consensus/ethash: move remote agent logic to ethash internal (#15853)

* consensus/ethash: start remote ggoroutine to handle remote mining

* consensus/ethash: expose remote miner api

* consensus/ethash: expose submitHashrate api

* miner, ethash: push empty block to sealer without waiting execution

* consensus, internal: add getHashrate API for ethash

* consensus: add three method for consensus interface

* miner: expose consensus engine running status to miner

* eth, miner: specify etherbase when miner created

* miner: commit new work when consensus engine is started

* consensus, miner: fix some logics

* all: delete useless interfaces

* consensus: polish a bit

16 files changed, 608 insertions, 361 deletions

diff --git a/cmd/geth/consolecmd_test.go b/cmd/geth/consolecmd_test.go
index 8d8b10f8f..34ba87702 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 8968f500f..59bb3d40b 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. It's a noop for clique as there is are no background threads.
+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 5774af1a7..827175444 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 terminates any background threads maintained by 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 f0c6465fd..e7625f7c0 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
new file mode 100644
index 000000000..a04ea235d
--- /dev/null
+++ b/consensus/ethash/api.go
@@ -0,0 +1,117 @@
+// 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 ethash
+
+import (
+	"errors"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/core/types"
+)
+
+var errEthashStopped = errors.New("ethash stopped")
+
+// API exposes ethash related methods for the RPC interface.
+type API struct {
+	ethash *Ethash // Make sure the mode of ethash is normal.
+}
+
+// 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) {
+	if api.ethash.config.PowMode != ModeNormal && api.ethash.config.PowMode != ModeTest {
+		return [3]string{}, errors.New("not supported")
+	}
+
+	var (
+		workCh = make(chan [3]string, 1)
+		errc   = make(chan error, 1)
+	)
+
+	select {
+	case api.ethash.fetchWorkCh <- &sealWork{errc: errc, res: workCh}:
+	case <-api.ethash.exitCh:
+		return [3]string{}, errEthashStopped
+	}
+
+	select {
+	case work := <-workCh:
+		return work, nil
+	case err := <-errc:
+		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 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 {
+	if api.ethash.config.PowMode != ModeNormal && api.ethash.config.PowMode != ModeTest {
+		return false
+	}
+
+	var errc = make(chan error, 1)
+
+	select {
+	case api.ethash.submitWorkCh <- &mineResult{
+		nonce:     nonce,
+		mixDigest: digest,
+		hash:      hash,
+		errc:      errc,
+	}:
+	case <-api.ethash.exitCh:
+		return false
+	}
+
+	err := <-errc
+	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 (api *API) SubmitHashRate(rate hexutil.Uint64, id common.Hash) bool {
+	if api.ethash.config.PowMode != ModeNormal && api.ethash.config.PowMode != ModeTest {
+		return false
+	}
+
+	var done = make(chan struct{}, 1)
+
+	select {
+	case api.ethash.submitRateCh <- &hashrate{done: done, rate: uint64(rate), id: id}:
+	case <-api.ethash.exitCh:
+		return false
+	}
+
+	// Block until hash rate submitted successfully.
+	<-done
+
+	return true
+}
+
+// GetHashrate returns the current hashrate for local CPU miner and remote miner.
+func (api *API) GetHashrate() uint64 {
+	return uint64(api.ethash.Hashrate())
+}
diff --git a/consensus/ethash/ethash.go b/consensus/ethash/ethash.go
index f79dd6c36..0cb3059b9 100644
--- a/consensus/ethash/ethash.go
+++ b/consensus/ethash/ethash.go
@@ -33,7 +33,9 @@ import (
 	"unsafe"
 
 	mmap "github.com/edsrzf/mmap-go"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/consensus"
+	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -389,6 +391,30 @@ type Config struct {
 	PowMode        Mode
 }
 
