.
+func (c *Clique) Close() error {
+	return nil
+}
+
 // APIs implements consensus.Engine, returning the user facing RPC API to allow
 // controlling the signer voting.
 func (c *Clique) APIs(chain consensus.ChainReader) []rpc.API {
diff --git a/consensus/consensus.go b/consensus/consensus.go
index 5774af1a78..ae0fefb490 100644
--- a/consensus/consensus.go
+++ b/consensus/consensus.go
@@ -96,6 +96,9 @@ type Engine interface {
 
 	// APIs returns the RPC APIs this consensus engine provides.
 	APIs(chain ChainReader) []rpc.API
+
+	// Close closes the consensus engine.
+	Close() error
 }
 
 // PoW is a consensus engine based on proof-of-work.
diff --git a/consensus/ethash/algorithm_test.go b/consensus/ethash/algorithm_test.go
index f0c6465fdb..e7625f7c00 100644
--- a/consensus/ethash/algorithm_test.go
+++ b/consensus/ethash/algorithm_test.go
@@ -730,6 +730,7 @@ func TestConcurrentDiskCacheGeneration(t *testing.T) {
 		go func(idx int) {
 			defer pend.Done()
 			ethash := New(Config{cachedir, 0, 1, "", 0, 0, ModeNormal})
+			defer ethash.Close()
 			if err := ethash.VerifySeal(nil, block.Header()); err != nil {
 				t.Errorf("proc %d: block verification failed: %v", idx, err)
 			}
diff --git a/consensus/ethash/api.go b/consensus/ethash/api.go
index fb64b85d07..2e5c2c8f2d 100644
--- a/consensus/ethash/api.go
+++ b/consensus/ethash/api.go
@@ -13,78 +13,87 @@
 //
 // 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 ethash
 
 import (
-	"time"
+	"errors"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/types"
 )
 
-// API exposes ethash related methods for the RPC interface
+var errEthashStopped = errors.New("ethash stopped")
+
+// API exposes ethash related methods for the RPC interface.
 type API struct {
 	ethash *Ethash
 }
 
-// GetWork returns a work package for external miner. The work package consists of 3 strings
-// result[0], 32 bytes hex encoded current block header pow-hash
-// result[1], 32 bytes hex encoded seed hash used for DAG
-// result[2], 32 bytes hex encoded boundary condition ("target"), 2^256/difficulty
-func (s *API) GetWork() ([3]string, error) {
+// GetWork returns a work package for external miner.
+//
+// The work package consists of 3 strings:
+//   result[0] - 32 bytes hex encoded current block header pow-hash
+//   result[1] - 32 bytes hex encoded seed hash used for DAG
+//   result[2] - 32 bytes hex encoded boundary condition ("target"), 2^256/difficulty
+func (api *API) GetWork() ([3]string, error) {
 	var (
-		workCh = make(chan [3]string)
-		errCh  = make(chan error)
+		workCh = make(chan [3]string, 1)
+		errCh  = make(chan error, 1)
+		err    error
 	)
-	op := &remoteOp{
-		typ:    opGetWork,
-		workCh: workCh,
-		errCh:  errCh,
+
+	select {
+	case api.ethash.fetchWorkCh <- &sealWork{errCh: errCh, resCh: workCh}:
+	case <-api.ethash.exitCh:
+		return [3]string{}, errEthashStopped
 	}
-	s.ethash.remoteOp <- op
-	if err := <-errCh; err == nil {
+
+	if err = <-errCh; err == nil {
 		return <-workCh, nil
-	} else {
-		return [3]string{}, err
 	}
+	return [3]string{}, err
 }
 
-// SubmitWork can be used by external miner to submit their POW solution. It returns an indication if the work was
-// accepted. Note, this is not an indication if the provided work was valid!
-func (s *API) SubmitWork(nonce types.BlockNonce, solution, digest common.Hash) bool {
-	var errCh = make(chan error)
-	op := &remoteOp{
-		typ: opSubmitWork,
-		result: mineResult{
-			nonce:     nonce,
-			mixDigest: digest,
-			hash:      solution,
-		},
-		errCh: errCh,
-	}
-	s.ethash.remoteOp <- op
-	if err := <-errCh; err == nil {
-		return true
-	} else {
+// SubmitWork can be used by external miner to submit their POW solution.
+// It returns an indication if the work was accepted.
+// Note either an invalid solution, a stale work a non-existent work will return false.
+func (api *API) SubmitWork(nonce types.BlockNonce, hash, digest common.Hash) bool {
+	var errCh = make(chan error, 1)
+
+	select {
+	case api.ethash.submitWorkCh <- &mineResult{
+		nonce:     nonce,
+		mixDigest: digest,
+		hash:      hash,
+		errCh:     errCh,
+	}:
+	case <-api.ethash.exitCh:
 		return false
 	}
+
+	err := <-errCh
+	return err == nil
 }
 
