Rework and improve async script validation logic.

The previous script validation logic entailed starting up a hard-coded
number of goroutines to process the transaction scripts in parallel.  In
particular, one goroutine (up to 8 max) was started per transaction in a
block and another one was started for each input script pair in the
each transaction.  This resulted in 64 goroutines simultaneously running
scripts and verifying cryptographic signatures.  This could easily lead to
the overall system feeling sluggish.

Further the previous design could also result in bursty behavior since the
number of inputs to a transaction as well as its complexity can vary
widely between transactions.  For example, starting 2 goroutines (one to
process the transaction and one for actual script pair validation) to
verify a transaction with a single input was not desirable.

Finally, the previous design validated all transactions and inputs
regardless of a failure in one of the other scripts.  This really didn't
have a big impact since it's quite rare that blocks with invalid
verifications are being processed, but it was a potential way DoS vector.

This commit changes the logic in a few ways to improve things:

- The max number of validation goroutines is now based on the number of
  cores in the system
- All transaction inputs from all transactions in the block are collated
  into a single list which is fed through the aforementioned validation
  goroutines
- The validation CPU usage is much more consistent due to the collation of
  inputs
- A validation error in any goroutine immediately stops validation of all
  remaining inputs
- The errors have been improved to include context about what tx script
  pair failed as opposed to showing the information as a warning

This closes conformal/btcd#59.

scriptval.go

@@ -10,108 +10,199 @@ import (
 	"github.com/conformal/btcutil"
 	"github.com/conformal/btcwire"
 	"math"
+	"runtime"
 )
 
-// txValidate is used to track results of validating scripts for each
+// txValidateItem holds a transaction along with which input to validate.
-// transaction input index.
+type txValidateItem struct {
-type txValidate struct {
+	txInIndex int
-	txIndex int
+	txIn      *btcwire.TxIn
-	err     error
+	tx        *btcutil.Tx
 }
 
-// validateTxIn validates a the script pair for the passed spending transaction
+// txValidator provides a type which asynchronously validates transaction
-// (along with the specific input index) and origin transaction (with the
+// inputs.  It provides several channels for communication and a processing
-// specific output index).
+// function that is intended to be in run multiple goroutines.
-func validateTxIn(txInIdx int, txin *btcwire.TxIn, tx *btcutil.Tx, originTx *btcutil.Tx, flags btcscript.ScriptFlags) error {
+type txValidator struct {
-	// If the input transaction has no previous input, there is nothing
+	validateChan chan *txValidateItem
-	// to check.
+	quitChan     chan bool
-	originTxIdx := txin.PreviousOutpoint.Index
+	resultChan   chan error
-	if originTxIdx == math.MaxUint32 {
+	txStore      TxStore
+	flags        btcscript.ScriptFlags
+}
+
+// sendResult sends the result of a script pair validation on the internal
+// result channel while respecting the quit channel.  The allows orderly
+// shutdown when the validation process is aborted early due to a validation
+// error in one of the other goroutines.
+func (v *txValidator) sendResult(result error) {
+	select {
+	case v.resultChan <- result:
+	case <-v.quitChan:
+	}
+}
+
+// validateHandler consumes items to validate from the internal validate channel
+// and returns the result of the validation on the internal result channel. It
+// must be run as a goroutine.
+func (v *txValidator) validateHandler() {
+out:
+	for {
+		select {
+		case txVI := <-v.validateChan:
+			// Ensure the referenced input transaction is available.
+			//txIn := txVI.tx.MsgTx().TxIn[txVI.txInIdx]
+			txIn := txVI.txIn
+			txInHash := &txIn.PreviousOutpoint.Hash
+			originTx, exists := v.txStore[*txInHash]
+			if !exists || originTx.Err != nil || originTx.Tx == nil {
+				err := fmt.Errorf("unable to find input "+
+					"transaction %v referenced from "+
+					"transaction %v", txInHash,
+					txVI.tx.Sha())
+				v.sendResult(err)
+				break out
+			}
+			originMsgTx := originTx.Tx.MsgTx()
+
+			// Ensure the output index in the referenced transaction
+			// is available.
+			originTxIndex := txIn.PreviousOutpoint.Index
+			if originTxIndex >= uint32(len(originMsgTx.TxOut)) {
+				err := fmt.Errorf("out of bounds "+
+					"input index %d in transaction %v "+
+					"referenced from transaction %v",
+					originTxIndex, txInHash, txVI.tx.Sha())
+				v.sendResult(err)
+				break out
+			}
+
+			// Create a new script engine for the script pair.
+			sigScript := txIn.SignatureScript
+			pkScript := originMsgTx.TxOut[originTxIndex].PkScript
+			engine, err := btcscript.NewScript(sigScript, pkScript,
+				txVI.txInIndex, txVI.tx.MsgTx(), v.flags)
+			if err != nil {
+				v.sendResult(err)
+				break out
+			}
+
+			// Execute the script pair.
+			if err := engine.Execute(); err != nil {
+				err := fmt.Errorf("validate of input "+
+					"%d failed: %v", txVI.txInIndex, err)
+				v.sendResult(err)
+				break out
+			}
+
+			// Validation succeeded.
+			v.sendResult(nil)
+
+		case <-v.quitChan:
+			break out
+		}
+	}
+}
+
+// Validate validates the scripts for all of the passed transaction inputs using
+// multiple goroutines.
+func (v *txValidator) Validate(items []*txValidateItem) error {
+	if len(items) == 0 {
 		return nil
 	}
 
