[nginx] Reuse of connections in lingering close.

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/3e83336cda5b
branches:  
changeset: 7766:3e83336cda5b
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Thu Feb 11 21:52:09 2021 +0300
description:
Reuse of connections in lingering close.

This is particularly important in HTTP/2, where keepalive connections
are closed with lingering.  Before the patch, reusing a keepalive HTTP/2
connection resulted in the connection waiting for lingering close to
remain in the reusable connections queue, preventing ngx_drain_connections()
from closing additional connections.

The patch fixes it by marking the connection reusable again, and so
moving it in the reusable connections queue.  Further, it makes actually
possible to reuse such connections if needed.

diffstat:

 src/http/ngx_http_request.c |  5 ++++-
 src/http/v2/ngx_http_v2.c   |  5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diffs (44 lines):

diff -r 519b55453c45 -r 3e83336cda5b src/http/ngx_http_request.c
--- a/src/http/ngx_http_request.c	Mon Feb 01 16:42:50 2021 +0300
+++ b/src/http/ngx_http_request.c	Thu Feb 11 21:52:09 2021 +0300
@@ -3437,6 +3437,9 @@ ngx_http_set_lingering_close(ngx_connect
         return;
     }
 
+    c->close = 0;
+    ngx_reusable_connection(c, 1);
+
     ngx_add_timer(rev, clcf->lingering_timeout);
 
     if (rev->ready) {
@@ -3461,7 +3464,7 @@ ngx_http_lingering_close_handler(ngx_eve
     ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
                    "http lingering close handler");
 
-    if (rev->timedout) {
+    if (rev->timedout || c->close) {
         ngx_http_close_request(r, 0);
         return;
     }
diff -r 519b55453c45 -r 3e83336cda5b src/http/v2/ngx_http_v2.c
--- a/src/http/v2/ngx_http_v2.c	Mon Feb 01 16:42:50 2021 +0300
+++ b/src/http/v2/ngx_http_v2.c	Thu Feb 11 21:52:09 2021 +0300
@@ -767,6 +767,9 @@ ngx_http_v2_lingering_close(ngx_connecti
         return;
     }
 
+    c->close = 0;
+    ngx_reusable_connection(c, 1);
+
     ngx_add_timer(rev, clcf->lingering_timeout);
 
     if (rev->ready) {
@@ -791,7 +794,7 @@ ngx_http_v2_lingering_close_handler(ngx_
     ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
                    "http2 lingering close handler");
 
-    if (rev->timedout) {
+    if (rev->timedout || c->close) {
         ngx_http_close_connection(c);
         return;
     }