fix systemd restart waiting due to signal handling

std/signal.go

@@ -28,16 +28,23 @@ import (
 	"log"
 	"os"
 	"os/signal"
+	"sync"
 	"syscall"
+	"time"
 
 	kcp "github.com/xtaci/kcp-go/v5"
 )
 
+const (
+	EXIT_WAIT = 5 // max seconds to wait before exit
+)
+
 func init() {
 	go sigHandler()
 }
 
 func sigHandler() {
+	var exitOnce sync.Once
 	ch := make(chan os.Signal, 1)
 	signal.Notify(ch, syscall.SIGUSR1, syscall.SIGTERM, syscall.SIGINT)
 	signal.Ignore(syscall.SIGPIPE)
@@ -51,6 +58,14 @@ func sigHandler() {
 			postProcess()
 			signal.Stop(ch)
 			syscall.Kill(syscall.Getpid(), syscall.SIGTERM)
+
+			// wait for max EXIT_WAIT seconds before exit
+			exitOnce.Do(func() {
+				go func() {
+					<-time.After(EXIT_WAIT * time.Second)
+					os.Exit(0)
+				}()
+			})
 		}
 	}
 }