+// mineResult wraps the pow solution parameters for the specified block.
+type mineResult struct {
+	nonce     types.BlockNonce
+	mixDigest common.Hash
+	hash      common.Hash
+
+	errc 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{}
+}
+
+// sealWork wraps a seal work package for remote sealer.
+type sealWork struct {
+	errc chan error
+	res  chan [3]string
+}
+
 // Ethash is a consensus engine based on proof-of-work implementing the ethash
 // algorithm.
 type Ethash struct {
@@ -403,15 +429,25 @@ type Ethash struct {
 	update   chan struct{} // Notification channel to update mining parameters
 	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
+	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.
+// New creates a full sized ethash PoW scheme and starts a background thread for remote mining.
 func New(config Config) *Ethash {
 	if config.CachesInMem <= 0 {
 		log.Warn("One ethash cache must always be in memory", "requested", config.CachesInMem)
@@ -423,19 +459,43 @@ func New(config Config) *Ethash {
 	if config.DatasetDir != "" && config.DatasetsOnDisk > 0 {
 		log.Info("Disk storage enabled for ethash DAGs", "dir", config.DatasetDir, "count", config.DatasetsOnDisk)
 	}
-	return &Ethash{
-		config:   config,
-		caches:   newlru("cache", config.CachesInMem, newCache),
-		datasets: newlru("dataset", config.DatasetsInMem, newDataset),
-		update:   make(chan struct{}),
-		hashrate: metrics.NewMeter(),
+	ethash := &Ethash{
+		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()
+	return ethash
 }
 
 // NewTester creates a small sized ethash PoW scheme useful only for testing
 // purposes.
 func NewTester() *Ethash {
-	return New(Config{CachesInMem: 1, PowMode: ModeTest})
+	ethash := &Ethash{
+		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()
+	return ethash
 }
 
 // NewFaker creates a ethash consensus engine with a fake PoW scheme that accepts
@@ -489,6 +549,22 @@ func NewShared() *Ethash {
 	return &Ethash{shared: sharedEthash}
 }
 
+// Close closes the exit channel to notify all backend threads exiting.
+func (ethash *Ethash) Close() error {
+	var err error
+	ethash.closeOnce.Do(func() {
+		// Short circuit if the exit channel is not allocated.
+		if ethash.exitCh == nil {
+			return
+		}
+		errc := make(chan error)
+		ethash.exitCh <- errc
+		err = <-errc
+		close(ethash.exitCh)
+	})
+	return err
+}
+
 // cache tries to retrieve a verification cache for the specified block number
 // by first checking against a list of in-memory caches, then against caches
 // stored on disk, and finally generating one if none can be found.
@@ -561,14 +637,44 @@ func (ethash *Ethash) SetThreads(threads int) {
 
 // Hashrate implements PoW, returning the measured rate of the search invocations
 // per second over the last minute.
+// Note the returned hashrate includes local hashrate, but also includes the total
+// hashrate of all remote miner.
 func (ethash *Ethash) Hashrate() float64 {
-	return ethash.hashrate.Rate1()
+	// Short circuit if we are run the ethash in normal/test mode.
+	if ethash.config.PowMode != ModeNormal && ethash.config.PowMode != ModeTest {
+		return ethash.hashrate.Rate1()
+	}
+	var res = make(chan uint64, 1)
+
+	select {
+	case ethash.fetchRateCh <- res:
+	case <-ethash.exitCh:
+		// Return local hashrate only if ethash is stopped.
+		return ethash.hashrate.Rate1()
+	}
+
+	// Gather total submitted hash rate of remote sealers.
+	return ethash.hashrate.Rate1() + float64(<-res)
 }
 
-// APIs implements consensus.Engine, returning the user facing RPC APIs. Currently
-// that is empty.
+// APIs implements consensus.Engine, returning the user facing RPC APIs.
 func (ethash *Ethash) APIs(chain consensus.ChainReader) []rpc.API {
-	return nil
+	// 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 31116da43..ccdd30fb0 100644
--- a/consensus/ethash/ethash_test.go
+++ b/consensus/ethash/ethash_test.go
@@ -23,7 +23,10 @@ import (
 	"os"
 	"sync"
 	"testing"
+	"time"
 
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/types"
 )
 
@@ -32,6 +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)
@@ -52,6 +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
@@ -77,3 +82,90 @@ func verifyTest(wg *sync.WaitGroup, e *Ethash, workerIndex, epochs int) {
 		e.VerifySeal(nil, head)
 	}
 }
+
+func TestRemoteSealer(t *testing.T) {
+	ethash := NewTester()
+	defer ethash.Close()
+	api := &API{ethash}
+	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.
+	ethash.Seal(nil, block, nil)
+
+	var (
+		work [3]string
+		err  error
+	)
+	if work, err = api.GetWork(); err != nil || work[0] != block.HashNoNonce().Hex() {
+		t.Error("expect to return a mining work has same hash")
+	}
+
+	if res := api.SubmitWork(types.BlockNonce{}, block.HashNoNonce(), common.Hash{}); res {
+		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")
+	}
+}
+
+func TestHashRate(t *testing.T) {
+	var (
+		ethash   = NewTester()
+		api      = &API{ethash}
+		hashrate = []hexutil.Uint64{100, 200, 300}
+		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")
+		}
+		expect += uint64(hashrate[i])
+	}
+	if tot := ethash.Hashrate(); tot != float64(expect) {
+		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 b5e742d8b..a9449d406 100644
--- a/consensus/ethash/sealer.go
+++ b/consensus/ethash/sealer.go
@@ -18,11 +18,13 @@ package ethash
 
