// Copyright 2017 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 implements the ethash proof-of-work consensus engine.
package ethash
import (
"errors"
"fmt"
"math"
"math/big"
"math/rand"
"os"
"path/filepath"
"reflect"
"strconv"
"sync"
"time"
"unsafe"
mmap "github.com/edsrzf/mmap-go"
"github.com/ethereum/go-ethereum/consensus"
"github.com/ethereum/go-ethereum/log"
"github.com/ethereum/go-ethereum/rpc"
metrics "github.com/rcrowley/go-metrics"
)
var ErrInvalidDumpMagic = errors.New("invalid dump magic")
var (
// maxUint256 is a big integer representing 2^256-1
maxUint256 = new(big.Int).Exp(big.NewInt(2), big.NewInt(256), big.NewInt(0))
// sharedEthash is a full instance that can be shared between multiple users.
sharedEthash = New("", 3, 0, "", 1, 0)
// algorithmRevision is the data structure version used for file naming.
algorithmRevision = 23
// dumpMagic is a dataset dump header to sanity check a data dump.
dumpMagic = []uint32{0xbaddcafe, 0xfee1dead}
)
// isLittleEndian returns whether the local system is running in little or big
// endian byte order.
func isLittleEndian() bool {
n := uint32(0x01020304)
return *(*byte)(unsafe.Pointer(&n)) == 0x04
}
// memoryMap tries to memory map a file of uint32s for read only access.
func memoryMap(path string) (*os.File, mmap.MMap, []uint32, error) {
file, err := os.OpenFile(path, os.O_RDONLY, 0644)
if err != nil {
return nil, nil, nil, err
}
mem, buffer, err := memoryMapFile(file, false)
if err != nil {
file.Close()
return nil, nil, nil, err
}
for i, magic := range dumpMagic {
if buffer[i] != magic {
mem.Unmap()
file.Close()
return nil, nil, nil, ErrInvalidDumpMagic
}
}
return file, mem, buffer[len(dumpMagic):], err
}
// memoryMapFile tries to memory map an already opened file descriptor.
func memoryMapFile(file *os.File, write bool) (mmap.MMap, []uint32, error) {
// Try to memory map the file
flag := mmap.RDONLY
if write {
flag = mmap.RDWR
}
mem, err := mmap.Map(file, flag, 0)
if err != nil {
return nil, nil, err
}
// Yay, we managed to memory map the file, here be dragons
header := *(*reflect.SliceHeader)(unsafe.Pointer(&mem))
header.Len /= 4
header.Cap /= 4
return mem, *(*[]uint32)(unsafe.Pointer(&header)), nil
}
// memoryMapAndGenerate tries to memory map a temporary file of uint32s for write
// access, fill it with the data from a generator and then move it into the final
// path requested.
func memoryMapAndGenerate(path string, size uint64, generator func(buffer []uint32)) (*os.File, mmap.MMap, []uint32, error) {
// Ensure the data folder exists
if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
return nil, nil, nil, err
}
// Create a huge temporary empty file to fill with data
temp := path + "." + strconv.Itoa(rand.Int())
dump, err := os.Create(temp)
if err != nil {
return nil, nil, nil, err
}
if err = dump.Truncate(int64(len(dumpMagic))*4 + int64(size)); err != nil {
return nil, nil, nil, err
}
// Memory map the file for writing and fill it with the generator
mem, buffer, err := memoryMapFile(dump, true)
if err != nil {
dump.Close()
return nil, nil, nil, err
}
copy(buffer, dumpMagic)
data := buffer[len(dumpMagic):]
generator(data)
if err := mem.Unmap(); err != nil {
return nil, nil, nil, err
}
if err := dump.Close(); err != nil {
return nil, nil, nil, err
}
if err := os.Rename(temp, path); err != nil {
return nil, nil, nil, err
}
return memoryMap(path)
}
// cache wraps an ethash cache with some metadata to allow easier concurrent use.
