fix: add wait group to handle message (#77)

## Description


This PR adds wait group to handle messages concurrently. 

Background: 
When I used `parse blocks`cmd to parse 1 specific height that has transactions & messages,  the messages can be lost because of being handled through go routines and when the main program is done, all go routines are closed. 

## Checklist
- [x] Targeted PR against correct branch.
- [ ] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
- [ ] Wrote unit tests.  
- [x] Re-reviewed `Files changed` in the Github PR explorer.

CHANGELOG.md

@@ -4,6 +4,7 @@
 - ([\#74](https://github.com/forbole/juno/pull/74)) Added database block count to prometheus to improve alert monitoring
 - ([\#75](https://github.com/forbole/juno/pull/75)) Allow modules to handle MsgExec inner messages
 - ([\#76](https://github.com/forbole/juno/pull/76)) Return 0 as height for `GetLastBlockHeight()` method if there are no blocks saved in database
+- ([\#77](https://github.com/forbole/juno/pull/77)) Add wait group to handle messages concurrently
 - ([\#79](https://github.com/forbole/juno/pull/79)) Use `sqlx` instead of `sql` while dealing with a PostgreSQL database
 - ([\#83](https://github.com/forbole/juno/pull/83)) Bump `github.com/tendermint/tendermint` to `v0.34.22`
 

database/postgresql/postgresql.go

@@ -101,7 +101,12 @@ func (db *Database) GetLastBlockHeight() (int64, error) {
 	stmt := `SELECT height FROM block ORDER BY height DESC LIMIT 1;`
 
 	var height int64
-	if err := db.SQL.QueryRow(stmt).Scan(&height); err != nil {
+	err := db.SQL.QueryRow(stmt).Scan(&height)
+	if err != nil {
+		if strings.Contains(err.Error(), "no rows in result set") {
+			// If no rows stored in block table, return 0 as height
+			return 0, nil
+		}
 		return 0, fmt.Errorf("error while getting last block height, error: %s", err)
 	}
 

parser/worker.go

@@ -3,6 +3,7 @@ package parser
 import (
 	"encoding/json"
 	"fmt"
+	"sync"
 	"time"
 
 	"github.com/cosmos/cosmos-sdk/x/authz"
@@ -327,18 +328,23 @@ func (w Worker) handleMessage(index int, msg sdk.Msg, tx *types.Tx) {
 // ExportTxs accepts a slice of transactions and persists then inside the database.
 // An error is returned if the write fails.
 func (w Worker) ExportTxs(txs []*types.Tx) error {
-	// handle all transactions inside the block
+	var wg sync.WaitGroup
+
 	for _, tx := range txs {
-		// save the transaction
+		// Save the transaction
 		err := w.saveTx(tx)
 		if err != nil {
 			return fmt.Errorf("error while storing txs: %s", err)
 		}
 
-		// call the tx handlers
-		go w.handleTx(tx)
+		// Handle the transaction concurrently
+		wg.Add(1)
+		go func(tx *types.Tx) {
+			defer wg.Done()
+			w.handleTx(tx)
+		}(tx)
 
-		// handle all messages contained inside the transaction
+		// Parse all the messages contained inside the transaction
 		sdkMsgs := make([]sdk.Msg, len(tx.Body.Messages))
 		for i, msg := range tx.Body.Messages {
 			var stdMsg sdk.Msg
@@ -349,12 +355,19 @@ func (w Worker) ExportTxs(txs []*types.Tx) error {
 			sdkMsgs[i] = stdMsg
 		}
 
-		// call the msg handlers
+		// Handle all the messages concurrently
 		for i, sdkMsg := range sdkMsgs {
-			go w.handleMessage(i, sdkMsg, tx)
+			wg.Add(1)
+			go func(i int, sdkMsg sdk.Msg) {
+				defer wg.Done()
+				w.handleMessage(i, sdkMsg, tx)
+			}(i, sdkMsg)
 		}
 	}
 
+	// Wait all transactions and messages to be parsed
+	wg.Wait()
+
 	totalBlocks := w.db.GetTotalBlocks()
 	logging.DbBlockCount.WithLabelValues("total_blocks_in_db").Set(float64(totalBlocks))