Core: reusing connections in advance.

Reworked connections reuse, so closing connections is attempted in
advance, as long as number of free connections is less than 1/16 of
worker connections configured.  This ensures that new connections can
be handled even if closing a reusable connection requires some time,
for example, for a lingering close (ticket #2017).

The 1/16 ratio is selected to be smaller than 1/8 used for disabling
accept when working with accept mutex, so nginx will try to balance
new connections to different workers first, and will start reusing
connections only if this won't help.

1 files changed, 5 insertions, 6 deletions

diff --git a/src/core/ngx_connection.c b/src/core/ngx_connection.c
index 91e1b3b2e..c082d0dac 100644
--- a/src/core/ngx_connection.c
+++ b/src/core/ngx_connection.c
@@ -1107,12 +1107,9 @@ ngx_get_connection(ngx_socket_t s, ngx_log_t *log)
         return NULL;
     }
 
-    c = ngx_cycle->free_connections;
+    ngx_drain_connections((ngx_cycle_t *) ngx_cycle);
 
-    if (c == NULL) {
-        ngx_drain_connections((ngx_cycle_t *) ngx_cycle);
-        c = ngx_cycle->free_connections;
-    }
+    c = ngx_cycle->free_connections;
 
     if (c == NULL) {
         ngx_log_error(NGX_LOG_ALERT, log, 0,
@@ -1298,7 +1295,9 @@ ngx_drain_connections(ngx_cycle_t *cycle)
     ngx_queue_t       *q;
     ngx_connection_t  *c;
 
-    if (cycle->reusable_connections_n == 0) {
+    if (cycle->free_connection_n > cycle->connection_n / 16
+        || cycle->reusable_connections_n == 0)
+    {
         return;
     }