mount: ensure atexit gets run on interrupt

When running `rclone mount`, there were 2 signal handlers for `os.Interrupt`.

Those handlers would run concurrently and in some cases cause either unmount or `atexit.Run()` being skipped.

In addition `atexit.Run()` will get called in `resolveExitCode` to ensure cleanup on errors.

cmd/cmd.go

@@ -471,6 +471,7 @@ func initConfig() {
 }
 
 func resolveExitCode(err error) {
+	atexit.Run()
 	if err == nil {
 		os.Exit(exitCodeSuccess)
 	}

cmd/mount/mount.go

@@ -13,6 +13,7 @@ import (
 	fusefs "bazil.org/fuse/fs"
 	"github.com/ncw/rclone/cmd/mountlib"
 	"github.com/ncw/rclone/fs"
+	"github.com/ncw/rclone/lib/atexit"
 	"github.com/ncw/rclone/vfs"
 	"github.com/ncw/rclone/vfs/vfsflags"
 	"github.com/okzk/sdnotify"
@@ -133,6 +134,7 @@ func Mount(f fs.Fs, mountpoint string) error {
 	signal.Notify(sigInt, syscall.SIGINT, syscall.SIGTERM)
 	sigHup := make(chan os.Signal, 1)
 	signal.Notify(sigHup, syscall.SIGHUP)
+	atexit.IgnoreSignals()
 
 	if err := sdnotify.SdNotifyReady(); err != nil && err != sdnotify.SdNotifyNoSocket {
 		return errors.Wrap(err, "failed to notify systemd")

lib/atexit/atexit.go

@@ -14,6 +14,7 @@ import (
 
 var (
 	fns          []func()
+	exitChan     chan os.Signal
 	exitOnce     sync.Once
 	registerOnce sync.Once
 )
@@ -24,10 +25,13 @@ func Register(fn func()) {
 	// Run AtExit handlers on SIGINT or SIGTERM so everything gets
 	// tidied up properly
 	registerOnce.Do(func() {
+		exitChan = make(chan os.Signal, 1)
+		signal.Notify(exitChan, os.Interrupt) // syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT
 		go func() {
-			ch := make(chan os.Signal, 1)
-			signal.Notify(ch, os.Interrupt) // syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT
-			sig := <-ch
+			sig, closed := <-exitChan
+			if closed {
+				return
+			}
 			fs.Infof(nil, "Signal received: %s", sig)
 			Run()
 			fs.Infof(nil, "Exiting...")
@@ -36,6 +40,16 @@ func Register(fn func()) {
 	})
 }
 
+// IgnoreSignals disables the signal handler and prevents Run from beeing executed automatically
+func IgnoreSignals() {
+	registerOnce.Do(func() {})
+	if exitChan != nil {
+		signal.Stop(exitChan)
+		close(exitChan)
+		exitChan = nil
+	}
+}
+
 // Run all the at exit functions if they haven't been run already
 func Run() {
 	exitOnce.Do(func() {