-	if originTxIdx >= uint32(len(originTx.MsgTx().TxOut)) {
+	// Limit the number of goroutines to do script validation based on the
-		originTxSha := &txin.PreviousOutpoint.Hash
+	// number of processor cores.  This help ensure the system stays
-		log.Warnf("unable to locate source tx %v spending tx %v",
+	// reasonably responsive under heavy load.
-			originTxSha, tx.Sha())
+	maxGoRoutines := runtime.NumCPU() * 3
-		return fmt.Errorf("invalid index %x", originTxIdx)
+	if maxGoRoutines <= 0 {
+		maxGoRoutines = 1
+	}
+	if maxGoRoutines > len(items) {
+		maxGoRoutines = len(items)
 	}
 
-	sigScript := txin.SignatureScript
+	// Start up validation handlers that are used to asynchronously
-	pkScript := originTx.MsgTx().TxOut[originTxIdx].PkScript
+	// validate each transaction input.
-	engine, err := btcscript.NewScript(sigScript, pkScript, txInIdx,
+	for i := 0; i < maxGoRoutines; i++ {
-		tx.MsgTx(), flags)
+		go v.validateHandler()
-	if err != nil {
-		return err
 	}
 
-	err = engine.Execute()
+	// Validate each of the inputs.  The quit channel is closed when any
-	if err != nil {
+	// errors occur so all processing goroutines exit regardless of which
-		log.Warnf("validate of input %v failed: %v", txInIdx, err)
+	// input had the validation error.
-		return err
+	numInputs := len(items)
+	currentItem := 0
+	processedItems := 0
+	for processedItems < numInputs {
+		// Only send items while there are still items that need to
+		// be processed.  The select statement will never select a nil
+		// channel.
+		var validateChan chan *txValidateItem
+		var item *txValidateItem
+		if currentItem < numInputs {
+			validateChan = v.validateChan
+			item = items[currentItem]
+		}
+
+		select {
+		case validateChan <- item:
+			currentItem++
+
+		case err := <-v.resultChan:
+			processedItems++
+			if err != nil {
+				close(v.quitChan)
+				return err
+			}
+		}
 	}
 
