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// Copyright 2016 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 gasprice
import (
"context"
"math/big"
"sort"
"sync"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/internal/ethapi"
"github.com/ethereum/go-ethereum/rpc"
)
const (
LpoAvgCount = 5
LpoMinCount = 3
LpoMaxBlocks = 20
LpoSelect = 50
LpoDefaultPrice = 20000000000
)
// LightPriceOracle recommends gas prices based on the content of recent
// blocks. Suitable for both light and full clients.
type LightPriceOracle struct {
backend ethapi.Backend
lastHead common.Hash
lastPrice *big.Int
cacheLock sync.RWMutex
fetchLock sync.Mutex
}
// NewLightPriceOracle returns a new oracle.
func NewLightPriceOracle(backend ethapi.Backend) *LightPriceOracle {
return &LightPriceOracle{
backend: backend,
lastPrice: big.NewInt(LpoDefaultPrice),
}
}
// SuggestPrice returns the recommended gas price.
func (self *LightPriceOracle) SuggestPrice(ctx context.Context) (*big.Int, error) {
self.cacheLock.RLock()
lastHead := self.lastHead
lastPrice := self.lastPrice
self.cacheLock.RUnlock()
head, _ := self.backend.HeaderByNumber(ctx, rpc.LatestBlockNumber)
headHash := head.Hash()
if headHash == lastHead {
return lastPrice, nil
}
self.fetchLock.Lock()
defer self.fetchLock.Unlock()
// try checking the cache again, maybe the last fetch fetched what we need
self.cacheLock.RLock()
lastHead = self.lastHead
lastPrice = self.lastPrice
self.cacheLock.RUnlock()
if headHash == lastHead {
return lastPrice, nil
}
blockNum := head.Number.Uint64()
chn := make(chan lpResult, LpoMaxBlocks)
sent := 0
exp := 0
var lps bigIntArray
for sent < LpoAvgCount && blockNum > 0 {
go self.getLowestPrice(ctx, blockNum, chn)
sent++
exp++
blockNum--
}
maxEmpty := LpoAvgCount - LpoMinCount
for exp > 0 {
res := <-chn
if res.err != nil {
return nil, res.err
}
exp--
if res.price != nil {
lps = append(lps, res.price)
} else {
if maxEmpty > 0 {
maxEmpty--
} else {
if blockNum > 0 && sent < LpoMaxBlocks {
go self.getLowestPrice(ctx, blockNum, chn)
sent++
exp++
blockNum--
}
}
}
}
price := lastPrice
if len(lps) > 0 {
sort.Sort(lps)
price = lps[(len(lps)-1)*LpoSelect/100]
}
self.cacheLock.Lock()
self.lastHead = headHash
self.lastPrice = price
self.cacheLock.Unlock()
return price, nil
}
type lpResult struct {
price *big.Int
err error
}
// getLowestPrice calculates the lowest transaction gas price in a given block
// and sends it to the result channel. If the block is empty, price is nil.
func (self *LightPriceOracle) getLowestPrice(ctx context.Context, blockNum uint64, chn chan lpResult) {
block, err := self.backend.BlockByNumber(ctx, rpc.BlockNumber(blockNum))
if block == nil {
chn <- lpResult{nil, err}
return
}
txs := block.Transactions()
if len(txs) == 0 {
chn <- lpResult{nil, nil}
return
}
// find smallest gasPrice
minPrice := txs[0].GasPrice()
for i := 1; i < len(txs); i++ {
price := txs[i].GasPrice()
if price.Cmp(minPrice) < 0 {
minPrice = price
}
}
chn <- lpResult{minPrice, nil}
}
type bigIntArray []*big.Int
func (s bigIntArray) Len() int { return len(s) }
func (s bigIntArray) Less(i, j int) bool { return s[i].Cmp(s[j]) < 0 }
func (s bigIntArray) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
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