 import (
 	crand "crypto/rand"
+	"errors"
 	"math"
 	"math/big"
 	"math/rand"
 	"runtime"
 	"sync"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/consensus"
@@ -30,6 +32,11 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 )
 
+var (
+	errNoMiningWork      = errors.New("no mining work available yet")
+	errInvalidSealResult = errors.New("invalid or stale proof-of-work solution")
+)
+
 // Seal implements consensus.Engine, attempting to find a nonce that satisfies
 // the block's difficulty requirements.
 func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop <-chan struct{}) (*types.Block, error) {
@@ -45,7 +52,6 @@ func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop
 	}
 	// Create a runner and the multiple search threads it directs
 	abort := make(chan struct{})
-	found := make(chan *types.Block)
 
 	ethash.lock.Lock()
 	threads := ethash.threads
@@ -64,12 +70,16 @@ 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
+	if ethash.workCh != nil {
+		ethash.workCh <- block
+	}
 	var pend sync.WaitGroup
 	for i := 0; i < threads; i++ {
 		pend.Add(1)
 		go func(id int, nonce uint64) {
 			defer pend.Done()
-			ethash.mine(block, id, nonce, abort, found)
+			ethash.mine(block, id, nonce, abort, ethash.resultCh)
 		}(i, uint64(ethash.rand.Int63()))
 	}
 	// Wait until sealing is terminated or a nonce is found
@@ -78,7 +88,7 @@ func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop
 	case <-stop:
 		// Outside abort, stop all miner threads
 		close(abort)
-	case result = <-found:
+	case result = <-ethash.resultCh:
 		// One of the threads found a block, abort all others
 		close(abort)
 	case <-ethash.update:
@@ -150,3 +160,136 @@ search:
 	// during sealing so it's not unmapped while being read.
 	runtime.KeepAlive(dataset)
 }
+
+// remote starts a standalone goroutine to handle remote mining related stuff.
+func (ethash *Ethash) remote() {
+	var (
+		works       = make(map[common.Hash]*types.Block)
+		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 := func() ([3]string, error) {
+		var res [3]string
+		if currentWork == nil {
+			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.
+		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 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[hash]
+		if block == nil {
+			log.Info("Work submitted but none pending", "hash", hash)
+			return false
+		}
+
+		// Verify the correctness of submitted result.
+		header := block.Header()
+		header.Nonce = nonce
+		header.MixDigest = mixDigest
+		if err := ethash.VerifySeal(nil, header); err != nil {
+			log.Warn("Invalid proof-of-work submitted", "hash", hash, "err", err)
+			return false
+		}
+
+		// 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 ethash.resultCh <- block.WithSeal(header):
+			delete(works, hash)
+			return true
+		default:
+			log.Info("Work submitted is stale", "hash", hash)
+			return false
+		}
+	}
+
+	ticker := time.NewTicker(5 * time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case block := <-ethash.workCh:
+			if currentWork != nil && block.ParentHash() != currentWork.ParentHash() {
+				// Start new round mining, throw out all previous work.
+				works = make(map[common.Hash]*types.Block)
+			}
+			// Update current work with new received block.
+			// Note same work can be past twice, happens when changing CPU threads.
+			currentWork = block
+
+		case work := <-ethash.fetchWorkCh:
+			// Return current mining work to remote miner.
+			miningWork, err := getWork()
+			if err != nil {
+				work.errc <- err
+			} else {
+				work.res <- miningWork
+			}
+
+		case result := <-ethash.submitWorkCh:
+			// Verify submitted PoW solution based on maintained mining blocks.
+			if submitWork(result.nonce, result.mixDigest, result.hash) {
+				result.errc <- nil
+			} else {
+				result.errc <- 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 submitted hash rate.
+			for id, rate := range rates {
+				if time.Since(rate.ping) > 10*time.Second {
+					delete(rates, id)
+				}
+			}
+
+		case errc := <-ethash.exitCh:
+			// Exit remote loop if ethash is closed and return relevant error.
+			errc <- nil
+			log.Trace("Ethash remote sealer is exiting")
+			return
+		}
+	}
+}
diff --git a/eth/api.go b/eth/api.go
index 0b6da456f..c1fbcb6d4 100644
--- a/eth/api.go
+++ b/eth/api.go
@@ -34,7 +34,6 @@ import (
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/internal/ethapi"
 	"github.com/ethereum/go-ethereum/log"
-	"github.com/ethereum/go-ethereum/miner"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -70,16 +69,12 @@ func (api *PublicEthereumAPI) Hashrate() hexutil.Uint64 {
 // PublicMinerAPI provides an API to control the miner.
 // It offers only methods that operate on data that pose no security risk when it is publicly accessible.
 type PublicMinerAPI struct {
-	e     *Ethereum
-	agent *miner.RemoteAgent
+	e *Ethereum
 }
 