+	close(v.quitChan)
 	return nil
 }
 
+// newTxValidator returns a new instance of txValidator to be used for
+// validating transaction scripts asynchronously.
+func newTxValidator(txStore TxStore, flags btcscript.ScriptFlags) *txValidator {
+	return &txValidator{
+		validateChan: make(chan *txValidateItem),
+		quitChan:     make(chan bool),
+		resultChan:   make(chan error),
+		txStore:      txStore,
+		flags:        flags,
+	}
+}
+
 // ValidateTransactionScripts validates the scripts for the passed transaction
 // using multiple goroutines.
-func ValidateTransactionScripts(tx *btcutil.Tx, txStore TxStore, flags btcscript.ScriptFlags) (err error) {
+func ValidateTransactionScripts(tx *btcutil.Tx, txStore TxStore, flags btcscript.ScriptFlags) error {
-	c := make(chan txValidate)
+	// Collect all of the transaction inputs and required information for
-	job := tx.MsgTx().TxIn
+	// validation.
-	resultErrors := make([]error, len(job))
+	txIns := tx.MsgTx().TxIn
-
+	txValItems := make([]*txValidateItem, 0, len(txIns))
-	var currentItem int
+	for txInIdx, txIn := range txIns {
-	var completedItems int
+		// Skip coinbases.
-
+		if txIn.PreviousOutpoint.Index == math.MaxUint32 {
-	processFunc := func(txInIdx int) {
+			continue
-		log.Tracef("validating tx %v input %v len %v",
-			tx.Sha(), txInIdx, len(job))
-		txin := job[txInIdx]
-		originTxSha := &txin.PreviousOutpoint.Hash
-		origintxidx := txin.PreviousOutpoint.Index
-
-		var originTx *btcutil.Tx
-		if origintxidx != math.MaxUint32 {
-			txInfo, ok := txStore[*originTxSha]
-			if !ok {
-				//wtf?
-				fmt.Printf("obj not found in txStore %v",
-					originTxSha)
-			}
-			originTx = txInfo.Tx
 		}
-		err := validateTxIn(txInIdx, txin, tx, originTx, flags)
-		r := txValidate{txInIdx, err}
-		c <- r
-	}
-	for currentItem = 0; currentItem < len(job) && currentItem < 16; currentItem++ {
-		go processFunc(currentItem)
-	}
-	for completedItems < len(job) {
-		select {
-		case result := <-c:
-			completedItems++
-			resultErrors[result.txIndex] = result.err
-			// would be nice to determine if we could stop
-			// on early errors here instead of running more.
-			if err == nil {
-				err = result.err
-			}
 
-			if currentItem < len(job) {
+		txVI := &txValidateItem{
-				go processFunc(currentItem)
+			txInIndex: txInIdx,
-				currentItem++
+			txIn:      txIn,
-			}
+			tx:        tx,
 		}
+		txValItems = append(txValItems, txVI)
 	}
-	for i := 0; i < len(job); i++ {
+
-		if resultErrors[i] != nil {
+	// Validate all of the inputs.
-			log.Warnf("tx %v failed input %v, err %v", tx.Sha(), i,
+	validator := newTxValidator(txStore, flags)
-				resultErrors[i])
+	if err := validator.Validate(txValItems); err != nil {
-		}
+		return err
 	}
-	return
+
+	return nil
+
 }
 
 // checkBlockScripts executes and validates the scripts for all transactions in
@@ -124,38 +215,33 @@ func checkBlockScripts(block *btcutil.Block, txStore TxStore) error {
 		flags |= btcscript.ScriptBip16
 	}
 
-	txList := block.Transactions()
+	// Collect all of the transaction inputs and required information for
-	c := make(chan txValidate)
+	// validation for all transactions in the block into a single slice.
-	resultErrors := make([]error, len(txList))
+	numInputs := 0
-
+	for _, tx := range block.Transactions() {
-	var currentItem int
+		numInputs += len(tx.MsgTx().TxIn)
-	var completedItems int
-	processFunc := func(txIdx int) {
-		err := ValidateTransactionScripts(txList[txIdx], txStore, flags)
-		r := txValidate{txIdx, err}
-		c <- r
 	}
-	for currentItem = 0; currentItem < len(txList) && currentItem < 8; currentItem++ {
+	txValItems := make([]*txValidateItem, 0, numInputs)
-		go processFunc(currentItem)
+	for _, tx := range block.Transactions() {
-	}
+		for txInIdx, txIn := range tx.MsgTx().TxIn {
-	for completedItems < len(txList) {
+			// Skip coinbases.
-		select {
+			if txIn.PreviousOutpoint.Index == math.MaxUint32 {
-		case result := <-c:
+				continue
-			completedItems++
-			resultErrors[result.txIndex] = result.err
-			// would be nice to determine if we could stop
-			// on early errors here instead of running more.
-
-			if currentItem < len(txList) {
-				go processFunc(currentItem)
-				currentItem++
 			}
+
+			txVI := &txValidateItem{
+				txInIndex: txInIdx,
+				txIn:      txIn,
+				tx:        tx,
+			}
+			txValItems = append(txValItems, txVI)
 		}
 	}
-	for i := 0; i < len(txList); i++ {
+
-		if resultErrors[i] != nil {
+	// Validate all of the inputs.
-			return resultErrors[i]
+	validator := newTxValidator(txStore, flags)
-		}
+	if err := validator.Validate(txValItems); err != nil {
+		return err
 	}
 
 	return nil