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, 37 insertions, 112 deletions

diff --git a/core/headerchain.go b/core/headerchain.go
index e7660cc60..e2d0ff5b1 100644
--- a/core/headerchain.go
+++ b/core/headerchain.go
@@ -18,21 +18,19 @@ package core
 
 import (
 	crand "crypto/rand"
+	"errors"
 	"fmt"
 	"math"
 	"math/big"
 	mrand "math/rand"
-	"runtime"
-	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
-	"github.com/ethereum/go-ethereum/pow"
 	"github.com/hashicorp/golang-lru"
 )
 
@@ -62,18 +60,15 @@ type HeaderChain struct {
 
 	procInterrupt func() bool
 
-	rand         *mrand.Rand
-	getValidator getHeaderValidatorFn
+	rand   *mrand.Rand
+	engine consensus.Engine
 }
 
-// getHeaderValidatorFn returns a HeaderValidator interface
-type getHeaderValidatorFn func() HeaderValidator
-
 // NewHeaderChain creates a new HeaderChain structure.
 //  getValidator should return the parent's validator
 //  procInterrupt points to the parent's interrupt semaphore
 //  wg points to the parent's shutdown wait group
-func NewHeaderChain(chainDb ethdb.Database, config *params.ChainConfig, getValidator getHeaderValidatorFn, procInterrupt func() bool) (*HeaderChain, error) {
+func NewHeaderChain(chainDb ethdb.Database, config *params.ChainConfig, engine consensus.Engine, procInterrupt func() bool) (*HeaderChain, error) {
 	headerCache, _ := lru.New(headerCacheLimit)
 	tdCache, _ := lru.New(tdCacheLimit)
 	numberCache, _ := lru.New(numberCacheLimit)
@@ -92,7 +87,7 @@ func NewHeaderChain(chainDb ethdb.Database, config *params.ChainConfig, getValid
 		numberCache:   numberCache,
 		procInterrupt: procInterrupt,
 		rand:          mrand.New(mrand.NewSource(seed.Int64())),
-		getValidator:  getValidator,
+		engine:        engine,
 	}
 
 	hc.genesisHeader = hc.GetHeaderByNumber(0)
@@ -228,78 +223,34 @@ func (hc *HeaderChain) ValidateHeaderChain(chain []*types.Header, checkFreq int)
 		}
 	}
 
-	// Generate the list of headers that should be POW verified
-	verify := make([]bool, len(chain))
-	for i := 0; i < len(verify)/checkFreq; i++ {
+	// Generate the list of seal verification requests, and start the parallel verifier
+	seals := make([]bool, len(chain))
+	for i := 0; i < len(seals)/checkFreq; i++ {
 		index := i*checkFreq + hc.rand.Intn(checkFreq)
-		if index >= len(verify) {
-			index = len(verify) - 1
+		if index >= len(seals) {
+			index = len(seals) - 1
 		}
-		verify[index] = true
-	}
-	verify[len(verify)-1] = true // Last should always be verified to avoid junk
-
-	// Create the header verification task queue and worker functions
-	tasks := make(chan int, len(chain))
-	for i := 0; i < len(chain); i++ {
-		tasks <- i
+		seals[index] = true
 	}
-	close(tasks)
+	seals[len(seals)-1] = true // Last should always be verified to avoid junk
 
-	errs, failed := make([]error, len(tasks)), int32(0)
-	process := func(worker int) {
-		for index := range tasks {
-			header, hash := chain[index], chain[index].Hash()
+	abort, results := hc.engine.VerifyHeaders(hc, chain, seals)
+	defer close(abort)
 