 // NewPublicMinerAPI create a new PublicMinerAPI instance.
 func NewPublicMinerAPI(e *Ethereum) *PublicMinerAPI {
-	agent := miner.NewRemoteAgent(e.BlockChain(), e.Engine())
-	e.Miner().Register(agent)
-
-	return &PublicMinerAPI{e, agent}
+	return &PublicMinerAPI{e}
 }
 
 // Mining returns an indication if this node is currently mining.
@@ -87,37 +82,6 @@ func (api *PublicMinerAPI) Mining() bool {
 	return api.e.IsMining()
 }
 
-// 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 (api *PublicMinerAPI) SubmitWork(nonce types.BlockNonce, solution, digest common.Hash) bool {
-	return api.agent.SubmitWork(nonce, digest, solution)
-}
-
-// 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 *PublicMinerAPI) GetWork() ([3]string, error) {
-	if !api.e.IsMining() {
-		if err := api.e.StartMining(false); err != nil {
-			return [3]string{}, err
-		}
-	}
-	work, err := api.agent.GetWork()
-	if err != nil {
-		return work, fmt.Errorf("mining not ready: %v", err)
-	}
-	return work, 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 (api *PublicMinerAPI) SubmitHashrate(hashrate hexutil.Uint64, id common.Hash) bool {
-	api.agent.SubmitHashrate(id, uint64(hashrate))
-	return true
-}
-
 // PrivateMinerAPI provides private RPC methods to control the miner.
 // These methods can be abused by external users and must be considered insecure for use by untrusted users.
 type PrivateMinerAPI struct {
@@ -132,7 +96,8 @@ func NewPrivateMinerAPI(e *Ethereum) *PrivateMinerAPI {
 // Start the miner with the given number of threads. If threads is nil the number
 // of workers started is equal to the number of logical CPUs that are usable by
 // this process. If mining is already running, this method adjust the number of
-// threads allowed to use.
+// threads allowed to use and updates the minimum price required by the transaction
+// pool.
 func (api *PrivateMinerAPI) Start(threads *int) error {
 	// Set the number of threads if the seal engine supports it
 	if threads == nil {
@@ -153,7 +118,6 @@ func (api *PrivateMinerAPI) Start(threads *int) error {
 		api.e.lock.RLock()
 		price := api.e.gasPrice
 		api.e.lock.RUnlock()
-
 		api.e.txPool.SetGasPrice(price)
 		return api.e.StartMining(true)
 	}
@@ -198,7 +162,7 @@ func (api *PrivateMinerAPI) SetEtherbase(etherbase common.Address) bool {
 
 // GetHashrate returns the current hashrate of the miner.
 func (api *PrivateMinerAPI) GetHashrate() uint64 {
-	return uint64(api.e.miner.HashRate())
+	return api.e.miner.HashRate()
 }
 
 // PrivateAdminAPI is the collection of Ethereum full node-related APIs
diff --git a/eth/backend.go b/eth/backend.go
index a18abdfb5..32946a0ab 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -166,6 +166,7 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 	if eth.protocolManager, err = NewProtocolManager(eth.chainConfig, config.SyncMode, config.NetworkId, eth.eventMux, eth.txPool, eth.engine, eth.blockchain, chainDb); err != nil {
 		return nil, err
 	}
+
 	eth.miner = miner.New(eth, eth.chainConfig, eth.EventMux(), eth.engine)
 	eth.miner.SetExtra(makeExtraData(config.ExtraData))
 