-// SubmitHashrate can be used for remote miners to submit their hash rate. This enables the node to report the combined
-// hash rate of all miners which submit work through this node. It accepts the miner hash rate and an identifier which
-// must be unique between nodes.
-func (s *API) SubmitHashRate(r hexutil.Uint64, id common.Hash) bool {
-	submit := func(rate map[common.Hash]hashrate) {
-		rate[id] = hashrate{rate: uint64(r), ping: time.Now()}
+// SubmitHashrate can be used for remote miners to submit their hash rate.
+// This enables the node to report the combined hash rate of all miners
+// which submit work through this node.
+//
+// It accepts the miner hash rate and an identifier which must be unique
+// between nodes.
+func (api *API) SubmitHashRate(rate hexutil.Uint64, id common.Hash) bool {
+	var doneCh = make(chan struct{}, 1)
+
+	select {
+	case api.ethash.submitRateCh <- &hashrate{done: doneCh, rate: uint64(rate), id: id}:
+	case <-api.ethash.exitCh:
+		return false
 	}
-	errCh := make(chan error)
-	op := &remoteOp{
-		typ:    opHashrate,
-		rateOp: submit,
-		errCh:  errCh,
-	}
-	s.ethash.remoteOp <- op
-	<-errCh
+
+	// Block until hash rate submitted successfully.
+	<-doneCh
+
 	return true
 }
diff --git a/consensus/ethash/ethash.go b/consensus/ethash/ethash.go
index 2fccc57734..424f779917 100644
--- a/consensus/ethash/ethash.go
+++ b/consensus/ethash/ethash.go
@@ -391,38 +391,28 @@ type Config struct {
 	PowMode        Mode
 }
 
-// remoteOpType defines all the types of operations related to remote sealer.
-type remoteOpType uint
-
-const (
-	opGetWork remoteOpType = iota
-	opSubmitWork
-	opHashrate
-)
-
 // mineResult wraps the pow solution parameters for the specified block.
 type mineResult struct {
 	nonce     types.BlockNonce
 	mixDigest common.Hash
 	hash      common.Hash
+
+	errCh chan error
 }
 
+// hashrate wraps the hash rate submitted by the remote sealer.
 type hashrate struct {
 	id   common.Hash
 	ping time.Time
 	rate uint64
+
+	done chan struct{}
 }
 
-type hashrateOp func(map[common.Hash]hashrate)
-
-// remoteOp wraps a mining operation sent by remote miner.
-type remoteOp struct {
-	typ    remoteOpType
-	result mineResult
-	errCh  chan error
-	workCh chan [3]string
-
-	rateOp hashrateOp
+// sealWork wraps a seal work package for remote sealer.
+type sealWork struct {
+	errCh chan error
+	resCh chan [3]string
 }
 
 // Ethash is a consensus engine based on proof-of-work implementing the ethash
@@ -433,8 +423,6 @@ type Ethash struct {
 	caches   *lru // In memory caches to avoid regenerating too often
 	datasets *lru // In memory datasets to avoid regenerating too often
 
-	exitCh chan struct{} // Notification channel to exiting backend threads
-
 	// Mining related fields
 	rand     *rand.Rand    // Properly seeded random source for nonces
 	threads  int           // Number of threads to mine on if mining
@@ -442,15 +430,21 @@ type Ethash struct {
 	hashrate metrics.Meter // Meter tracking the average hashrate
 