type cache struct {
epoch uint64 // Epoch for which this cache is relevant
dump *os.File // File descriptor of the memory mapped cache
mmap mmap.MMap // Memory map itself to unmap before releasing
cache []uint32 // The actual cache data content (may be memory mapped)
used time.Time // Timestamp of the last use for smarter eviction
once sync.Once // Ensures the cache is generated only once
lock sync.Mutex // Ensures thread safety for updating the usage time
}
// generate ensures that the cache content is generated before use.
func (c *cache) generate(dir string, limit int, test bool) {
c.once.Do(func() {
// If we have a testing cache, generate and return
if test {
c.cache = make([]uint32, 1024/4)
generateCache(c.cache, c.epoch, seedHash(c.epoch*epochLength+1))
return
}
// If we don't store anything on disk, generate and return
size := cacheSize(c.epoch*epochLength + 1)
seed := seedHash(c.epoch*epochLength + 1)
if dir == "" {
c.cache = make([]uint32, size/4)
generateCache(c.cache, c.epoch, seed)
return
}
// Disk storage is needed, this will get fancy
var endian string
if !isLittleEndian() {
endian = ".be"
}
path := filepath.Join(dir, fmt.Sprintf("cache-R%d-%x%s", algorithmRevision, seed[:8], endian))
logger := log.New("epoch", c.epoch)
// Try to load the file from disk and memory map it
var err error
c.dump, c.mmap, c.cache, err = memoryMap(path)
if err == nil {
logger.Debug("Loaded old ethash cache from disk")
return
}
logger.Debug("Failed to load old ethash cache", "err", err)
// No previous cache available, create a new cache file to fill
c.dump, c.mmap, c.cache, err = memoryMapAndGenerate(path, size, func(buffer []uint32) { generateCache(buffer, c.epoch, seed) })
if err != nil {
logger.Error("Failed to generate mapped ethash cache", "err", err)
c.cache = make([]uint32, size/4)
generateCache(c.cache, c.epoch, seed)
}
// Iterate over all previous instances and delete old ones
for ep := int(c.epoch) - limit; ep >= 0; ep-- {
seed := seedHash(uint64(ep)*epochLength + 1)
path := filepath.Join(dir, fmt.Sprintf("cache-R%d-%x%s", algorithmRevision, seed[:8], endian))
os.Remove(path)
}
})
}
// release closes any file handlers and memory maps open.
func (c *cache) release() {
if c.mmap != nil {
c.mmap.Unmap()
c.mmap = nil
}
if c.dump != nil {
c.dump.Close()
c.dump = nil
}
}
// dataset wraps an ethash dataset with some metadata to allow easier concurrent use.
type dataset struct {
epoch uint64 // Epoch for which this cache is relevant
dump *os.File // File descriptor of the memory mapped cache
mmap mmap.MMap // Memory map itself to unmap before releasing
dataset []uint32 // The actual cache data content
used time.Time // Timestamp of the last use for smarter eviction
once sync.Once // Ensures the cache is generated only once
lock sync.Mutex // Ensures thread safety for updating the usage time
}
// generate ensures that the dataset content is generated before use.
