FAB-16687 reduce mutex contention in validator

There is a mutex that guards the construction of []sync.Once, and the
level of contention is currently O(n^2), which can be reduced to O(n)
by trivial changes.

Change-Id: I9522eeebf6998ca7403c4033bac5932298ce8067
Signed-off-by: Jay Guo <guojiannan1101@gmail.com>

core/common/validation/statebased/validator_keylevel.go

@@ -181,18 +181,6 @@ func NewKeyLevelValidator(evaluator RWSetPolicyEvaluatorFactory, vpmgr KeyLevelV
 	}
 }
 
-func (klv *KeyLevelValidator) invokeOnce(block *common.Block, txnum uint64) *sync.Once {
-	klv.blockDep.mutex.Lock()
-	defer klv.blockDep.mutex.Unlock()
-
-	if klv.blockDep.blockNum != block.Header.Number {
-		klv.blockDep.blockNum = block.Header.Number
-		klv.blockDep.txDepOnce = make([]sync.Once, len(block.Data.Data))
-	}
-
-	return &klv.blockDep.txDepOnce[txnum]
-}
-
 func (klv *KeyLevelValidator) extractDependenciesForTx(blockNum, txNum uint64, envelopeBytes []byte) {
 	env, err := protoutil.GetEnvelopeFromBlock(envelopeBytes)
 	if err != nil {
@@ -235,10 +223,17 @@ func (klv *KeyLevelValidator) extractDependenciesForTx(blockNum, txNum uint64, e
 
 // PreValidate implements the function of the StateBasedValidator interface
 func (klv *KeyLevelValidator) PreValidate(txNum uint64, block *common.Block) {
+	klv.blockDep.mutex.Lock()
+	if klv.blockDep.blockNum != block.Header.Number {
+		klv.blockDep.blockNum = block.Header.Number
+		klv.blockDep.txDepOnce = make([]sync.Once, len(block.Data.Data))
+	}
+	klv.blockDep.mutex.Unlock()
+
 	for i := int64(txNum); i >= 0; i-- {
 		txPosition := uint64(i)
 
-		klv.invokeOnce(block, txPosition).Do(
+		klv.blockDep.txDepOnce[i].Do(
 			func() {
 				klv.extractDependenciesForTx(block.Header.Number, txPosition, block.Data.Data[txPosition])
 			})