 	// Remote sealer related fields
-	workCh   chan *types.Block // Notification channel to push new work to remote sealer
-	resultCh chan *types.Block // Channel used by mining threads to return result
-	remoteOp chan *remoteOp    // Channel used to receive all mining operations from api
+	workCh       chan *types.Block // Notification channel to push new work to remote sealer
+	resultCh     chan *types.Block // Channel used by mining threads to return result
+	fetchWorkCh  chan *sealWork    // Channel used for remote sealer to fetch mining work
+	submitWorkCh chan *mineResult  // Channel used for remote sealer to submit their mining result
+	fetchRateCh  chan chan uint64  // Channel used to gather submitted hash rate for local or remote sealer.
+	submitRateCh chan *hashrate    // Channel used for remote sealer to submit their mining hashrate
+
 	// The fields below are hooks for testing
 	shared    *Ethash       // Shared PoW verifier to avoid cache regeneration
 	fakeFail  uint64        // Block number which fails PoW check even in fake mode
 	fakeDelay time.Duration // Time delay to sleep for before returning from verify
 
-	lock sync.Mutex // Ensures thread safety for the in-memory caches and mining fields
+	lock      sync.Mutex      // Ensures thread safety for the in-memory caches and mining fields
+	closeOnce sync.Once       // Ensures exit channel will not be closed twice.
+	exitCh    chan chan error // Notification channel to exiting backend threads
 }
 
 // New creates a full sized ethash PoW scheme.
@@ -466,18 +460,20 @@ func New(config Config) *Ethash {
 		log.Info("Disk storage enabled for ethash DAGs", "dir", config.DatasetDir, "count", config.DatasetsOnDisk)
 	}
 	ethash := &Ethash{
-		config:   config,
-		caches:   newlru("cache", config.CachesInMem, newCache),
-		datasets: newlru("dataset", config.DatasetsInMem, newDataset),
-		update:   make(chan struct{}),
-		hashrate: metrics.NewMeter(),
-		exitCh:   make(chan struct{}),
-		workCh:   make(chan *types.Block),
-		resultCh: make(chan *types.Block),
-		remoteOp: make(chan *remoteOp),
+		config:       config,
+		caches:       newlru("cache", config.CachesInMem, newCache),
+		datasets:     newlru("dataset", config.DatasetsInMem, newDataset),
+		update:       make(chan struct{}),
+		hashrate:     metrics.NewMeter(),
+		workCh:       make(chan *types.Block),
+		resultCh:     make(chan *types.Block),
+		fetchWorkCh:  make(chan *sealWork),
+		submitWorkCh: make(chan *mineResult),
+		fetchRateCh:  make(chan chan uint64),
+		submitRateCh: make(chan *hashrate),
+		exitCh:       make(chan chan error),
 	}
-	go ethash.remote(ethash.resultCh)
-	runtime.SetFinalizer(ethash, (*Ethash).close)
+	go ethash.remote()
 	return ethash
 }
 
@@ -485,18 +481,20 @@ func New(config Config) *Ethash {
 // purposes.
 func NewTester() *Ethash {
 	ethash := &Ethash{
-		config: Config{PowMode: ModeTest},
-		caches:   newlru("cache", 1, newCache),
-		datasets: newlru("dataset", 1, newDataset),
-		update:   make(chan struct{}),
-		hashrate: metrics.NewMeter(),
-		exitCh:   make(chan struct{}),
-		workCh:   make(chan *types.Block),
-		resultCh: make(chan *types.Block),
-		remoteOp: make(chan *remoteOp),
+		config:       Config{PowMode: ModeTest},
+		caches:       newlru("cache", 1, newCache),
+		datasets:     newlru("dataset", 1, newDataset),
+		update:       make(chan struct{}),
+		hashrate:     metrics.NewMeter(),
+		workCh:       make(chan *types.Block),
+		resultCh:     make(chan *types.Block),
+		fetchWorkCh:  make(chan *sealWork),
+		submitWorkCh: make(chan *mineResult),
+		fetchRateCh:  make(chan chan uint64),
+		submitRateCh: make(chan *hashrate),
+		exitCh:       make(chan chan error),
 	}
-	go ethash.remote(ethash.resultCh)
-	runtime.SetFinalizer(ethash, (*Ethash).close)
+	go ethash.remote()
 	return ethash
 }
 
@@ -508,6 +506,7 @@ func NewFaker() *Ethash {
 		config: Config{
 			PowMode: ModeFake,
 		},
+		exitCh: make(chan chan error),
 	}
 }
 
@@ -520,6 +519,7 @@ func NewFakeFailer(fail uint64) *Ethash {
 			PowMode: ModeFake,
 		},
 		fakeFail: fail,
+		exitCh:   make(chan chan error),
 	}
 }
 
