fix: pop entries from each drives in parallel (#9918)

cmd/xl-zones.go

@@ -859,9 +859,18 @@ func (z *xlZones) listObjects(ctx context.Context, bucket, prefix, marker, delim
 // N times until this boolean is 'false'.
 func lexicallySortedEntryZone(zoneEntryChs [][]FileInfoCh, zoneEntries [][]FileInfo, zoneEntriesValid [][]bool) (FileInfo, int, int, bool) {
 	for i, entryChs := range zoneEntryChs {
+		i := i
+		var wg sync.WaitGroup
 		for j := range entryChs {
-			zoneEntries[i][j], zoneEntriesValid[i][j] = entryChs[j].Pop()
+			j := j
+			wg.Add(1)
+			// Pop() entries in parallel for large drive setups.
+			go func() {
+				defer wg.Done()
+				zoneEntries[i][j], zoneEntriesValid[i][j] = entryChs[j].Pop()
+			}()
 		}
+		wg.Wait()
 	}
 
 	var isTruncated = false
@@ -961,9 +970,18 @@ func mergeZonesEntriesCh(zonesEntryChs [][]FileInfoCh, maxKeys int, ndisks int)
 
 func isTruncatedZones(zoneEntryChs [][]FileInfoCh, zoneEntries [][]FileInfo, zoneEntriesValid [][]bool) bool {
 	for i, entryChs := range zoneEntryChs {
+		i := i
+		var wg sync.WaitGroup
 		for j := range entryChs {
-			zoneEntries[i][j], zoneEntriesValid[i][j] = entryChs[j].Pop()
+			j := j
+			wg.Add(1)
+			// Pop() entries in parallel for large drive setups.
+			go func() {
+				defer wg.Done()
+				zoneEntries[i][j], zoneEntriesValid[i][j] = entryChs[j].Pop()
+			}()
 		}
+		wg.Wait()
 	}
 
 	var isTruncated = false