🐛 refreshable: fix race condition in ToV2 (#381)

Author: glynternet

refreshable/v2.go

@@ -15,6 +15,10 @@ func ToV2[T any](v1 Refreshable) refreshablev2.Refreshable[T] {
 	v1.Subscribe(func(i interface{}) {
 		v2.Update(i.(T))
 	})
+	// If v1 is updated before the subscription above is registered,
+	// the new v1 would have not propagated to v2.
+	// Here we enforce v2 has the latest v1.
+	v2.Update(v1.Current().(T))
 	return v2
 }
 

refreshable/v2_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestToFromV2(t *testing.T) {
@@ -23,3 +24,18 @@ func TestToFromV2(t *testing.T) {
 	assert.Equal(t, v2.Current(), "updated", "v2 missing updated value")
 	assert.Equal(t, v1.Current(), "updated", "v1 missing updated value")
 }
+
+func TestToV2RespectsUpdates(t *testing.T) {
+	for i := 0; i < 10000; i++ {
+		v1 := NewDefaultRefreshable(1)
+		updateCalled := make(chan struct{})
+		go func() {
+			require.NoError(t, v1.Update(2))
+			close(updateCalled)
+		}()
+		v2 := ToV2[int](v1)
+		<-updateCalled
+		assert.Equal(t, 2, v2.Current(),
+			"v2 should always be updated after Update is called")
+	}
+}