Proper signal handling in monitor process

cmd/syncthing/monitor.go

@@ -9,9 +9,11 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"os/signal"
 	"path/filepath"
 	"strings"
 	"sync"
+	"syscall"
 	"time"
 )
 
@@ -33,6 +35,10 @@ func monitorMain() {
 	args := os.Args
 	var restarts [countRestarts]time.Time
 
+	sign := make(chan os.Signal, 1)
+	sigTerm := syscall.Signal(0xf)
+	signal.Notify(sign, os.Interrupt, sigTerm, os.Kill)
+
 	for {
 		if t := time.Since(restarts[0]); t < loopThreshold {
 			l.Warnf("%d restarts in %v; not retrying further", countRestarts, t)
@@ -68,10 +74,23 @@ func monitorMain() {
 		go copyStderr(stderr)
 		go copyStdout(stdout)
 
-		err = cmd.Wait()
-		if err == nil {
-			// Successfull exit indicates an intentional shutdown
+		exit := make(chan error)
+
+		go func() {
+			exit <- cmd.Wait()
+		}()
+
+		select {
+		case s := <-sign:
+			l.Infof("Signal %d received; exiting", s)
+			cmd.Process.Kill()
+			<-exit
 			return
+		case <-exit:
+			if err == nil {
+				// Successfull exit indicates an intentional shutdown
+				return
+			}
 		}
 
 		l.Infoln("Syncthing exited:", err)