@@ -532,6 +532,7 @@ func NewFakeDelayer(delay time.Duration) *Ethash {
 			PowMode: ModeFake,
 		},
 		fakeDelay: delay,
+		exitCh:    make(chan chan error),
 	}
 }
 
@@ -542,19 +543,32 @@ func NewFullFaker() *Ethash {
 		config: Config{
 			PowMode: ModeFullFake,
 		},
+		exitCh: make(chan chan error),
 	}
 }
 
 // NewShared creates a full sized ethash PoW shared between all requesters running
 // in the same process.
 func NewShared() *Ethash {
-	return &Ethash{shared: sharedEthash}
+	return &Ethash{
+		shared: sharedEthash,
+		exitCh: make(chan chan error),
+	}
 }
 
-// close closes the exit channel to notify all backend threads exiting.
-func (ethash *Ethash) close() {
-	runtime.SetFinalizer(ethash, nil)
-	close(ethash.exitCh)
+// Close closes the exit channel to notify all backend threads exiting.
+func (ethash *Ethash) Close() error {
+	var err error
+	ethash.closeOnce.Do(func() {
+		var errCh = make(chan error)
+		select {
+		case ethash.exitCh <- errCh:
+			err = <-errCh
+			close(ethash.exitCh)
+		default:
+		}
+	})
+	return err
 }
 
 // cache tries to retrieve a verification cache for the specified block number
@@ -632,37 +646,38 @@ func (ethash *Ethash) SetThreads(threads int) {
 // Note the returned hashrate includes local hashrate, but also includes the total
 // hashrate of all remote miner.
 func (ethash *Ethash) Hashrate() float64 {
-	var (
-		total uint64
-		errCh = make(chan error)
-	)
-	// getHashrate gathers all remote miner's hashrate.
-	getHashrate := func(hashrate map[common.Hash]hashrate) {
-		for _, rate := range hashrate {
-			// this could overflow
-			total += rate.rate
-		}
-		return
-	}
-	op := &remoteOp{
-		typ:    opHashrate,
-		rateOp: getHashrate,
-		errCh:  errCh,
-	}
-	ethash.remoteOp <- op
-	<-errCh
+	var resCh = make(chan uint64, 1)
 
+	select {
+	case ethash.fetchRateCh <- resCh:
+	case <-ethash.exitCh:
+		// Return local hashrate only if ethash is stopped.
+		return ethash.hashrate.Rate1()
+	}
+
+	// Gather total submitted hash rate of remote sealers.
+	total := <-resCh
 	return ethash.hashrate.Rate1() + float64(total)
 }
 
 // APIs implements consensus.Engine, returning the user facing RPC APIs.
 func (ethash *Ethash) APIs(chain consensus.ChainReader) []rpc.API {
-	return []rpc.API{{
-		Namespace: "eth",
-		Version:   "1.0",
-		Service:   &API{ethash},
-		Public:    true,
-	}}
+	// In order to ensure backward compatibility, we exposes ethash RPC APIs
+	// to both eth and ethash namespaces.
+	return []rpc.API{
+		{
+			Namespace: "eth",
+			Version:   "1.0",
+			Service:   &API{ethash},
+			Public:    true,
+		},
+		{
+			Namespace: "ethash",
+			Version:   "1.0",
+			Service:   &API{ethash},
+			Public:    true,
+		},
+	}
 }
 
 // SeedHash is the seed to use for generating a verification cache and the mining
diff --git a/consensus/ethash/ethash_test.go b/consensus/ethash/ethash_test.go
index b5d8ae9022..ccdd30fb0f 100644
--- a/consensus/ethash/ethash_test.go
+++ b/consensus/ethash/ethash_test.go
@@ -23,6 +23,7 @@ import (
 	"os"
 	"sync"
 	"testing"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
@@ -34,6 +35,7 @@ func TestTestMode(t *testing.T) {
 	head := &types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(100)}
 
 	ethash := NewTester()
+	defer ethash.Close()
 	block, err := ethash.Seal(nil, types.NewBlockWithHeader(head), nil)
 	if err != nil {
 		t.Fatalf("failed to seal block: %v", err)
@@ -54,6 +56,7 @@ func TestCacheFileEvict(t *testing.T) {
 	}
 	defer os.RemoveAll(tmpdir)
 	e := New(Config{CachesInMem: 3, CachesOnDisk: 10, CacheDir: tmpdir, PowMode: ModeTest})
+	defer e.Close()
 
