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.

consensus/ethash/sealer.go

@@ -0,0 +1,146 @@
+// 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
+
+import (
+	crand "crypto/rand"
+	"math"
+	"math/big"
+	"math/rand"
+	"runtime"
+	"sync"
+
+	"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"
+)
+
+// 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) {
+	// If we're running a fake PoW, simply return a 0 nonce immediately
+	if ethash.fakeMode {
+		header := block.Header()
+		header.Nonce, header.MixDigest = types.BlockNonce{}, common.Hash{}
+		return block.WithSeal(header), nil
+	}
+	// If we're running a shared PoW, delegate sealing to it
+	if ethash.shared != nil {
+		return ethash.shared.Seal(chain, 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
+	if ethash.rand == nil {
+		seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
+		if err != nil {
+			ethash.lock.Unlock()
+			return nil, err
+		}
+		ethash.rand = rand.New(rand.NewSource(seed.Int64()))
+	}
+	ethash.lock.Unlock()
+	if threads == 0 {
+		threads = runtime.NumCPU()
+	}
+	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)
+		}(i, uint64(ethash.rand.Int63()))
+	}
+	// Wait until sealing is terminated or a nonce is found
+	var result *types.Block
+	select {
+	case <-stop:
+		// Outside abort, stop all miner threads
+		close(abort)
+	case result = <-found:
+		// One of the threads found a block, abort all others
+		close(abort)
+	case <-ethash.update:
+		// Thread count was changed on user request, restart
+		close(abort)
+		pend.Wait()
+		return ethash.Seal(chain, block, stop)
+	}
+	// Wait for all miners to terminate and return the block
+	pend.Wait()
+	return result, nil
+}
+
+// mine is the actual proof-of-work miner that searches for a nonce starting from
+// seed that results in correct final block difficulty.
+func (ethash *Ethash) mine(block *types.Block, id int, seed uint64, abort chan struct{}, found chan *types.Block) {
+	// Extract some data from the header
+	var (
+		header = block.Header()
+		hash   = header.HashNoNonce().Bytes()
+		target = new(big.Int).Div(maxUint256, header.Difficulty)
+
+		number  = header.Number.Uint64()
+		dataset = ethash.dataset(number)
+	)
+	// Start generating random nonces until we abort or find a good one
+	var (
+		attempts = int64(0)
+		nonce    = seed
+	)
+	logger := log.New("miner", id)
+	logger.Trace("Started ethash search for new nonces", "seed", seed)
+	for {
+		select {
+		case <-abort:
+			// Mining terminated, update stats and abort
+			logger.Trace("Ethash nonce search aborted", "attempts", nonce-seed)
+			ethash.hashrate.Mark(attempts)
+			return
+
+		default:
+			// We don't have to update hash rate on every nonce, so update after after 2^X nonces
+			attempts++
+			if (attempts % (1 << 15)) == 0 {
+				ethash.hashrate.Mark(attempts)
+				attempts = 0
+			}
+			// Compute the PoW value of this nonce
+			digest, result := hashimotoFull(dataset, hash, nonce)
+			if new(big.Int).SetBytes(result).Cmp(target) <= 0 {
+				// Correct nonce found, create a new header with it
+				header = types.CopyHeader(header)
+				header.Nonce = types.EncodeNonce(nonce)
+				header.MixDigest = common.BytesToHash(digest)
+
+				// Seal and return a block (if still needed)
+				select {
+				case found <- block.WithSeal(header):
+					logger.Trace("Ethash nonce found and reported", "attempts", nonce-seed, "nonce", nonce)
+				case <-abort:
+					logger.Trace("Ethash nonce found but discarded", "attempts", nonce-seed, "nonce", nonce)
+				}
+				return
+			}
+			nonce++
+		}
+	}
+}