eth, xeth: fix GasPriceOracle goroutine leak

XEth.gpo was being initialized as needed. WithState copies the XEth
struct including the gpo field. If gpo was nil at the time of the copy
and Call or Transact were invoked on it, an additional GPO listenLoop
would be spawned.

Move the lazy initialization to GasPriceOracle instead so the same GPO
instance is shared among all created XEths.

Fixes #1317
Might help with #1930

eth/gasprice.go

@@ -23,49 +23,66 @@ import (
 
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
-	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/logger"
 	"github.com/ethereum/go-ethereum/logger/glog"
 )
 
-const gpoProcessPastBlocks = 100
+const (
+	gpoProcessPastBlocks = 100
+
+	// for testing
+	gpoDefaultBaseCorrectionFactor = 110
+	gpoDefaultMinGasPrice          = 10000000000000
+)
 
 type blockPriceInfo struct {
 	baseGasPrice *big.Int
 }
 
+// GasPriceOracle recommends gas prices based on the content of recent
+// blocks.
 type GasPriceOracle struct {
-	eth                           *Ethereum
-	chain                         *core.BlockChain
-	events                        event.Subscription
+	eth           *Ethereum
+	initOnce      sync.Once
+	minPrice      *big.Int
+	lastBaseMutex sync.Mutex
+	lastBase      *big.Int
+
+	// state of listenLoop
 	blocks                        map[uint64]*blockPriceInfo
 	firstProcessed, lastProcessed uint64
-	lastBaseMutex                 sync.Mutex
-	lastBase, minBase             *big.Int
+	minBase                       *big.Int
+}
+
+// NewGasPriceOracle returns a new oracle.
+func NewGasPriceOracle(eth *Ethereum) *GasPriceOracle {
+	minprice := eth.GpoMinGasPrice
+	if minprice == nil {
+		minprice = big.NewInt(gpoDefaultMinGasPrice)
+	}
+	minbase := new(big.Int).Mul(minprice, big.NewInt(100))
+	if eth.GpobaseCorrectionFactor > 0 {
+		minbase = minbase.Div(minbase, big.NewInt(int64(eth.GpobaseCorrectionFactor)))
+	}
+	return &GasPriceOracle{
+		eth:      eth,
+		blocks:   make(map[uint64]*blockPriceInfo),
+		minBase:  minbase,
+		minPrice: minprice,
+		lastBase: minprice,
+	}
 }
 
-func NewGasPriceOracle(eth *Ethereum) (self *GasPriceOracle) {
-	self = &GasPriceOracle{}
-	self.blocks = make(map[uint64]*blockPriceInfo)
-	self.eth = eth
-	self.chain = eth.blockchain
-	self.events = eth.EventMux().Subscribe(
-		core.ChainEvent{},
-		core.ChainSplitEvent{},
-	)
-
-	minbase := new(big.Int).Mul(self.eth.GpoMinGasPrice, big.NewInt(100))
-	minbase = minbase.Div(minbase, big.NewInt(int64(self.eth.GpobaseCorrectionFactor)))
-	self.minBase = minbase
-
-	self.processPastBlocks()
-	go self.listenLoop()
-	return
+func (gpo *GasPriceOracle) init() {
+	gpo.initOnce.Do(func() {
+		gpo.processPastBlocks(gpo.eth.BlockChain())
+		go gpo.listenLoop()
+	})
 }
 
-func (self *GasPriceOracle) processPastBlocks() {
+func (self *GasPriceOracle) processPastBlocks(chain *core.BlockChain) {
 	last := int64(-1)
-	cblock := self.chain.CurrentBlock()
+	cblock := chain.CurrentBlock()
 	if cblock != nil {
 		last = int64(cblock.NumberU64())
 	}
@@ -75,7 +92,7 @@ func (self *GasPriceOracle) processPastBlocks() {
 	}
 	self.firstProcessed = uint64(first)
 	for i := first; i <= last; i++ {
-		block := self.chain.GetBlockByNumber(uint64(i))
+		block := chain.GetBlockByNumber(uint64(i))
 		if block != nil {
 			self.processBlock(block)
 		}
@@ -84,9 +101,10 @@ func (self *GasPriceOracle) processPastBlocks() {
 }
 
 func (self *GasPriceOracle) listenLoop() {
-	defer self.events.Unsubscribe()
+	events := self.eth.EventMux().Subscribe(core.ChainEvent{}, core.ChainSplitEvent{})
+	defer events.Unsubscribe()
 