func (d *dataset) generate(dir string, limit int, test bool) {
d.once.Do(func() {
// If we have a testing dataset, generate and return
if test {
cache := make([]uint32, 1024/4)
generateCache(cache, d.epoch, seedHash(d.epoch*epochLength+1))
d.dataset = make([]uint32, 32*1024/4)
generateDataset(d.dataset, d.epoch, cache)
return
}
// If we don't store anything on disk, generate and return
csize := cacheSize(d.epoch*epochLength + 1)
dsize := datasetSize(d.epoch*epochLength + 1)
seed := seedHash(d.epoch*epochLength + 1)
if dir == "" {
cache := make([]uint32, csize/4)
generateCache(cache, d.epoch, seed)
d.dataset = make([]uint32, dsize/4)
generateDataset(d.dataset, d.epoch, cache)
}
// Disk storage is needed, this will get fancy
var endian string
if !isLittleEndian() {
endian = ".be"
}
path := filepath.Join(dir, fmt.Sprintf("full-R%d-%x%s", algorithmRevision, seed[:8], endian))
logger := log.New("epoch", d.epoch)
// Try to load the file from disk and memory map it
var err error
d.dump, d.mmap, d.dataset, err = memoryMap(path)
if err == nil {
logger.Debug("Loaded old ethash dataset from disk")
return
}
logger.Debug("Failed to load old ethash dataset", "err", err)
// No previous dataset available, create a new dataset file to fill
cache := make([]uint32, csize/4)
generateCache(cache, d.epoch, seed)
d.dump, d.mmap, d.dataset, err = memoryMapAndGenerate(path, dsize, func(buffer []uint32) { generateDataset(buffer, d.epoch, cache) })
if err != nil {
logger.Error("Failed to generate mapped ethash dataset", "err", err)
d.dataset = make([]uint32, dsize/2)
generateDataset(d.dataset, d.epoch, cache)
}
// Iterate over all previous instances and delete old ones
for ep := int(d.epoch) - limit; ep >= 0; ep-- {
seed := seedHash(uint64(ep)*epochLength + 1)
path := filepath.Join(dir, fmt.Sprintf("full-R%d-%x%s", algorithmRevision, seed[:8], endian))
os.Remove(path)
}
})
}
// release closes any file handlers and memory maps open.
func (d *dataset) release() {
if d.mmap != nil {
d.mmap.Unmap()
d.mmap = nil
}
if d.dump != nil {
d.dump.Close()
d.dump = nil
}
}
// MakeCache generates a new ethash cache and optionally stores it to disk.
func MakeCache(block uint64, dir string) {
c := cache{epoch: block / epochLength}
c.generate(dir, math.MaxInt32, false)
c.release()
}
// MakeDataset generates a new ethash dataset and optionally stores it to disk.
func MakeDataset(block uint64, dir string) {
d := dataset{epoch: block / epochLength}
d.generate(dir, math.MaxInt32, false)
d.release()
}
// Ethash is a consensus engine based on proot-of-work implementing the ethash
// algorithm.
type Ethash struct {
cachedir string // Data directory to store the verification caches
cachesinmem int // Number of caches to keep in memory
cachesondisk int // Number of caches to keep on disk
dagdir string // Data directory to store full mining datasets
dagsinmem int // Number of mining datasets to keep in memory
dagsondisk int // Number of mining datasets to keep on disk
caches map[uint64]*cache // In memory caches to avoid regenerating too often
fcache *cache // Pre-generated cache for the estimated future epoch
datasets map[uint64]*dataset // In memory datasets to avoid regenerating too often
fdataset *dataset // Pre-generated dataset for the estimated future epoch
// Mining related fields
rand *rand.Rand // Properly seeded random source for nonces
threads int // Number of threads to mine on if mining
update chan struct{} // Notification channel to update mining parameters
hashrate metrics.Meter // Meter tracking the average hashrate
// The fields below are hooks for testing
tester bool // Flag whether to use a smaller test dataset
shared *Ethash // Shared PoW verifier to avoid cache regeneration
fakeMode bool // Flag whether to disable PoW checking
fakeFull bool // Flag whether to disable all consensus rules
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
}
// New creates a full sized ethash PoW scheme.
