fix to pass mut in stead of reading it again (#114)

jsonrpc/backend/backend.go

@@ -192,7 +192,7 @@ type AccMut struct {
 
 // acquireAccMut acquires the mutex for the account with the given senderHex
 // and increments the reference count. If the mutex does not exist, it is created.
-func (b *JSONRPCBackend) acquireAccMut(senderHex string) {
+func (b *JSONRPCBackend) acquireAccMut(senderHex string) *AccMut {
 	// critical section for rc and create
 	b.mut.Lock()
 	accMut, ok := b.accMuts[senderHex]
@@ -205,13 +205,13 @@ func (b *JSONRPCBackend) acquireAccMut(senderHex string) {
 	// critical section end
 
 	accMut.mut.Lock()
+	return accMut
 }
 
 // releaseAccMut releases the mutex for the account with the given senderHex
 // and decrements the reference count. If the reference count reaches zero,
 // the mutex is deleted.
-func (b *JSONRPCBackend) releaseAccMut(senderHex string) {
-	accMut := b.accMuts[senderHex]
+func (b *JSONRPCBackend) releaseAccMut(senderHex string, accMut *AccMut) {
 	accMut.mut.Unlock()
 
 	// critical section for rc and delete

jsonrpc/backend/tx.go

@@ -71,8 +71,8 @@ func (b *JSONRPCBackend) SendTx(tx *coretypes.Transaction) error {
 	senderHex := hexutil.Encode(sender.Bytes())
 
 	// hold mutex for each sender
-	b.acquireAccMut(senderHex)
-	defer b.releaseAccMut(senderHex)
+	accMut := b.acquireAccMut(senderHex)
+	defer b.releaseAccMut(senderHex, accMut)
 
 	checkCtx := b.app.GetContextForCheckTx(nil)
 	if acc := b.app.AccountKeeper.GetAccount(checkCtx, sender); acc != nil {