Revert "Ensure OnStart/OnStop hooks can only be called once (uber-go#931

)" (uber-go#946)

This reverts commit 5566339.

app.go

@@ -300,10 +300,6 @@ type App struct {
 	dones       []chan os.Signal
 	shutdownSig os.Signal
 
-	// Used to make sure Start/Stop is called only once.
-	runStart sync.Once
-	runStop  sync.Once
-
 	osExit func(code int) // os.Exit override; used for testing only
 }
 
@@ -665,25 +661,21 @@ var (
 // Note that Start short-circuits immediately if the New constructor
 // encountered any errors in application initialization.
 func (app *App) Start(ctx context.Context) (err error) {
-	app.runStart.Do(func() {
-		defer func() {
-			app.log.LogEvent(&fxevent.Started{Err: err})
-		}()
+	defer func() {
+		app.log.LogEvent(&fxevent.Started{Err: err})
+	}()
 
-		if app.err != nil {
-			// Some provides failed, short-circuit immediately.
-			err = app.err
-			return
-		}
+	if app.err != nil {
+		// Some provides failed, short-circuit immediately.
+		return app.err
+	}
 
-		err = withTimeout(ctx, &withTimeoutParams{
-			hook:      _onStartHook,
-			callback:  app.start,
-			lifecycle: app.lifecycle,
-			log:       app.log,
-		})
+	return withTimeout(ctx, &withTimeoutParams{
+		hook:      _onStartHook,
+		callback:  app.start,
+		lifecycle: app.lifecycle,
+		log:       app.log,
 	})
-	return
 }
 
 func (app *App) start(ctx context.Context) error {
@@ -711,20 +703,16 @@ func (app *App) start(ctx context.Context) error {
 // called are executed. However, all those hooks are executed, even if some
 // fail.
 func (app *App) Stop(ctx context.Context) (err error) {
-	app.runStop.Do(func() {
-		// Protect the Stop hooks from being called multiple times.
-		defer func() {
-			app.log.LogEvent(&fxevent.Stopped{Err: err})
-		}()
+	defer func() {
+		app.log.LogEvent(&fxevent.Stopped{Err: err})
+	}()
 
-		err = withTimeout(ctx, &withTimeoutParams{
-			hook:      _onStopHook,
-			callback:  app.lifecycle.Stop,
-			lifecycle: app.lifecycle,
-			log:       app.log,
-		})
+	return withTimeout(ctx, &withTimeoutParams{
+		hook:      _onStopHook,
+		callback:  app.lifecycle.Stop,
+		lifecycle: app.lifecycle,
+		log:       app.log,
 	})
-	return
 }
 
 // Done returns a channel of signals to block on after starting the

app_test.go

@@ -31,7 +31,6 @@ import (
 	"reflect"
 	"runtime"
 	"strings"
-	"sync"
 	"testing"
 	"time"
 
@@ -1282,47 +1281,6 @@ func TestAppStart(t *testing.T) {
 		err := app.Start(context.Background()).Error()
 		assert.Contains(t, err, "OnStart hook added by go.uber.org/fx_test.TestAppStart.func10.1 failed: goroutine exited without returning")
 	})
-
-	t.Run("Start/Stop should be called exactly once only.", func(t *testing.T) {
-		t.Parallel()
-		startCalled := 0
-		stopCalled := 0
-		app := fxtest.New(t,
-			Provide(Annotate(func() int { return 0 },
-				OnStart(func(context.Context) error {
-					startCalled += 1
-					return nil
-				}),
-				OnStop(func(context.Context) error {
-					stopCalled += 1
-					return nil
-				})),
-			),
-			Invoke(func(i int) {
-				assert.Equal(t, 0, i)
-			}),
-		)
-		var wg sync.WaitGroup
-		for i := 0; i < 10; i++ {
-			wg.Add(1)
-			go func() {
-				defer wg.Done()
-				app.Start(context.Background())
-			}()
-		}
-		wg.Wait()
-		assert.Equal(t, 1, startCalled)
-		for i := 0; i < 10; i++ {
-			wg.Add(1)
-			go func() {
-				defer wg.Done()
-				app.Stop(context.Background())
-			}()
-		}
-		wg.Wait()
-		assert.Equal(t, 1, stopCalled)
-	})
-
 }
 
 func TestAppStop(t *testing.T) {