@@ -411,6 +412,7 @@ 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 +423,5 @@ 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 89ebceec7..c2e0cd3f5 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 +110,34 @@ 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: 'getHashrate',
+			call: 'ethash_getHashrate',
+			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 35f67f29f..952d92cc2 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/agent.go b/miner/agent.go
index e3cebbd2e..95d835bd7 100644
--- a/miner/agent.go
+++ b/miner/agent.go
@@ -18,7 +18,6 @@ package miner
 
 import (
 	"sync"
-
 	"sync/atomic"
 
 	"github.com/ethereum/go-ethereum/consensus"
@@ -36,24 +35,31 @@ type CpuAgent struct {
 	chain  consensus.ChainReader
 	engine consensus.Engine
 
-	isMining int32 // isMining indicates whether the agent is currently mining
+	started int32 // started indicates whether the agent is currently started
 }
 
 func NewCpuAgent(chain consensus.ChainReader, engine consensus.Engine) *CpuAgent {
-	miner := &CpuAgent{
+	agent := &CpuAgent{
 		chain:  chain,
 		engine: engine,
 		stop:   make(chan struct{}, 1),
 		workCh: make(chan *Work, 1),
 	}
-	return miner
+	return agent
 }
 
 func (self *CpuAgent) Work() chan<- *Work            { return self.workCh }
 func (self *CpuAgent) SetReturnCh(ch chan<- *Result) { 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.isMining, 1, 0) {
+	if !atomic.CompareAndSwapInt32(&self.started, 1, 0) {
 		return // agent already stopped
 	}
 	self.stop <- struct{}{}
@@ -68,13 +74,6 @@ done:
 	}
 }
 
-func (self *CpuAgent) Start() {
-	if !atomic.CompareAndSwapInt32(&self.isMining, 0, 1) {
-		return // agent already started
-	}
-	go self.update()
-}
-
 func (self *CpuAgent) update() {
 out:
 	for {
@@ -110,10 +109,3 @@ func (self *CpuAgent) mine(work *Work, stop <-chan struct{}) {
 		self.returnCh <- nil
 	}
 }
-
-func (self *CpuAgent) GetHashRate() int64 {
-	if pow, ok := self.engine.(consensus.PoW); ok {
-		return int64(pow.Hashrate())
-	}
-	return 0
-}
diff --git a/miner/miner.go b/miner/miner.go
index d9256e978..4c5717c8a 100644
--- a/miner/miner.go
+++ b/miner/miner.go
@@ -44,12 +44,9 @@ type Backend interface {
 
 // Miner creates blocks and searches for proof-of-work values.
 type Miner struct {
-	mux *event.TypeMux
-
-	worker *worker
-
+	mux      *event.TypeMux
+	worker   *worker
 	coinbase common.Address
-	mining   int32
 	eth      Backend
 	engine   consensus.Engine
 
@@ -62,7 +59,7 @@ func New(eth Backend, config *params.ChainConfig, mux *event.TypeMux, engine con
 		eth:      eth,
 		mux:      mux,
 		engine:   engine,
-		worker:   newWorker(config, engine, common.Address{}, eth, mux),
+		worker:   newWorker(config, engine, eth, mux),
 		canStart: 1,
 	}
 	miner.Register(NewCpuAgent(eth.BlockChain(), engine))
@@ -111,23 +108,16 @@ func (self *Miner) Start(coinbase common.Address) {
 		log.Info("Network syncing, will start miner afterwards")
 		return
 	}
-	atomic.StoreInt32(&self.mining, 1)
-
-	log.Info("Starting mining operation")
 	self.worker.start()
 	self.worker.commitNewWork()
 }
 
 func (self *Miner) Stop() {
 	self.worker.stop()
-	atomic.StoreInt32(&self.mining, 0)
 	atomic.StoreInt32(&self.shouldStart, 0)
 }
 
 func (self *Miner) Register(agent Agent) {
-	if self.Mining() {
-		agent.Start()
-	}
 	self.worker.register(agent)
 }
 
@@ -136,22 +126,14 @@ func (self *Miner) Unregister(agent Agent) {
 }
 
 func (self *Miner) Mining() bool {
-	return atomic.LoadInt32(&self.mining) > 0
+	return self.worker.isRunning()
 }
 