-			// Short circuit insertion if shutting down or processing failed
-			if hc.procInterrupt() {
-				return
-			}
-			if atomic.LoadInt32(&failed) > 0 {
-				return
-			}
-			// Short circuit if the header is bad or already known
-			if BadHashes[hash] {
-				errs[index] = BadHashError(hash)
-				atomic.AddInt32(&failed, 1)
-				return
-			}
-			if hc.HasHeader(hash) {
-				continue
-			}
-			// Verify that the header honors the chain parameters
-			checkPow := verify[index]
-
-			var err error
-			if index == 0 {
-				err = hc.getValidator().ValidateHeader(header, hc.GetHeader(header.ParentHash, header.Number.Uint64()-1), checkPow)
-			} else {
-				err = hc.getValidator().ValidateHeader(header, chain[index-1], checkPow)
-			}
-			if err != nil {
-				errs[index] = err
-				atomic.AddInt32(&failed, 1)
-				return
-			}
+	// Iterate over the headers and ensure they all check out
+	for i, header := range chain {
+		// If the chain is terminating, stop processing blocks
+		if hc.procInterrupt() {
+			log.Debug("Premature abort during headers verification")
+			return 0, errors.New("aborted")
 		}
-	}
-	// Start as many worker threads as goroutines allowed
-	pending := new(sync.WaitGroup)
-	for i := 0; i < runtime.GOMAXPROCS(0); i++ {
-		pending.Add(1)
-		go func(id int) {
-			defer pending.Done()
-			process(id)
-		}(i)
-	}
-	pending.Wait()
-
-	// If anything failed, report
-	if failed > 0 {
-		for i, err := range errs {
-			if err != nil {
-				return i, err
-			}
+		// If the header is a banned one, straight out abort
+		if BadHashes[header.Hash()] {
+			return i, BadHashError(header.Hash())
+		}
+		// Otherwise wait for headers checks and ensure they pass
+		if err := <-results; err != nil {
+			return i, err
 		}
 	}
 
@@ -313,13 +264,11 @@ func (hc *HeaderChain) InsertHeaderChain(chain []*types.Header, writeHeader WhCa
 	for i, header := range chain {
 		// Short circuit insertion if shutting down
 		if hc.procInterrupt() {
-			log.Debug("Premature abort during headers processing")
-			break
+			log.Debug("Premature abort during headers import")
+			return i, errors.New("aborted")
 		}
-		hash := header.Hash()
-
 		// If the header's already known, skip it, otherwise store
-		if hc.HasHeader(hash) {
+		if hc.GetHeader(header.Hash(), header.Number.Uint64()) != nil {
 			stats.ignored++
 			continue
 		}
@@ -490,35 +439,11 @@ func (hc *HeaderChain) SetGenesis(head *types.Header) {
 	hc.genesisHeader = head
 }
 
-// headerValidator is responsible for validating block headers
-//
-// headerValidator implements HeaderValidator.
-type headerValidator struct {
-	config *params.ChainConfig
-	hc     *HeaderChain // Canonical header chain
-	Pow    pow.PoW      // Proof of work used for validating
-}
-
-// NewBlockValidator returns a new block validator which is safe for re-use
-func NewHeaderValidator(config *params.ChainConfig, chain *HeaderChain, pow pow.PoW) HeaderValidator {
-	return &headerValidator{
-		config: config,
-		Pow:    pow,
-		hc:     chain,
-	}
-}
+// Config retrieves the header chain's chain configuration.
+func (hc *HeaderChain) Config() *params.ChainConfig { return hc.config }
 
-// ValidateHeader validates the given header and, depending on the pow arg,
-// checks the proof of work of the given header. Returns an error if the
-// validation failed.
-func (v *headerValidator) ValidateHeader(header, parent *types.Header, checkPow bool) error {
-	// Short circuit if the parent is missing.
-	if parent == nil {
-		return ParentError(header.ParentHash)
-	}
-	// Short circuit if the header's already known or its parent missing
-	if v.hc.HasHeader(header.Hash()) {
-		return nil
-	}
-	return ValidateHeader(v.config, v.Pow, header, parent, checkPow, false)
+// GetBlock implements consensus.ChainReader, and returns nil for every input as
+// a header chain does not have blocks available for retrieval.
+func (hc *HeaderChain) GetBlock(hash common.Hash, number uint64) *types.Block {
+	return nil
 }