shutdown: introduce the new NotifyContext

As of Go 1.16 signal.NotifyContext ties the context to
the signal handling instead of having to do it manually.
This PR also bumps the Go version.

Signed-off-by: crozzy <joseph.crosland@gmail.com>

.github/workflows/cut-release.yml

@@ -53,7 +53,7 @@ jobs:
   release-binaries:
     name: Create Release Binaries
     runs-on: 'ubuntu-latest'
-    container: quay.io/projectquay/golang:1.15
+    container: quay.io/projectquay/golang:1.16
     needs: release-archive
     strategy:
       matrix:

cmd/clair/main.go

@@ -117,44 +117,26 @@ func main() {
 	})
 
 	// Signal handler goroutine.
-	srvs.Go(func() error {
-		c := make(chan os.Signal, 1)
-		signal.Notify(c, os.Interrupt)
+	go func() {
+		ctx, stop := signal.NotifyContext(ctx, os.Interrupt)
 		defer func() {
-			signal.Stop(c)
-			close(c)
-			zlog.Info(ctx).Msg("unregistered signal handler")
-		}()
-		zlog.Info(ctx).Msg("registered signal handler")
-		select {
-		case sig := <-c:
-			zlog.Info(ctx).
-				Stringer("signal", sig).
-				Msg("gracefully shutting down")
-			// Note that we're using the root context here, so that we get a
-			// full timeout if one errgroup goroutine returns uncleanly.
-			tctx, done := context.WithTimeout(ctx, 10*time.Second)
+			// Note that we're using a background context here, so that we get a
+			// full timeout if the signal handler has fired.
+			tctx, done := context.WithTimeout(context.Background(), 10*time.Second)
 			err := down.Shutdown(tctx)
-			done()
 			if err != nil {
 				zlog.Error(ctx).Err(err).Msg("error shutting down server")
 			}
+			done()
+			stop()
+			zlog.Info(ctx).Msg("unregistered signal handler")
+		}()
+		zlog.Info(ctx).Msg("registered signal handler")
+		select {
+		case <-ctx.Done():
+			zlog.Info(ctx).Stringer("signal", os.Interrupt).Msg("gracefully shutting down")
 		case <-srvctx.Done():
 		}
-		return nil
-	})
-	// Spawn a goroutine outside to wait on the errgroup.
-	//
-	// This is needed to call shutdown and cause the servers to return when only
-	// one has returned an error.
-	go func() {
-		<-srvctx.Done()
-		tctx, done := context.WithTimeout(ctx, 10*time.Second)
-		err := down.Shutdown(tctx)
-		done()
-		if err != nil {
-			zlog.Error(ctx).Err(err).Msg("error shutting down server")
-		}
 	}()
 
 	zlog.Info(ctx).Str("version", Version).Msg("ready")