-func (self *Miner) HashRate() (tot int64) {
+func (self *Miner) HashRate() uint64 {
 	if pow, ok := self.engine.(consensus.PoW); ok {
-		tot += int64(pow.Hashrate())
-	}
-	// do we care this might race? is it worth we're rewriting some
-	// aspects of the worker/locking up agents so we can get an accurate
-	// hashrate?
-	for agent := range self.worker.agents {
-		if _, ok := agent.(*CpuAgent); !ok {
-			tot += agent.GetHashRate()
-		}
+		return uint64(pow.Hashrate())
 	}
-	return
+	return 0
 }
 
 func (self *Miner) SetExtra(extra []byte) error {
diff --git a/miner/remote_agent.go b/miner/remote_agent.go
deleted file mode 100644
index 287e7530c..000000000
--- a/miner/remote_agent.go
+++ /dev/null
@@ -1,202 +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 (
-	"errors"
-	"math/big"
-	"sync"
-	"sync/atomic"
-	"time"
-
-	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/consensus"
-	"github.com/ethereum/go-ethereum/consensus/ethash"
-	"github.com/ethereum/go-ethereum/core/types"
-	"github.com/ethereum/go-ethereum/log"
-)
-
-type hashrate struct {
-	ping time.Time
-	rate uint64
-}
-
-type RemoteAgent struct {
-	mu sync.Mutex
-
-	quitCh   chan struct{}
-	workCh   chan *Work
-	returnCh chan<- *Result
-
-	chain       consensus.ChainReader
-	engine      consensus.Engine
-	currentWork *Work
-	work        map[common.Hash]*Work
-
-	hashrateMu sync.RWMutex
-	hashrate   map[common.Hash]hashrate
-
-	running int32 // running indicates whether the agent is active. Call atomically
-}
-
-func NewRemoteAgent(chain consensus.ChainReader, engine consensus.Engine) *RemoteAgent {
-	return &RemoteAgent{
-		chain:    chain,
-		engine:   engine,
-		work:     make(map[common.Hash]*Work),
-		hashrate: make(map[common.Hash]hashrate),
-	}
-}
-
-func (a *RemoteAgent) SubmitHashrate(id common.Hash, rate uint64) {
-	a.hashrateMu.Lock()
-	defer a.hashrateMu.Unlock()
-
-	a.hashrate[id] = hashrate{time.Now(), rate}
-}
-
-func (a *RemoteAgent) Work() chan<- *Work {
-	return a.workCh
-}
-
-func (a *RemoteAgent) SetReturnCh(returnCh chan<- *Result) {
-	a.returnCh = returnCh
-}
-
-func (a *RemoteAgent) Start() {
-	if !atomic.CompareAndSwapInt32(&a.running, 0, 1) {
-		return
-	}
-	a.quitCh = make(chan struct{})
-	a.workCh = make(chan *Work, 1)
-	go a.loop(a.workCh, a.quitCh)
-}
-
-func (a *RemoteAgent) Stop() {
-	if !atomic.CompareAndSwapInt32(&a.running, 1, 0) {
-		return
-	}
-	close(a.quitCh)
-	close(a.workCh)
-}
-
-// GetHashRate returns the accumulated hashrate of all identifier combined
-func (a *RemoteAgent) GetHashRate() (tot int64) {
-	a.hashrateMu.RLock()
-	defer a.hashrateMu.RUnlock()
-
-	// this could overflow
-	for _, hashrate := range a.hashrate {
-		tot += int64(hashrate.rate)
-	}
-	return
-}
-
-func (a *RemoteAgent) GetWork() ([3]string, error) {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-
-	var res [3]string
-
-	if a.currentWork != nil {
-		block := a.currentWork.Block
-
-		res[0] = block.HashNoNonce().Hex()
-		seedHash := ethash.SeedHash(block.NumberU64())
-		res[1] = common.BytesToHash(seedHash).Hex()
-		// Calculate the "target" to be returned to the external miner
-		n := big.NewInt(1)
-		n.Lsh(n, 255)
-		n.Div(n, block.Difficulty())
-		n.Lsh(n, 1)
-		res[2] = common.BytesToHash(n.Bytes()).Hex()
-
-		a.work[block.HashNoNonce()] = a.currentWork
-		return res, nil
-	}
-	return res, errors.New("No work available yet, don't panic.")
-}
-
-// SubmitWork tries to inject a pow solution into the remote agent, 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).
-func (a *RemoteAgent) SubmitWork(nonce types.BlockNonce, mixDigest, hash common.Hash) bool {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-
-	// Make sure the work submitted is present
-	work := a.work[hash]
-	if work == nil {
-		log.Info("Work submitted but none pending", "hash", hash)
-		return false
-	}
-	// Make sure the Engine solutions is indeed valid
-	result := work.Block.Header()
-	result.Nonce = nonce
-	result.MixDigest = mixDigest
-
-	if err := a.engine.VerifySeal(a.chain, result); err != nil {
-		log.Warn("Invalid proof-of-work submitted", "hash", hash, "err", err)
-		return false
-	}
-	block := work.Block.WithSeal(result)
-
-	// Solutions seems to be valid, return to the miner and notify acceptance
-	a.returnCh <- &Result{work, block}
-	delete(a.work, hash)
-
-	return true
-}
-
-// loop monitors mining events on the work and quit channels, updating the internal
-// state of the remote miner until a termination is requested.
-//
-// Note, the reason the work and quit channels are passed as parameters is because
-// RemoteAgent.Start() constantly recreates these channels, so the loop code cannot
-// assume data stability in these member fields.
-func (a *RemoteAgent) loop(workCh chan *Work, quitCh chan struct{}) {
-	ticker := time.NewTicker(5 * time.Second)
-	defer ticker.Stop()
-
-	for {
-		select {
-		case <-quitCh:
-			return
-		case work := <-workCh:
-			a.mu.Lock()
-			a.currentWork = work
-			a.mu.Unlock()
-		case <-ticker.C:
-			// cleanup
-			a.mu.Lock()
-			for hash, work := range a.work {
-				if time.Since(work.createdAt) > 7*(12*time.Second) {
-					delete(a.work, hash)
-				}
-			}
-			a.mu.Unlock()
-
-			a.hashrateMu.Lock()
-			for id, hashrate := range a.hashrate {
-				if time.Since(hashrate.ping) > 10*time.Second {
-					delete(a.hashrate, id)
-				}
-			}
-			a.hashrateMu.Unlock()
-		}
-	}
-}
diff --git a/miner/worker.go b/miner/worker.go
index 34329f849..f1194fa18 100644
--- a/miner/worker.go
+++ b/miner/worker.go
@@ -55,9 +55,8 @@ const (
 type Agent interface {
 	Work() chan<- *Work
 	SetReturnCh(chan<- *Result)
-	Stop()
 	Start()
-	GetHashRate() int64
+	Stop()
 }
 
