From bf15535a5bf5783b53e6764268dd1554cde3608e Mon Sep 17 00:00:00 2001
From: sanghee <afk.sh94@gmail.com>
Date: Thu, 3 Jan 2019 22:44:32 +0900
Subject: [PATCH] fix panic: sync: negative WaitGroup counter

---
 grace/conn.go   | 3 +--
 grace/server.go | 5 +++++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/grace/conn.go b/grace/conn.go
index e020f850..32623650 100644
--- a/grace/conn.go
+++ b/grace/conn.go
@@ -28,12 +28,11 @@ func (c *graceConn) Close() (err error) {
 	}()
 
 	c.m.Lock()
+	defer c.m.Unlock()
 	if c.closed {
-		c.m.Unlock()
 		return
 	}
 	c.server.wg.Done()
 	c.closed = true
-	c.m.Unlock()
 	return c.Conn.Close()
 }
diff --git a/grace/server.go b/grace/server.go
index 513a52a9..ef5cbe7e 100644
--- a/grace/server.go
+++ b/grace/server.go
@@ -34,6 +34,11 @@ type Server struct {
 // creating a new service goroutine for each.
 // The service goroutines read requests and then call srv.Handler to reply to them.
 func (srv *Server) Serve() (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			log.Println("wait group counter is negative", r)
+		}
+	}()
 	srv.state = StateRunning
 	err = srv.Server.Serve(srv.GraceListener)
 	log.Println(syscall.Getpid(), "Waiting for connections to finish...")