 	workers := 8
 	epochs := 100
@@ -71,7 +74,7 @@ func verifyTest(wg *sync.WaitGroup, e *Ethash, workerIndex, epochs int) {
 	const wiggle = 4 * epochLength
 	r := rand.New(rand.NewSource(int64(workerIndex)))
 	for epoch := 0; epoch < epochs; epoch++ {
-		block := int64(epoch) * epochLength - wiggle / 2 + r.Int63n(wiggle)
+		block := int64(epoch)*epochLength - wiggle/2 + r.Int63n(wiggle)
 		if block < 0 {
 			block = 0
 		}
@@ -82,14 +85,16 @@ func verifyTest(wg *sync.WaitGroup, e *Ethash, workerIndex, epochs int) {
 
 func TestRemoteSealer(t *testing.T) {
 	ethash := NewTester()
+	defer ethash.Close()
 	api := &API{ethash}
-	if _, err := api.GetWork(); err != errNoMineWork {
-		t.Error("expected to return an error indicate there is no mining work")
+	if _, err := api.GetWork(); err != errNoMiningWork {
+		t.Error("expect to return an error indicate there is no mining work")
 	}
 
 	head := &types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(100)}
 	block := types.NewBlockWithHeader(head)
-	// Push new work
+
+	// Push new work.
 	ethash.Seal(nil, block, nil)
 
 	var (
@@ -97,11 +102,29 @@ func TestRemoteSealer(t *testing.T) {
 		err  error
 	)
 	if work, err = api.GetWork(); err != nil || work[0] != block.HashNoNonce().Hex() {
-		t.Error("expected to return a mining work has same hash")
+		t.Error("expect to return a mining work has same hash")
 	}
 
 	if res := api.SubmitWork(types.BlockNonce{}, block.HashNoNonce(), common.Hash{}); res {
-		t.Error("expected to return false when submit a fake solution")
+		t.Error("expect to return false when submit a fake solution")
+	}
+
+	// Push new block with same block number to replace the original one.
+	head = &types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(1000)}
+	block = types.NewBlockWithHeader(head)
+	ethash.Seal(nil, block, nil)
+
+	if work, err = api.GetWork(); err != nil || work[0] != block.HashNoNonce().Hex() {
+		t.Error("expect to return the latest pushed work")
+	}
+
+	// Push block with higher block number.
+	newHead := &types.Header{Number: big.NewInt(2), Difficulty: big.NewInt(100)}
+	newBlock := types.NewBlockWithHeader(newHead)
+	ethash.Seal(nil, newBlock, nil)
+
+	if res := api.SubmitWork(types.BlockNonce{}, block.HashNoNonce(), common.Hash{}); res {
+		t.Error("expect to return false when submit a stale solution")
 	}
 }
 
@@ -113,6 +136,13 @@ func TestHashRate(t *testing.T) {
 		expect   uint64
 		ids      = []common.Hash{common.HexToHash("a"), common.HexToHash("b"), common.HexToHash("c")}
 	)
+
+	defer ethash.Close()
+
+	if tot := ethash.Hashrate(); tot != 0 {
+		t.Error("expect the result should be zero")
+	}
+
 	for i := 0; i < len(hashrate); i += 1 {
 		if res := api.SubmitHashRate(hashrate[i], ids[i]); !res {
 			t.Error("remote miner submit hashrate failed")
@@ -123,3 +153,19 @@ func TestHashRate(t *testing.T) {
 		t.Error("expect total hashrate should be same")
 	}
 }
+
+func TestClosedRemoteSealer(t *testing.T) {
+	ethash := NewTester()
+	// Make sure exit channel has been listened
+	time.Sleep(1 * time.Second)
+	ethash.Close()
+
+	api := &API{ethash}
+	if _, err := api.GetWork(); err != errEthashStopped {
+		t.Error("expect to return an error to indicate ethash is stopped")
+	}
+
+	if res := api.SubmitHashRate(hexutil.Uint64(100), common.HexToHash("a")); res {
+		t.Error("expect to return false when submit hashrate to a stopped ethash")
+	}
+}
diff --git a/consensus/ethash/sealer.go b/consensus/ethash/sealer.go
index 4d34f78cf7..a843fab672 100644
--- a/consensus/ethash/sealer.go
+++ b/consensus/ethash/sealer.go
@@ -33,9 +33,8 @@ import (
 )
 
 var (
-	errNoMineWork        = errors.New("No mining work available yet, don't panic.")
-	errInvalidSealResult = errors.New("Invalid or stale proof-of-work solution.")
-	errUndefinedRemoteOp = errors.New("Undefined remote mining operation.")
+	errNoMiningWork      = errors.New("no mining work available yet, don't panic")
+	errInvalidSealResult = errors.New("invalid or stale proof-of-work solution")
 )
 