func New(cachedir string, cachesinmem, cachesondisk int, dagdir string, dagsinmem, dagsondisk int) *Ethash {
if cachesinmem <= 0 {
log.Warn("One ethash cache must always be in memory", "requested", cachesinmem)
cachesinmem = 1
}
if cachedir != "" && cachesondisk > 0 {
log.Info("Disk storage enabled for ethash caches", "dir", cachedir, "count", cachesondisk)
}
if dagdir != "" && dagsondisk > 0 {
log.Info("Disk storage enabled for ethash DAGs", "dir", dagdir, "count", dagsondisk)
}
return &Ethash{
cachedir: cachedir,
cachesinmem: cachesinmem,
cachesondisk: cachesondisk,
dagdir: dagdir,
dagsinmem: dagsinmem,
dagsondisk: dagsondisk,
caches: make(map[uint64]*cache),
datasets: make(map[uint64]*dataset),
update: make(chan struct{}),
hashrate: metrics.NewMeter(),
}
}
// NewTester creates a small sized ethash PoW scheme useful only for testing
// purposes.
func NewTester() *Ethash {
return &Ethash{
cachesinmem: 1,
caches: make(map[uint64]*cache),
datasets: make(map[uint64]*dataset),
tester: true,
update: make(chan struct{}),
hashrate: metrics.NewMeter(),
}
}
// NewFaker creates a ethash consensus engine with a fake PoW scheme that accepts
// all blocks' seal as valid, though they still have to conform to the Ethereum
// consensus rules.
func NewFaker() *Ethash {
return &Ethash{fakeMode: true}
}
// NewFakeFailer creates a ethash consensus engine with a fake PoW scheme that
// accepts all blocks as valid apart from the single one specified, though they
// still have to conform to the Ethereum consensus rules.
func NewFakeFailer(fail uint64) *Ethash {
return &Ethash{fakeMode: true, fakeFail: fail}
}
// NewFakeDelayer creates a ethash consensus engine with a fake PoW scheme that
// accepts all blocks as valid, but delays verifications by some time, though
// they still have to conform to the Ethereum consensus rules.
func NewFakeDelayer(delay time.Duration) *Ethash {
return &Ethash{fakeMode: true, fakeDelay: delay}
}
// NewFullFaker creates an ethash consensus engine with a full fake scheme that
// accepts all blocks as valid, without checking any consensus rules whatsoever.
func NewFullFaker() *Ethash {
return &Ethash{fakeMode: true, fakeFull: true}
}
// NewShared creates a full sized ethash PoW shared between all requesters running
// in the same process.
func NewShared() *Ethash {
return &Ethash{shared: sharedEthash}
}
// 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.
func (ethash *Ethash) cache(block uint64) []uint32 {
epoch := block / epochLength
// If we have a PoW for that epoch, use that
ethash.lock.Lock()
current, future := ethash.caches[epoch], (*cache)(nil)
if current == nil {
// No in-memory cache, evict the oldest if the cache limit was reached
for len(ethash.caches) > 0 && len(ethash.caches) >= ethash.cachesinmem {
var evict *cache
for _, cache := range ethash.caches {
if evict == nil || evict.used.After(cache.used) {
evict = cache
}
}
delete(ethash.caches, evict.epoch)
evict.release()
log.Trace("Evicted ethash cache", "epoch", evict.epoch, "used", evict.used)
}
// If we have the new cache pre-generated, use that, otherwise create a new one
if ethash.fcache != nil && ethash.fcache.epoch == epoch {
log.Trace("Using pre-generated cache", "epoch", epoch)
current, ethash.fcache = ethash.fcache, nil
} else {
log.Trace("Requiring new ethash cache", "epoch", epoch)
current = &cache{epoch: epoch}
}
ethash.caches[epoch] = current
// If we just used up the future cache, or need a refresh, regenerate
if ethash.fcache == nil || ethash.fcache.epoch <= epoch {
if ethash.fcache != nil {
ethash.fcache.release()
}
log.Trace("Requiring new future ethash cache", "epoch", epoch+1)
future = &cache{epoch: epoch + 1}
ethash.fcache = future
}
// New current cache, set its initial timestamp
current.used = time.Now()
}
ethash.lock.Unlock()
// Wait for generation finish, bump the timestamp and finalize the cache
current.generate(ethash.cachedir, ethash.cachesondisk, ethash.tester)
current.lock.Lock()
current.used = time.Now()
current.lock.Unlock()
// If we exhausted the future cache, now's a good time to regenerate it
if future != nil {
go future.generate(ethash.cachedir, ethash.cachesondisk, ethash.tester)
}
return current.cache
}
// dataset tries to retrieve a mining dataset for the specified block number
// by first checking against a list of in-memory datasets, then against DAGs
// stored on disk, and finally generating one if none can be found.