 // Work is the workers current environment and holds
@@ -102,7 +101,6 @@ type worker struct {
 	chainHeadSub event.Subscription
 	chainSideCh  chan core.ChainSideEvent
 	chainSideSub event.Subscription
-	wg           sync.WaitGroup
 
 	agents map[Agent]struct{}
 	recv   chan *Result
@@ -128,11 +126,11 @@ type worker struct {
 	unconfirmed *unconfirmedBlocks // set of locally mined blocks pending canonicalness confirmations
 
 	// atomic status counters
-	mining int32
-	atWork int32
+	atWork  int32 // The number of in-flight consensus engine work.
+	running int32 // The indicator whether the consensus engine is running or not.
 }
 
-func newWorker(config *params.ChainConfig, engine consensus.Engine, coinbase common.Address, eth Backend, mux *event.TypeMux) *worker {
+func newWorker(config *params.ChainConfig, engine consensus.Engine, eth Backend, mux *event.TypeMux) *worker {
 	worker := &worker{
 		config:         config,
 		engine:         engine,
@@ -146,7 +144,6 @@ func newWorker(config *params.ChainConfig, engine consensus.Engine, coinbase com
 		chain:          eth.BlockChain(),
 		proc:           eth.BlockChain().Validator(),
 		possibleUncles: make(map[common.Hash]*types.Block),
-		coinbase:       coinbase,
 		agents:         make(map[Agent]struct{}),
 		unconfirmed:    newUnconfirmedBlocks(eth.BlockChain(), miningLogAtDepth),
 	}
@@ -176,62 +173,51 @@ func (self *worker) setExtra(extra []byte) {
 }
 
