core, consensus: pluggable consensus engines (#3817)

This commit adds pluggable consensus engines to go-ethereum. In short, it
introduces a generic consensus interface, and refactors the entire codebase to
use this interface.

1 files changed, 587 insertions, 0 deletions

diff --git a/consensus/ethash/ethash.go b/consensus/ethash/ethash.go
new file mode 100644
index 000000000..aa5b2d8a0
--- /dev/null
+++ b/consensus/ethash/ethash.go
@@ -0,0 +1,587 @@
+// 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.Flush(); err != nil {
+		mem.Unmap()
+		dump.Close()
+		return nil, nil, nil, err
+	}
+	os.Rename(temp, path)
+	return dump, mem, data, nil
+}
+
+// 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 + 1}
+	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 + 1}
+	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 alwast 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 a 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
+		}
+	}
+	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
+		}
+	}
+	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.
+func (ethash *Ethash) SetThreads(threads int) {
+	ethash.lock.Lock()
+	defer ethash.lock.Unlock()
+
+	// 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)
+}