From a55e36fb0c514f9c831977c404a60f54ab6ec618 Mon Sep 17 00:00:00 2001
From: jules01 <iulian.pascalau@gmail.com>
Date: Mon, 24 Oct 2022 15:48:28 +0300
Subject: [PATCH 1/2] - fixed concurrency issues on transaction simulator

---
 process/txsimulator/txSimulator.go      |  5 ++++
 process/txsimulator/txSimulator_test.go | 34 +++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/process/txsimulator/txSimulator.go b/process/txsimulator/txSimulator.go
index 851ffea5e3d..cdf18b31b10 100644
--- a/process/txsimulator/txSimulator.go
+++ b/process/txsimulator/txSimulator.go
@@ -2,6 +2,7 @@ package txsimulator
 
 import (
 	"encoding/hex"
+	"sync"
 
 	"github.com/ElrondNetwork/elrond-go-core/core"
 	"github.com/ElrondNetwork/elrond-go-core/core/check"
@@ -30,6 +31,7 @@ type ArgsTxSimulator struct {
 }
 
 type transactionSimulator struct {
+	mutCriticalSection     sync.Mutex
 	txProcessor            TransactionProcessor
 	intermProcContainer    process.IntermediateProcessorContainer
 	addressPubKeyConverter core.PubkeyConverter
@@ -76,6 +78,9 @@ func NewTransactionSimulator(args ArgsTxSimulator) (*transactionSimulator, error
 
 // ProcessTx will process the transaction in a special environment, where state-writing is not allowed
 func (ts *transactionSimulator) ProcessTx(tx *transaction.Transaction) (*txSimData.SimulationResults, error) {
+	ts.mutCriticalSection.Lock()
+	defer ts.mutCriticalSection.Unlock()
+
 	txStatus := transaction.TxStatusPending
 	failReason := ""
 
diff --git a/process/txsimulator/txSimulator_test.go b/process/txsimulator/txSimulator_test.go
index 031093ecbe1..a79bdcfd56b 100644
--- a/process/txsimulator/txSimulator_test.go
+++ b/process/txsimulator/txSimulator_test.go
@@ -3,7 +3,9 @@ package txsimulator
 import (
 	"encoding/hex"
 	"errors"
+	"sync"
 	"testing"
+	"time"
 
 	"github.com/ElrondNetwork/elrond-go-core/core"
 	"github.com/ElrondNetwork/elrond-go-core/data"
@@ -18,6 +20,7 @@ import (
 	"github.com/ElrondNetwork/elrond-go/testscommon"
 	"github.com/ElrondNetwork/elrond-go/testscommon/hashingMocks"
 	vmcommon "github.com/ElrondNetwork/elrond-vm-common"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -228,3 +231,34 @@ func getTxSimulatorArgs() ArgsTxSimulator {
 		Hasher:                    &hashingMocks.HasherMock{},
 	}
 }
+
+func TestTransactionSimulator_ProcessTxConcurrentCalls(t *testing.T) {
+	t.Parallel()
+
+	numTransactionProcessorCalls := 0
+	args := getTxSimulatorArgs()
+	args.TransactionProcessor = &testscommon.TxProcessorStub{
+		ProcessTransactionCalled: func(transaction *transaction.Transaction) (vmcommon.ReturnCode, error) {
+			// deliberately not used a mutex here as to catch race conditions
+			numTransactionProcessorCalls++
+
+			return vmcommon.Ok, nil
+		},
+	}
+	txSimulator, _ := NewTransactionSimulator(args)
+	tx := &transaction.Transaction{Nonce: 37}
+
+	numCalls := 100
+	wg := sync.WaitGroup{}
+	wg.Add(numCalls)
+	for i := 0; i < numCalls; i++ {
+		go func(idx int) {
+			time.Sleep(time.Millisecond * 10)
+			_, _ = txSimulator.ProcessTx(tx)
+			wg.Done()
+		}(i)
+	}
+
+	wg.Wait()
+	assert.Equal(t, numCalls, numTransactionProcessorCalls)
+}

From 755cf88314ee94717b47c8e2c1537568b260ffba Mon Sep 17 00:00:00 2001
From: jules01 <iulian.pascalau@gmail.com>
Date: Mon, 24 Oct 2022 15:56:00 +0300
Subject: [PATCH 2/2] - renamed mutex

---
 process/txsimulator/txSimulator.go | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/process/txsimulator/txSimulator.go b/process/txsimulator/txSimulator.go
index cdf18b31b10..7ada4477f6e 100644
--- a/process/txsimulator/txSimulator.go
+++ b/process/txsimulator/txSimulator.go
@@ -31,7 +31,7 @@ type ArgsTxSimulator struct {
 }
 
 type transactionSimulator struct {
-	mutCriticalSection     sync.Mutex
+	mutOperation           sync.Mutex
 	txProcessor            TransactionProcessor
 	intermProcContainer    process.IntermediateProcessorContainer
 	addressPubKeyConverter core.PubkeyConverter
@@ -78,8 +78,8 @@ func NewTransactionSimulator(args ArgsTxSimulator) (*transactionSimulator, error
 
 // ProcessTx will process the transaction in a special environment, where state-writing is not allowed
 func (ts *transactionSimulator) ProcessTx(tx *transaction.Transaction) (*txSimData.SimulationResults, error) {
-	ts.mutCriticalSection.Lock()
-	defer ts.mutCriticalSection.Unlock()
+	ts.mutOperation.Lock()
+	defer ts.mutOperation.Unlock()
 
 	txStatus := transaction.TxStatusPending
 	failReason := ""