Core: idle connections now closed only once on exiting.

Iterating through all connections takes a lot of CPU time, especially
with large number of worker connections configured.  As a result
nginx processes used to consume CPU time during graceful shutdown.
To mitigate this we now only do a full scan for idle connections when
shutdown signal is received.

Transitions of connections to idle ones are now expected to be
avoided if the ngx_exiting flag is set.  The upstream keepalive module
was modified to follow this.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/http/modules/ngx_http_upstream_keepalive_module.c b/src/http/modules/ngx_http_upstream_keepalive_module.c
index 768881ee4..51887b4e8 100644
--- a/src/http/modules/ngx_http_upstream_keepalive_module.c
+++ b/src/http/modules/ngx_http_upstream_keepalive_module.c
@@ -302,6 +302,10 @@ ngx_http_upstream_free_keepalive_peer(ngx_peer_connection_t *pc, void *data,
         goto invalid;
     }
 
+    if (ngx_terminate || ngx_exiting) {
+        goto invalid;
+    }
+
     if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
         goto invalid;
     }