bugfix: nginx would crash when receiving SIGHUP in the single process mode.

Signed-off-by: Yichun Zhang (agentzh) <yichun@openresty.com>

patches/nginx-1.17.8-single_process_graceful_exit.patch

@@ -1,8 +1,30 @@
+diff --git a/src/os/unix/ngx_process.c b/src/os/unix/ngx_process.c
+index 15680237..12a8c687 100644
+--- a/src/os/unix/ngx_process.c
++++ b/src/os/unix/ngx_process.c
+@@ -362,8 +362,15 @@ ngx_signal_handler(int signo, siginfo_t *siginfo, void *ucontext)
+             break;
+ 
+         case ngx_signal_value(NGX_RECONFIGURE_SIGNAL):
+-            ngx_reconfigure = 1;
+-            action = ", reconfiguring";
++            if (ngx_process == NGX_PROCESS_SINGLE) {
++                ngx_terminate = 1;
++                action = ", exiting";
++
++            } else {
++                ngx_reconfigure = 1;
++                action = ", reconfiguring";
++            }
++
+             break;
+ 
+         case ngx_signal_value(NGX_REOPEN_SIGNAL):
 diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
-index 1710ea81..b379da9c 100644
+index 5817a2c2..f3d58e97 100644
 --- a/src/os/unix/ngx_process_cycle.c
 +++ b/src/os/unix/ngx_process_cycle.c
-@@ -304,11 +304,26 @@ ngx_single_process_cycle(ngx_cycle_t *cycle)
+@@ -305,11 +305,26 @@ ngx_single_process_cycle(ngx_cycle_t *cycle)
      }
  
      for ( ;; ) {
@@ -30,7 +52,7 @@ index 1710ea81..b379da9c 100644
  
              for (i = 0; cycle->modules[i]; i++) {
                  if (cycle->modules[i]->exit_process) {
-@@ -319,6 +334,20 @@ ngx_single_process_cycle(ngx_cycle_t *cycle)
+@@ -320,6 +335,20 @@ ngx_single_process_cycle(ngx_cycle_t *cycle)
              ngx_master_process_exit(cycle);
          }