func (ethash *Ethash) dataset(block uint64) []uint32 {
epoch := block / epochLength
// If we have a PoW for that epoch, use that
ethash.lock.Lock()
current, future := ethash.datasets[epoch], (*dataset)(nil)
if current == nil {
// No in-memory dataset, evict the oldest if the dataset limit was reached
for len(ethash.datasets) > 0 && len(ethash.datasets) >= ethash.dagsinmem {
var evict *dataset
for _, dataset := range ethash.datasets {
if evict == nil || evict.used.After(dataset.used) {
evict = dataset
}
}
delete(ethash.datasets, evict.epoch)
evict.release()
log.Trace("Evicted ethash dataset", "epoch", evict.epoch, "used", evict.used)
}
// If we have the new cache pre-generated, use that, otherwise create a new one
if ethash.fdataset != nil && ethash.fdataset.epoch == epoch {
log.Trace("Using pre-generated dataset", "epoch", epoch)
current = &dataset{epoch: ethash.fdataset.epoch} // Reload from disk
ethash.fdataset = nil
} else {
log.Trace("Requiring new ethash dataset", "epoch", epoch)
current = &dataset{epoch: epoch}
}
ethash.datasets[epoch] = current
// If we just used up the future dataset, or need a refresh, regenerate
if ethash.fdataset == nil || ethash.fdataset.epoch <= epoch {
if ethash.fdataset != nil {
ethash.fdataset.release()
}
log.Trace("Requiring new future ethash dataset", "epoch", epoch+1)
future = &dataset{epoch: epoch + 1}
ethash.fdataset = future
}
// New current dataset, set its initial timestamp
current.used = time.Now()
}
ethash.lock.Unlock()
// Wait for generation finish, bump the timestamp and finalize the cache
current.generate(ethash.dagdir, ethash.dagsondisk, ethash.tester)
current.lock.Lock()
current.used = time.Now()
current.lock.Unlock()
// If we exhausted the future dataset, now's a good time to regenerate it
if future != nil {
go future.generate(ethash.dagdir, ethash.dagsondisk, ethash.tester)
}
return current.dataset
}
// Threads returns the number of mining threads currently enabled. This doesn't
// necessarily mean that mining is running!
func (ethash *Ethash) Threads() int {
ethash.lock.Lock()
defer ethash.lock.Unlock()
return ethash.threads
}
// SetThreads updates the number of mining threads currently enabled. Calling
// this method does not start mining, only sets the thread count. If zero is
// specified, the miner will use all cores of the machine. Setting a thread
// count below zero is allowed and will cause the miner to idle, without any
// work being done.
func (ethash *Ethash) SetThreads(threads int) {
ethash.lock.Lock()
defer ethash.lock.Unlock()
// If we're running a shared PoW, set the thread count on that instead
if ethash.shared != nil {
ethash.shared.SetThreads(threads)
return
}
// Update the threads and ping any running seal to pull in any changes
ethash.threads = threads
select {
case ethash.update <- struct{}{}:
default:
}
}
// Hashrate implements PoW, returning the measured rate of the search invocations
// per second over the last minute.
func (ethash *Ethash) Hashrate() float64 {
return ethash.hashrate.Rate1()
}
// APIs implements consensus.Engine, returning the user facing RPC APIs. Currently
// that is empty.
func (ethash *Ethash) APIs(chain consensus.ChainReader) []rpc.API {
return nil
}
// SeedHash is the seed to use for generating a verification cache and the mining
// dataset.
func SeedHash(block uint64) []byte {
return seedHash(block)
}
