Ensure that introspection types don't race during initialization. (#469)

* Ensure that introspection types don't race during initialization.

* Ensure tests run on Go1.8+

definition.go

@@ -399,6 +399,13 @@ func NewObject(config ObjectConfig) *Object {
 
 	return objectType
 }
+
+// ensureCache ensures that both fields and interfaces have been initialized properly,
+// to prevent races.
+func (gt *Object) ensureCache() {
+	gt.Fields()
+	gt.Interfaces()
+}
 func (gt *Object) AddFieldConfig(fieldName string, fieldConfig *Field) {
 	if fieldName == "" || fieldConfig == nil {
 		return

introspection.go

@@ -611,6 +611,13 @@ func init() {
 		Type: TypeType,
 	})
 
+	SchemaType.ensureCache()
+	DirectiveType.ensureCache()
+	TypeType.ensureCache()
+	FieldType.ensureCache()
+	InputValueType.ensureCache()
+	EnumValueType.ensureCache()
+
 	// Note that these are FieldDefinition and not FieldConfig,
 	// so the format for args is different.
 	SchemaMetaFieldDef = &FieldDefinition{

race_test.go

@@ -0,0 +1,64 @@
+package graphql_test
+
+import (
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+func TestRace(t *testing.T) {
+	tempdir, err := ioutil.TempDir("", "race")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tempdir)
+
+	filename := filepath.Join(tempdir, "example.go")
+	err = ioutil.WriteFile(filename, []byte(`
+		package main
+
+		import (
+			"runtime"
+			"sync"
+
+			"github.com/graphql-go/graphql"
+		)
+
+		func main() {
+			var wg sync.WaitGroup
+			wg.Add(2)
+			for i := 0; i < 2; i++ {
+				go func() {
+					defer wg.Done()
+					schema, _ := graphql.NewSchema(graphql.SchemaConfig{
+						Query: graphql.NewObject(graphql.ObjectConfig{
+							Name: "RootQuery",
+							Fields: graphql.Fields{
+								"hello": &graphql.Field{
+									Type: graphql.String,
+									Resolve: func(p graphql.ResolveParams) (interface{}, error) {
+										return "world", nil
+									},
+								},
+							},
+						}),
+					})
+					runtime.KeepAlive(schema)
+				}()
+			}
+
+			wg.Wait()
+		} 
+	`), 0755)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	result, err := exec.Command("go", "run", "-race", filename).CombinedOutput()
+	if err != nil || len(result) != 0 {
+		t.Log(string(result))
+		t.Fatal(err)
+	}
+}