 // Seal implements consensus.Engine, attempting to find a nonce that satisfies
@@ -51,7 +50,6 @@ func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop
 	if ethash.shared != nil {
 		return ethash.shared.Seal(chain, block, stop)
 	}
-
 	// Create a runner and the multiple search threads it directs
 	abort := make(chan struct{})
 
@@ -72,10 +70,10 @@ func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop
 	if threads < 0 {
 		threads = 0 // Allows disabling local mining without extra logic around local/remote
 	}
-
 	// Push new work to remote sealer
-	ethash.workCh <- block
-
+	if ethash.workCh != nil {
+		ethash.workCh <- block
+	}
 	var pend sync.WaitGroup
 	for i := 0; i < threads; i++ {
 		pend.Add(1)
@@ -164,61 +162,72 @@ search:
 }
 
 // remote starts a standalone goroutine to handle remote mining related stuff.
-func (ethash *Ethash) remote(resultCh chan *types.Block) {
+func (ethash *Ethash) remote() {
 	var (
 		works       = make(map[common.Hash]*types.Block)
-		hashrate    = make(map[common.Hash]hashrate)
+		rates       = make(map[common.Hash]hashrate)
 		currentWork *types.Block
 	)
 
-	// getWork returns a work package for external miner. The work package consists of 3 strings
-	// result[0], 32 bytes hex encoded current block header pow-hash
-	// result[1], 32 bytes hex encoded seed hash used for DAG
-	// result[2], 32 bytes hex encoded boundary condition ("target"), 2^256/difficulty
+	// getWork returns a work package for external miner.
+	//
+	// The work package consists of 3 strings:
+	//   result[0], 32 bytes hex encoded current block header pow-hash
+	//   result[1], 32 bytes hex encoded seed hash used for DAG
+	//   result[2], 32 bytes hex encoded boundary condition ("target"), 2^256/difficulty
 	getWork := func() ([3]string, error) {
 		var res [3]string
 		if currentWork == nil {
-			return res, errNoMineWork
+			return res, errNoMiningWork
 		}
 		res[0] = currentWork.HashNoNonce().Hex()
 		res[1] = common.BytesToHash(SeedHash(currentWork.NumberU64())).Hex()
-		// Calculate the "target" to be returned to the external sealer
+
+		// Calculate the "target" to be returned to the external sealer.
 		n := big.NewInt(1)
 		n.Lsh(n, 255)
 		n.Div(n, currentWork.Difficulty())
 		n.Lsh(n, 1)
 		res[2] = common.BytesToHash(n.Bytes()).Hex()
+
+		// Trace the seal work fetched by remote sealer.
 		works[currentWork.HashNoNonce()] = currentWork
 		return res, nil
 	}
 
 	// submitWork verifies the submitted pow solution, returning
 	// whether the solution was accepted or not (not can be both a bad pow as well as
-	// any other error, like no work pending).
-	submitWork := func(result mineResult) bool {
+	// any other error, like no pending work or stale mining result).
+	submitWork := func(nonce types.BlockNonce, mixDigest common.Hash, hash common.Hash) bool {
 		// Make sure the work submitted is present
-		block := works[result.hash]
+		block := works[hash]
 		if block == nil {
-			log.Info("Work submitted but none pending", "hash", result.hash)
+			log.Info("Work submitted but none pending", "hash", hash)
 			return false
 		}
-		// Make sure the Engine solutions is indeed valid
+
+		// Verify the correctness of submitted result.
 		header := block.Header()
-		header.Nonce = result.nonce
-		header.MixDigest = result.mixDigest
-
+		header.Nonce = nonce
+		header.MixDigest = mixDigest
 		if err := ethash.VerifySeal(nil, header); err != nil {
-			log.Warn("Invalid proof-of-work submitted", "hash", result.hash, "err", err)
+			log.Warn("Invalid proof-of-work submitted", "hash", hash, "err", err)
 			return false
 		}
 
