Remove the check for unique project ID within the process (#9)

Fixes: #8

Author: Ramon Nogueira

stats.go

@@ -65,16 +65,8 @@ type statsExporter struct {
 	defaultLabels map[string]labelValue
 }
 
-// Enforces the singleton on NewExporter per projectID per process
-// lest there will be races with Stackdriver.
 var (
-	seenProjectsMu sync.Mutex
-	seenProjects   = make(map[string]bool)
-)
-
-var (
-	errBlankProjectID    = errors.New("expecting a non-blank ProjectID")
-	errSingletonExporter = errors.New("only one exporter can be created per unique ProjectID per process")
+	errBlankProjectID = errors.New("expecting a non-blank ProjectID")
 )
 
 // newStatsExporter returns an exporter that uploads stats data to Stackdriver Monitoring.
@@ -85,18 +77,6 @@ func newStatsExporter(o Options, enforceProjectUniqueness bool) (*statsExporter,
 		return nil, errBlankProjectID
 	}
 
-	if enforceProjectUniqueness {
-		seenProjectsMu.Lock()
-		_, seen := seenProjects[o.ProjectID]
-		if !seen {
-			seenProjects[o.ProjectID] = true
-		}
-		seenProjectsMu.Unlock()
-		if seen {
-			return nil, errSingletonExporter
-		}
-	}
-
 	opts := append(o.MonitoringClientOptions, option.WithUserAgent(userAgent))
 	client, err := monitoring.NewMetricClient(context.Background(), opts...)
 	if err != nil {

stats_test.go

@@ -48,28 +48,6 @@ func TestRejectBlankProjectID(t *testing.T) {
 	}
 }
 
-// Ensure only one exporter per projectID per process, any
-// subsequent invocations of NewExporter should fail.
-func TestNewExporterSingletonPerProcess(t *testing.T) {
-	ids := []string{"open-census.io", "x", "fakeProjectID"}
-	for _, projectID := range ids {
-		opts := Options{ProjectID: projectID, MonitoringClientOptions: authOptions}
-		exp, err := newStatsExporter(opts, true)
-		if err != nil {
-			t.Errorf("NewExporter() projectID = %q err = %q", projectID, err)
-			continue
-		}
-		if exp == nil {
-			t.Errorf("NewExporter returned a nil Exporter")
-			continue
-		}
-		exp, err = newStatsExporter(opts, true)
-		if err == nil || exp != nil {
-			t.Errorf("NewExporter more than once should fail; exp (%v) err %v", exp, err)
-		}
-	}
-}
-
 func TestExporter_makeReq(t *testing.T) {
 	m := stats.Float64("test-measure", "measure desc", "unit")