synchronized with lua-nginx-module #f64ec8c.

bugfix: tcpsock:setkeepalive: worker processes might take too long to
gracefully shut down when the keep alive connections take a long max
idle time.

Now we avoid putting any new connections into the pool when nginx is
already shutting down.

Thanks Dejiang Zhu for the upstream patch.

Author: thibaultcha

src/subsys/ngx_subsys_lua_socket_tcp.c.tt2

@@ -5266,6 +5266,14 @@ ngx_[% subsys %]_lua_socket_tcp_setkeepalive(lua_State *L)
         return 2;
     }
 
+    if (ngx_terminate || ngx_exiting) {
+        ngx_log_debug1(NGX_LOG_DEBUG_[% SUBSYS %], pc->log, 0,
+                       "[% log_prefix %]lua tcp socket set keepalive while "
+                       "process exiting, closing connection %p", c);
+
+        goto finalize;
+    }
+
     ngx_log_debug1(NGX_LOG_DEBUG_[% SUBSYS %], pc->log, 0,
                    "[% log_prefix %]lua tcp socket set keepalive: saving "
                    "connection %p", c);
@@ -5435,6 +5443,8 @@ ngx_[% subsys %]_lua_socket_tcp_setkeepalive(lua_State *L)
         }
     }
 
+finalize:
+
 #if 1
     ngx_[% subsys %]_lua_socket_tcp_finalize(r, u);
 #endif