-		// Solutions seems to be valid, return to the miner and notify acceptance
+		// Make sure the result channel is created.
+		if ethash.resultCh == nil {
+			log.Warn("Ethash result channel is empty, submitted mining result is rejected")
+			return false
+		}
+
+		// Solutions seems to be valid, return to the miner and notify acceptance.
 		select {
-		case resultCh <- block.WithSeal(header):
-			delete(works, result.hash)
+		case ethash.resultCh <- block.WithSeal(header):
+			delete(works, hash)
 			return true
 		default:
-			log.Info("Work submitted is stale", "hash", result.hash)
+			log.Info("Work submitted is stale", "hash", hash)
 			return false
 		}
 	}
@@ -234,48 +243,53 @@ running:
 				// Start new round mining, throw out all previous work.
 				works = make(map[common.Hash]*types.Block)
 			}
-			// Update current work with new received block
+			// Update current work with new received block.
 			// Note same work can be past twice, happens when changing CPU threads.
 			currentWork = block
 
-		case op := <-ethash.remoteOp:
-			switch op.typ {
-			case opGetWork:
-				// Return current mining work to remote miner
-				work, err := getWork()
-				if err != nil {
-					op.errCh <- err
-				} else {
-					close(op.errCh)
-					op.workCh <- work
-				}
-			case opSubmitWork:
-				// Verify submitted PoW solution based on maintained mining blocks
-				if submitWork(op.result) {
-					close(op.errCh)
-				} else {
-					op.errCh <- errInvalidSealResult
-				}
-			case opHashrate:
-				// This case is used by remote miner hashrate operation
-				if op.rateOp != nil {
-					op.rateOp(hashrate)
-					close(op.errCh)
-				}
-			default:
-				op.errCh <- errUndefinedRemoteOp
+		case work := <-ethash.fetchWorkCh:
+			// Return current mining work to remote miner.
+			miningWork, err := getWork()
+			if err != nil {
+				work.errCh <- err
+			} else {
+				close(work.errCh)
+				work.resCh <- miningWork
 			}
 
+		case result := <-ethash.submitWorkCh:
+			// Verify submitted PoW solution based on maintained mining blocks.
+			if submitWork(result.nonce, result.mixDigest, result.hash) {
+				close(result.errCh)
+			} else {
+				result.errCh <- errInvalidSealResult
+			}
+
+		case result := <-ethash.submitRateCh:
+			// Trace remote sealer's hash rate by submitted value.
+			rates[result.id] = hashrate{rate: result.rate, ping: time.Now()}
+			close(result.done)
+
+		case req := <-ethash.fetchRateCh:
+			// Gather all hash rate submitted by remote sealer.
+			var total uint64
+			for _, rate := range rates {
+				// this could overflow
+				total += rate.rate
+			}
+			req <- total
+
 		case <-ticker.C:
-			// Clear stale submited hashrate
-			for id, rate := range hashrate {
+			// Clear stale submitted hash rate.
+			for id, rate := range rates {
 				if time.Since(rate.ping) > 10*time.Second {
-					delete(hashrate, id)
+					delete(rates, id)
 				}
 			}
 
-		case <-ethash.exitCh:
-			// Exit remote loop if ethash object is cleared by GC
+		case errCh := <-ethash.exitCh:
+			// Exit remote loop if ethash is closed and return relevant error.
+			errCh <- nil
 			break running
 		}
 	}
diff --git a/eth/backend.go b/eth/backend.go
index a18abdfb56..62a85f3fcb 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -411,6 +411,7 @@ func (s *Ethereum) Start(srvr *p2p.Server) error {
 func (s *Ethereum) Stop() error {
 	s.bloomIndexer.Close()
 	s.blockchain.Stop()
+	s.engine.Close()
 	s.protocolManager.Stop()
 	if s.lesServer != nil {
 		s.lesServer.Stop()
@@ -421,6 +422,5 @@ func (s *Ethereum) Stop() error {
 
 	s.chainDb.Close()
 	close(s.shutdownChan)
-
 	return nil
 }
diff --git a/internal/web3ext/web3ext.go b/internal/web3ext/web3ext.go
index 89ebceec7c..3364f41eb7 100644
--- a/internal/web3ext/web3ext.go
+++ b/internal/web3ext/web3ext.go
@@ -21,6 +21,7 @@ var Modules = map[string]string{
 	"admin":      Admin_JS,
 	"chequebook": Chequebook_JS,
 	"clique":     Clique_JS,
+	"ethash":     Ethash_JS,
 	"debug":      Debug_JS,
 	"eth":        Eth_JS,
 	"miner":      Miner_JS,
@@ -109,6 +110,29 @@ web3._extend({
 });
 `
 
