# HG changeset patch
# User Roman Arutyunyan <arut@nginx.com>
# Date 1491238449 -10800
#      Mon Apr 03 19:54:09 2017 +0300
# Node ID 629cb53e0ad84337c933599edc50d38b2ddf5c12
# Parent  3ff293cfdab85082a9560ab56ea9f16b02a8a8c8
Background subrequests for cache updates.

Previously, cache background update might not work as expected, making client
wait for it to complete before receiving the final part of stale response.
This could happen if the response could not be sent to the client socket in one
filter chain call.

Now background cache update is done in a background subrequest.  This type of
subrequest does not block any other subrequests or the main request.

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -2516,6 +2516,7 @@ ngx_http_subrequest(ngx_http_request_t *
 
     sr->subrequest_in_memory = (flags & NGX_HTTP_SUBREQUEST_IN_MEMORY) != 0;
     sr->waited = (flags & NGX_HTTP_SUBREQUEST_WAITED) != 0;
+    sr->background = (flags & NGX_HTTP_SUBREQUEST_BACKGROUND) != 0;
 
     sr->unparsed_uri = r->unparsed_uri;
     sr->method_name = ngx_http_core_get_method;
@@ -2529,29 +2530,31 @@ ngx_http_subrequest(ngx_http_request_t *
     sr->read_event_handler = ngx_http_request_empty_handler;
     sr->write_event_handler = ngx_http_handler;
 
-    if (c->data == r && r->postponed == NULL) {
-        c->data = sr;
-    }
-
     sr->variables = r->variables;
 
     sr->log_handler = r->log_handler;
 
-    pr = ngx_palloc(r->pool, sizeof(ngx_http_postponed_request_t));
-    if (pr == NULL) {
-        return NGX_ERROR;
-    }
-
-    pr->request = sr;
-    pr->out = NULL;
-    pr->next = NULL;
-
-    if (r->postponed) {
-        for (p = r->postponed; p->next; p = p->next) { /* void */ }
-        p->next = pr;
-
-    } else {
-        r->postponed = pr;
+    if (!sr->background) {
+        if (c->data == r && r->postponed == NULL) {
+            c->data = sr;
+        }
+
+        pr = ngx_palloc(r->pool, sizeof(ngx_http_postponed_request_t));
+        if (pr == NULL) {
+            return NGX_ERROR;
+        }
+
+        pr->request = sr;
+        pr->out = NULL;
+        pr->next = NULL;
+
+        if (r->postponed) {
+            for (p = r->postponed; p->next; p = p->next) { /* void */ }
+            p->next = pr;
+
+        } else {
+            r->postponed = pr;
+        }
     }
 
     sr->internal = 1;
diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -2347,6 +2347,26 @@ ngx_http_finalize_request(ngx_http_reque
     }
 
     if (r != r->main) {
+        clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+
+        if (r->background) {
+            if (!r->logged) {
+                if (clcf->log_subrequest) {
+                    ngx_http_log_request(r);
+                }
+
+                r->logged = 1;
+
+            } else {
+                ngx_log_error(NGX_LOG_ALERT, c->log, 0,
+                              "subrequest: \"%V?%V\" logged again",
+                              &r->uri, &r->args);
+            }
+
+            r->done = 1;
+            ngx_http_finalize_connection(r);
+            return;
+        }
 
         if (r->buffered || r->postponed) {
 
@@ -2364,9 +2384,6 @@ ngx_http_finalize_request(ngx_http_reque
             r->main->count--;
 
             if (!r->logged) {
-
-                clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
-
                 if (clcf->log_subrequest) {
                     ngx_http_log_request(r);
                 }
@@ -2430,6 +2447,8 @@ ngx_http_finalize_request(ngx_http_reque
     }
 
     r->done = 1;
+
+    r->read_event_handler = ngx_http_block_reading;
     r->write_event_handler = ngx_http_request_empty_handler;
 
     if (!r->post_action) {
@@ -2548,6 +2567,8 @@ ngx_http_finalize_connection(ngx_http_re
         return;
     }
 
+    r = r->main;
+
     if (r->reading_body) {
         r->keepalive = 0;
         r->lingering_close = 1;
diff --git a/src/http/ngx_http_request.h b/src/http/ngx_http_request.h
--- a/src/http/ngx_http_request.h
+++ b/src/http/ngx_http_request.h
@@ -63,6 +63,7 @@
 #define NGX_HTTP_SUBREQUEST_IN_MEMORY      2
 #define NGX_HTTP_SUBREQUEST_WAITED         4
 #define NGX_HTTP_SUBREQUEST_CLONE          8
+#define NGX_HTTP_SUBREQUEST_BACKGROUND     16
 
 #define NGX_HTTP_LOG_UNSAFE                1
 
@@ -482,7 +483,6 @@ struct ngx_http_request_s {
 
 #if (NGX_HTTP_CACHE)
     unsigned                          cached:1;
-    unsigned                          cache_updater:1;
 #endif
 
 #if (NGX_HTTP_GZIP)
@@ -539,6 +539,7 @@ struct ngx_http_request_s {
     unsigned                          stat_writing:1;
     unsigned                          stat_processing:1;
 
+    unsigned                          background:1;
     unsigned                          health_check:1;
 
     /* used to parse HTTP headers */
diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -878,7 +878,7 @@ ngx_http_upstream_cache(ngx_http_request
     case NGX_HTTP_CACHE_STALE:
 
         if (((u->conf->cache_use_stale & NGX_HTTP_UPSTREAM_FT_UPDATING)
-             || c->stale_updating) && !r->cache_updater
+             || c->stale_updating) && !r->background
             && u->conf->cache_background_update)
         {
             r->cache->background = 1;
@@ -891,7 +891,7 @@ ngx_http_upstream_cache(ngx_http_request
     case NGX_HTTP_CACHE_UPDATING:
 
         if (((u->conf->cache_use_stale & NGX_HTTP_UPSTREAM_FT_UPDATING)
-             || c->stale_updating) && !r->cache_updater)
+             || c->stale_updating) && !r->background)
         {
             u->cache_status = rc;
             rc = NGX_OK;
@@ -1075,14 +1075,14 @@ ngx_http_upstream_cache_background_updat
     }
 
     if (ngx_http_subrequest(r, &r->uri, &r->args, &sr, NULL,
-                            NGX_HTTP_SUBREQUEST_CLONE)
+                            NGX_HTTP_SUBREQUEST_CLONE
+                            |NGX_HTTP_SUBREQUEST_BACKGROUND)
         != NGX_OK)
     {
         return NGX_ERROR;
     }
 
     sr->header_only = 1;
-    sr->cache_updater = 1;
 
     return NGX_OK;
 }