Fix data race in account grouping for account based migration

cmd/util/ledger/util/payload_grouping.go

@@ -112,7 +112,7 @@ func GroupPayloadsByAccount(
 	indexes := make([]int, 0, estimatedNumOfAccount)
 	for i := 0; i < len(p); {
 		indexes = append(indexes, i)
-		i = p.FindNextKeyIndex(i)
+		i = p.FindNextKeyIndexUntil(i, len(p))
 	}
 	end = time.Now()
 
@@ -177,17 +177,17 @@ func (s sortablePayloads) Swap(i, j int) {
 	s[i], s[j] = s[j], s[i]
 }
 
-func (s sortablePayloads) FindNextKeyIndex(i int) int {
+func (s sortablePayloads) FindNextKeyIndexUntil(i int, upperBound int) int {
 	low := i
 	step := 1
-	for low+step < len(s) && s.Compare(low+step, i) == 0 {
+	for low+step < upperBound && s.Compare(low+step, i) == 0 {
 		low += step
 		step *= 2
 	}
 
 	high := low + step
-	if high > len(s) {
-		high = len(s)
+	if high > upperBound {
+		high = upperBound
 	}
 
 	for low < high {
@@ -248,13 +248,13 @@ func mergeInto(source, buffer sortablePayloads, i int, mid int, j int) {
 		// More elements in the both partitions to process.
 		if source.Compare(left, right) <= 0 {
 			// Move left partition elements with the same address to buffer.
-			nextLeft := source.FindNextKeyIndex(left)
+			nextLeft := source.FindNextKeyIndexUntil(left, mid)
 			n := copy(buffer[k:], source[left:nextLeft])
 			left = nextLeft
 			k += n
 		} else {
 			// Move right partition elements with the same address to buffer.
-			nextRight := source.FindNextKeyIndex(right)
+			nextRight := source.FindNextKeyIndexUntil(right, j)
 			n := copy(buffer[k:], source[right:nextRight])
 			right = nextRight
 			k += n

cmd/util/ledger/util/payload_grouping_test.go

@@ -29,6 +29,20 @@ func TestGroupPayloadsByAccount(t *testing.T) {
 	require.Greater(t, groups.Len(), 1)
 }
 
+func TestGroupPayloadsByAccountForDataRace(t *testing.T) {
+	log := zerolog.New(zerolog.NewTestWriter(t))
+
+	const accountSize = 4
+	var payloads []*ledger.Payload
+	for i := 0; i < accountSize; i++ {
+		payloads = append(payloads, generateRandomPayloadsWithAddress(generateRandomAddress(), 100_000)...)
+	}
+
+	const nWorkers = 8
+	groups := util.GroupPayloadsByAccount(log, payloads, nWorkers)
+	require.Equal(t, accountSize, groups.Len())
+}
+
 func TestGroupPayloadsByAccountCompareResults(t *testing.T) {
 	log := zerolog.Nop()
 	payloads := generateRandomPayloads(1000000)
@@ -129,6 +143,36 @@ func generateRandomPayloads(n int) []*ledger.Payload {
 	return payloads
 }
 
+func generateRandomPayloadsWithAddress(address string, n int) []*ledger.Payload {
+	const meanPayloadsPerAccount = 100
+	const minPayloadsPerAccount = 1
+
+	payloads := make([]*ledger.Payload, 0, n)
+
+	for i := 0; i < n; {
+
+		registersForAccount := minPayloadsPerAccount + int(rand2.ExpFloat64()*(meanPayloadsPerAccount-minPayloadsPerAccount))
+		if registersForAccount > n-i {
+			registersForAccount = n - i
+		}
+		i += registersForAccount
+
+		accountKey := convert.RegisterIDToLedgerKey(flow.RegisterID{
+			Owner: address,
+			Key:   generateRandomString(10),
+		})
+		for j := 0; j < registersForAccount; j++ {
+			payloads = append(payloads,
+				ledger.NewPayload(
+					accountKey,
+					[]byte(generateRandomString(10)),
+				))
+		}
+	}
+
+	return payloads
+}
+
 func generateRandomAccountKey() ledger.Key {
 	return convert.RegisterIDToLedgerKey(flow.RegisterID{
 		Owner: generateRandomAddress(),