Additional connections reuse.

If ngx_drain_connections() fails to immediately reuse any connections
and there are no free connections, it now additionally tries to reuse
a connection again.  This helps to provide at least one free connection
in case of HTTP/2 with lingering close, where merely trying to reuse
a connection once does not free it, but makes it reusable again,
waiting for lingering close.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/core/ngx_connection.c b/src/core/ngx_connection.c
index c082d0dac..8339e2bb7 100644
--- a/src/core/ngx_connection.c
+++ b/src/core/ngx_connection.c
@@ -1310,6 +1310,7 @@ ngx_drain_connections(ngx_cycle_t *cycle)
                       cycle->connection_n);
     }
 
+    c = NULL;
     n = ngx_max(ngx_min(32, cycle->reusable_connections_n / 8), 1);
 
     for (i = 0; i < n; i++) {
@@ -1326,6 +1327,21 @@ ngx_drain_connections(ngx_cycle_t *cycle)
         c->close = 1;
         c->read->handler(c->read);
     }
+
+    if (cycle->free_connection_n == 0 && c && c->reusable) {
+
+        /*
+         * if no connections were freed, try to reuse the last
+         * connection again: this should free it as long as
+         * previous reuse moved it to lingering close
+         */
+
+        ngx_log_debug0(NGX_LOG_DEBUG_CORE, c->log, 0,
+                       "reusing connection again");
+
+        c->close = 1;
+        c->read->handler(c->read);
+    }
 }