-	for event := range self.events.Chan() {
+	for event := range events.Chan() {
 		switch event := event.Data.(type) {
 		case core.ChainEvent:
 			self.processBlock(event.Block)
@@ -102,7 +120,7 @@ func (self *GasPriceOracle) processBlock(block *types.Block) {
 		self.lastProcessed = i
 	}
 
-	lastBase := self.eth.GpoMinGasPrice
+	lastBase := self.minPrice
 	bpl := self.blocks[i-1]
 	if bpl != nil {
 		lastBase = bpl.baseGasPrice
@@ -176,28 +194,19 @@ func (self *GasPriceOracle) lowestPrice(block *types.Block) *big.Int {
 	return minPrice
 }
 
+// SuggestPrice returns the recommended gas price.
 func (self *GasPriceOracle) SuggestPrice() *big.Int {
+	self.init()
 	self.lastBaseMutex.Lock()
-	base := self.lastBase
+	price := new(big.Int).Set(self.lastBase)
 	self.lastBaseMutex.Unlock()
 
-	if base == nil {
-		base = self.eth.GpoMinGasPrice
+	price.Mul(price, big.NewInt(int64(self.eth.GpobaseCorrectionFactor)))
+	price.Div(price, big.NewInt(100))
+	if price.Cmp(self.minPrice) < 0 {
+		price.Set(self.minPrice)
+	} else if self.eth.GpoMaxGasPrice != nil && price.Cmp(self.eth.GpoMaxGasPrice) > 0 {
+		price.Set(self.eth.GpoMaxGasPrice)
 	}
-	if base == nil {
-		return big.NewInt(10000000000000) // apparently MinGasPrice is not initialized during some tests
-	}
-
-	baseCorr := new(big.Int).Mul(base, big.NewInt(int64(self.eth.GpobaseCorrectionFactor)))
-	baseCorr.Div(baseCorr, big.NewInt(100))
-
-	if baseCorr.Cmp(self.eth.GpoMinGasPrice) < 0 {
-		return self.eth.GpoMinGasPrice
-	}
-
-	if baseCorr.Cmp(self.eth.GpoMaxGasPrice) > 0 {
-		return self.eth.GpoMaxGasPrice
-	}
-
-	return baseCorr
+	return price
 }

xeth/xeth.go

@@ -59,24 +59,8 @@ const (
 	LogFilterTy
 )
 
-func DefaultGas() *big.Int { return new(big.Int).Set(defaultGas) }
-
-func (self *XEth) DefaultGasPrice() *big.Int {
-	if self.gpo == nil {
-		self.gpo = eth.NewGasPriceOracle(self.backend)
-	}
-	return self.gpo.SuggestPrice()
-}
-
 type XEth struct {
-	backend  *eth.Ethereum
-	frontend Frontend
-
-	state   *State
-	whisper *Whisper
-
-	quit          chan struct{}
-	filterManager *filters.FilterSystem
+	quit chan struct{}
 
 	logMu    sync.RWMutex
 	logQueue map[int]*logQueue
@@ -92,16 +76,18 @@ type XEth struct {
 
 	transactMu sync.Mutex
 
-	agent *miner.RemoteAgent
-
-	gpo *eth.GasPriceOracle
+	// read-only fields
+	backend       *eth.Ethereum
+	frontend      Frontend
+	agent         *miner.RemoteAgent
+	gpo           *eth.GasPriceOracle
+	state         *State
+	whisper       *Whisper
+	filterManager *filters.FilterSystem
 }
 
 func NewTest(eth *eth.Ethereum, frontend Frontend) *XEth {
-	return &XEth{
-		backend:  eth,
-		frontend: frontend,
-	}
+	return &XEth{backend: eth, frontend: frontend}
 }
 
 // New creates an XEth that uses the given frontend.
@@ -118,6 +104,7 @@ func New(ethereum *eth.Ethereum, frontend Frontend) *XEth {
 		transactionQueue: make(map[int]*hashQueue),
 		messages:         make(map[int]*whisperFilter),
 		agent:            miner.NewRemoteAgent(),
+		gpo:              eth.NewGasPriceOracle(ethereum),
 	}
 	if ethereum.Whisper() != nil {
 		xeth.whisper = NewWhisper(ethereum.Whisper())
@@ -207,6 +194,12 @@ func cTopics(t [][]string) [][]common.Hash {
 	return topics
 }
 
+func DefaultGas() *big.Int { return new(big.Int).Set(defaultGas) }
+
+func (self *XEth) DefaultGasPrice() *big.Int {
+	return self.gpo.SuggestPrice()
+}
+
 func (self *XEth) RemoteMining() *miner.RemoteAgent { return self.agent }
 
 func (self *XEth) AtStateNum(num int64) *XEth {