 func (self *worker) pending() (*types.Block, *state.StateDB) {
-	if atomic.LoadInt32(&self.mining) == 0 {
-		// return a snapshot to avoid contention on currentMu mutex
-		self.snapshotMu.RLock()
-		defer self.snapshotMu.RUnlock()
-		return self.snapshotBlock, self.snapshotState.Copy()
-	}
-
-	self.currentMu.Lock()
-	defer self.currentMu.Unlock()
-	return self.current.Block, self.current.state.Copy()
+	// return a snapshot to avoid contention on currentMu mutex
+	self.snapshotMu.RLock()
+	defer self.snapshotMu.RUnlock()
+	return self.snapshotBlock, self.snapshotState.Copy()
 }
 
 func (self *worker) pendingBlock() *types.Block {
-	if atomic.LoadInt32(&self.mining) == 0 {
-		// return a snapshot to avoid contention on currentMu mutex
-		self.snapshotMu.RLock()
-		defer self.snapshotMu.RUnlock()
-		return self.snapshotBlock
-	}
-
-	self.currentMu.Lock()
-	defer self.currentMu.Unlock()
-	return self.current.Block
+	// return a snapshot to avoid contention on currentMu mutex
+	self.snapshotMu.RLock()
+	defer self.snapshotMu.RUnlock()
+	return self.snapshotBlock
 }
 
 func (self *worker) start() {
 	self.mu.Lock()
 	defer self.mu.Unlock()
-
-	atomic.StoreInt32(&self.mining, 1)
-
-	// spin up agents
+	atomic.StoreInt32(&self.running, 1)
 	for agent := range self.agents {
 		agent.Start()
 	}
 }
 
 func (self *worker) stop() {
-	self.wg.Wait()
-
 	self.mu.Lock()
 	defer self.mu.Unlock()
-	if atomic.LoadInt32(&self.mining) == 1 {
-		for agent := range self.agents {
-			agent.Stop()
-		}
+
+	atomic.StoreInt32(&self.running, 0)
+	for agent := range self.agents {
+		agent.Stop()
 	}
-	atomic.StoreInt32(&self.mining, 0)
 	atomic.StoreInt32(&self.atWork, 0)
 }
 
+func (self *worker) isRunning() bool {
+	return atomic.LoadInt32(&self.running) == 1
+}
+
 func (self *worker) register(agent Agent) {
 	self.mu.Lock()
 	defer self.mu.Unlock()
 	self.agents[agent] = struct{}{}
 	agent.SetReturnCh(self.recv)
+	if self.isRunning() {
+		agent.Start()
+	}
 }
 
 func (self *worker) unregister(agent Agent) {
@@ -266,7 +252,7 @@ func (self *worker) update() {
 			// Note all transactions received may not be continuous with transactions
 			// already included in the current mining block. These transactions will
 			// be automatically eliminated.
-			if atomic.LoadInt32(&self.mining) == 0 {
+			if !self.isRunning() {
 				self.currentMu.Lock()
 				txs := make(map[common.Address]types.Transactions)
 				for _, tx := range ev.Txs {
@@ -343,9 +329,6 @@ func (self *worker) wait() {
 
 // push sends a new work task to currently live miner agents.
 func (self *worker) push(work *Work) {
-	if atomic.LoadInt32(&self.mining) != 1 {
-		return
-	}
 	for agent := range self.agents {
 		atomic.AddInt32(&self.atWork, 1)
 		if ch := agent.Work(); ch != nil {
@@ -416,8 +399,12 @@ func (self *worker) commitNewWork() {
 		Extra:      self.extra,
 		Time:       big.NewInt(tstamp),
 	}
-	// Only set the coinbase if we are mining (avoid spurious block rewards)
-	if atomic.LoadInt32(&self.mining) == 1 {
+	// Only set the coinbase if our consensus engine is running (avoid spurious block rewards)
+	if self.isRunning() {
+		if self.coinbase == (common.Address{}) {
+			log.Error("Refusing to mine without etherbase")
+			return
+		}
 		header.Coinbase = self.coinbase
 	}
 	if err := self.engine.Prepare(self.chain, header); err != nil {
@@ -448,13 +435,6 @@ 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 (
@@ -478,17 +458,41 @@ 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 self.isRunning() {
+			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)))
+	if self.isRunning() {
+		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)
+		self.push(work)
 	}
-	self.push(work)
 	self.updateSnapshot()
 }
 
@@ -511,10 +515,19 @@ 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,
-		nil,
+		uncles,
 		self.current.receipts,
 	)
 	self.snapshotState = self.current.state.Copy()