Status: introduced the "ngx_stat_waiting" counter.

And corresponding variable $connections_waiting was added.

Previously, waiting connections were counted as the difference between
active connections and the sum of reading and writing connections.
That made it impossible to count more than one request in one connection
as reading or writing (as is the case for SPDY).

Also, we no longer count connections in handshake state as waiting.

src/core/ngx_connection.c

@@ -970,6 +970,10 @@ ngx_reusable_connection(ngx_connection_t *c, ngx_uint_t reusable)
 
     if (c->reusable) {
         ngx_queue_remove(&c->queue);
+
+#if (NGX_STAT_STUB)
+        (void) ngx_atomic_fetch_add(ngx_stat_waiting, -1);
+#endif
     }
 
     c->reusable = reusable;
@@ -979,6 +983,10 @@ ngx_reusable_connection(ngx_connection_t *c, ngx_uint_t reusable)
 
         ngx_queue_insert_head(
             (ngx_queue_t *) &ngx_cycle->reusable_connections_queue, &c->queue);
+
+#if (NGX_STAT_STUB)
+        (void) ngx_atomic_fetch_add(ngx_stat_waiting, 1);
+#endif
     }
 }
 

src/event/ngx_event.c

@@ -73,6 +73,8 @@ ngx_atomic_t   ngx_stat_reading0;
 ngx_atomic_t  *ngx_stat_reading = &ngx_stat_reading0;
 ngx_atomic_t   ngx_stat_writing0;
 ngx_atomic_t  *ngx_stat_writing = &ngx_stat_writing0;
+ngx_atomic_t   ngx_stat_waiting0;
+ngx_atomic_t  *ngx_stat_waiting = &ngx_stat_waiting0;
 
 #endif
 
@@ -511,7 +513,8 @@ ngx_event_module_init(ngx_cycle_t *cycle)
            + cl          /* ngx_stat_requests */
            + cl          /* ngx_stat_active */
            + cl          /* ngx_stat_reading */
-           + cl;         /* ngx_stat_writing */
+           + cl          /* ngx_stat_writing */
+           + cl;         /* ngx_stat_waiting */
 
 #endif
 
@@ -558,6 +561,7 @@ ngx_event_module_init(ngx_cycle_t *cycle)
     ngx_stat_active = (ngx_atomic_t *) (shared + 6 * cl);
     ngx_stat_reading = (ngx_atomic_t *) (shared + 7 * cl);
     ngx_stat_writing = (ngx_atomic_t *) (shared + 8 * cl);
+    ngx_stat_waiting = (ngx_atomic_t *) (shared + 9 * cl);
 
 #endif
 

src/event/ngx_event.h

@@ -511,6 +511,7 @@ extern ngx_atomic_t  *ngx_stat_requests;
 extern ngx_atomic_t  *ngx_stat_active;
 extern ngx_atomic_t  *ngx_stat_reading;
 extern ngx_atomic_t  *ngx_stat_writing;
+extern ngx_atomic_t  *ngx_stat_waiting;
 
 #endif
 

src/http/modules/ngx_http_stub_status_module.c

@@ -73,6 +73,9 @@ static ngx_http_variable_t  ngx_http_stub_status_vars[] = {
     { ngx_string("connections_writing"), NULL, ngx_http_stub_status_variable,
       2, NGX_HTTP_VAR_NOCACHEABLE, 0 },
 
+    { ngx_string("connections_waiting"), NULL, ngx_http_stub_status_variable,
+      3, NGX_HTTP_VAR_NOCACHEABLE, 0 },
+
     { ngx_null_string, NULL, NULL, 0, 0, 0 }
 };
 
@@ -83,7 +86,7 @@ static ngx_int_t ngx_http_status_handler(ngx_http_request_t *r)
     ngx_int_t          rc;
     ngx_buf_t         *b;
     ngx_chain_t        out;
-    ngx_atomic_int_t   ap, hn, ac, rq, rd, wr;
+    ngx_atomic_int_t   ap, hn, ac, rq, rd, wr, wa;
 
     if (r->method != NGX_HTTP_GET && r->method != NGX_HTTP_HEAD) {
         return NGX_HTTP_NOT_ALLOWED;
@@ -126,6 +129,7 @@ static ngx_int_t ngx_http_status_handler(ngx_http_request_t *r)
     rq = *ngx_stat_requests;
     rd = *ngx_stat_reading;
     wr = *ngx_stat_writing;
+    wa = *ngx_stat_waiting;
 
     b->last = ngx_sprintf(b->last, "Active connections: %uA \n", ac);
 
@@ -135,7 +139,7 @@ static ngx_int_t ngx_http_status_handler(ngx_http_request_t *r)
     b->last = ngx_sprintf(b->last, " %uA %uA %uA \n", ap, hn, rq);
 
     b->last = ngx_sprintf(b->last, "Reading: %uA Writing: %uA Waiting: %uA \n",
-                          rd, wr, ac - (rd + wr));
+                          rd, wr, wa);
 
     r->headers_out.status = NGX_HTTP_OK;
     r->headers_out.content_length_n = b->last - b->pos;
@@ -177,6 +181,10 @@ ngx_http_stub_status_variable(ngx_http_request_t *r,
         value = *ngx_stat_writing;
         break;
 
+    case 3:
+        value = *ngx_stat_waiting;
+        break;
+
     /* suppress warning */
     default:
         value = 0;