scylla: conn picker int32 overflow fix

Fixes #29

scylla.go

@@ -90,7 +90,7 @@ type scyllaConnPicker struct {
 	nrConns     int
 	nrShards    int
 	msbIgnore   uint64
-	pos         int32
+	pos         uint64
 }
 
 func newScyllaConnPicker(conn *Conn) *scyllaConnPicker {
@@ -231,7 +231,7 @@ func (p *scyllaConnPicker) closeExcessConns() {
 }
 
 func (p *scyllaConnPicker) randomConn() *Conn {
-	idx := int(atomic.AddInt32(&p.pos, 1))
+	idx := int(atomic.AddUint64(&p.pos, 1))
 	for i := 0; i < len(p.conns); i++ {
 		if conn := p.conns[(idx+i)%len(p.conns)]; conn != nil {
 			return conn

scylla_test.go

@@ -1,6 +1,7 @@
 package gocql
 
 import (
+	"math"
 	"runtime"
 	"sync"
 	"testing"
@@ -136,3 +137,50 @@ func TestScyllaConnPickerShardOf(t *testing.T) {
 		}
 	}
 }
+
+func TestScyllaRandomConnPIcker(t *testing.T) {
+	t.Parallel()
+
+	t.Run("max iterations", func(t *testing.T) {
+		s := &scyllaConnPicker{
+			nrShards:  4,
+			msbIgnore: 12,
+			pos: math.MaxUint64,
+			conns: []*Conn{nil, mockConn("1")},
+		}
+
+		if s.Pick(token(nil)) == nil {
+			t.Fatal("expected connection")
+		}
+	})
+
+	t.Run("async access of max iterations", func(t *testing.T) {
+		s := &scyllaConnPicker{
+			nrShards:  4,
+			msbIgnore: 12,
+			pos: math.MaxUint64,
+			conns: []*Conn{nil, mockConn("1")},
+		}
+
+		var wg sync.WaitGroup
+		for i := 0; i < 3; i++ {
+			wg.Add(1)
+			go pickLoop(t, s, 3, &wg)
+		}
+		wg.Wait()
+
+		if s.pos != 8 {
+			t.Fatalf("expected position to be 8 | actual %d", s.pos)
+		}
+	})
+}
+
+func pickLoop(t *testing.T, s *scyllaConnPicker, c int, wg *sync.WaitGroup) {
+	t.Helper()
+	for i := 0; i < c; i++ {
+		if s.Pick(token(nil)) == nil {
+			t.Fatal("expected connection")
+		}
+	}
+	wg.Done()
+}