Removed c->single_connection flag.

The c->single_connection was intended to be used as lock mechanism
to serialize modifications of request object from several threads
working with client and upstream connections.  The flag is redundant
since threads in nginx have never been used that way.

src/core/ngx_connection.c

@@ -900,11 +900,9 @@ ngx_close_connection(ngx_connection_t *c)
     c->read->closed = 1;
     c->write->closed = 1;
 
-    if (c->single_connection) {
     ngx_unlock(&c->lock);
     c->read->locked = 0;
     c->write->locked = 0;
-    }
 
     ngx_mutex_unlock(ngx_posted_events_mutex);
 

src/core/ngx_connection.h

@@ -152,7 +152,6 @@ struct ngx_connection_s {
 
     unsigned            log_error:3;     /* ngx_connection_log_error_e */
 
-    unsigned            single_connection:1;
     unsigned            unexpected_eof:1;
     unsigned            timedout:1;
     unsigned            error:1;

src/http/ngx_http_request.c

@@ -554,7 +554,6 @@ ngx_http_init_request(ngx_event_t *rev)
         return;
     }
 
-    c->single_connection = 1;
     c->destroyed = 0;
 
 #if (NGX_HTTP_SSL)

src/http/ngx_http_upstream.c

@@ -1118,8 +1118,6 @@ ngx_http_upstream_connect(ngx_http_request_t *r, ngx_http_upstream_t *u)
 
     r->connection->log->action = "connecting to upstream";
 
-    r->connection->single_connection = 0;
-
     if (u->state && u->state->response_sec) {
         tp = ngx_timeofday();
         u->state->response_sec = tp->sec - u->state->response_sec;