+const Ethash_JS = `
+web3._extend({
+	property: 'ethash',
+	methods: [
+		new web3._extend.Method({
+			name: 'getWork',
+			call: 'ethash_getWork',
+			params: 0
+		}),
+		new web3._extend.Method({
+			name: 'submitWork',
+			call: 'ethash_submitWork',
+			params: 3,
+		}),
+		new web3._extend.Method({
+			name: 'submitHashRate',
+			call: 'ethash_submitHashRate',
+			params: 2,
+		}),
+	]
+});
+`
+
 const Admin_JS = `
 web3._extend({
 	property: 'admin',
diff --git a/les/backend.go b/les/backend.go
index 35f67f29f8..952d92cc2a 100644
--- a/les/backend.go
+++ b/les/backend.go
@@ -248,6 +248,7 @@ func (s *LightEthereum) Stop() error {
 	s.blockchain.Stop()
 	s.protocolManager.Stop()
 	s.txPool.Stop()
+	s.engine.Close()
 
 	s.eventMux.Stop()
 
diff --git a/miner/worker.go b/miner/worker.go
index 624be1d0e6..210d22d7e9 100644
--- a/miner/worker.go
+++ b/miner/worker.go
@@ -447,13 +447,6 @@ func (self *worker) commitNewWork() {
 	if self.config.DAOForkSupport && self.config.DAOForkBlock != nil && self.config.DAOForkBlock.Cmp(header.Number) == 0 {
 		misc.ApplyDAOHardFork(work.state)
 	}
-	pending, err := self.eth.TxPool().Pending()
-	if err != nil {
-		log.Error("Failed to fetch pending transactions", "err", err)
-		return
-	}
-	txs := types.NewTransactionsByPriceAndNonce(self.current.signer, pending)
-	work.commitTransactions(self.mux, txs, self.chain, self.coinbase)
 
 	// compute uncles for the new block.
 	var (
@@ -477,16 +470,41 @@ func (self *worker) commitNewWork() {
 	for _, hash := range badUncles {
 		delete(self.possibleUncles, hash)
 	}
-	// Create the new block to seal with the consensus engine
+
+	// Create an empty block based on temporary copied state for sealing in advance without waiting block
+	// execution finished.
+	if work.Block, err = self.engine.Finalize(self.chain, header, work.state.Copy(), 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 atomic.LoadInt32(&self.mining) == 1 {
+			log.Info("Commit new empty mining work", "number", work.Block.Number(), "uncles", len(uncles))
+		}
+		self.push(work)
+	}
+
+	// Fill the block with all available pending transactions.
+	pending, err := self.eth.TxPool().Pending()
+	if err != nil {
+		log.Error("Failed to fetch pending transactions", "err", err)
+		return
+	}
+	txs := types.NewTransactionsByPriceAndNonce(self.current.signer, pending)
+	work.commitTransactions(self.mux, txs, self.chain, self.coinbase)
+
+	// Create the full block to seal with the consensus engine
 	if work.Block, err = self.engine.Finalize(self.chain, header, work.state, work.txs, uncles, work.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 atomic.LoadInt32(&self.mining) == 1 {
-		log.Info("Commit new mining work", "number", work.Block.Number(), "txs", work.tcount, "uncles", len(uncles), "elapsed", common.PrettyDuration(time.Since(tstart)))
+		log.Info("Commit new full mining work", "number", work.Block.Number(), "txs", work.tcount, "uncles", len(uncles), "elapsed", common.PrettyDuration(time.Since(tstart)))
 		self.unconfirmed.Shift(work.Block.NumberU64() - 1)
 	}
+	// Push full work to sealer, which will replace the empty work sent before automatically.
 	self.push(work)
 	self.updateSnapshot()
 }