Assignment to the variable rrp->peers->last_cached cannot be found in anywhere in total nginx-1.3.5 source code, if the variable's default value is zero, this conditional will never be true:

ngx_int_t
ngx_http_upstream_get_round_robin_peer(ngx_peer_connection_t *pc, void *data)
{
ngx_http_upstream_rr_peer_data_t *rrp = data;
...
if (rrp->peers->last_cached) { ==============>//never be true?

/* cached connection */

c = rrp->peers->cached[rrp->peers->last_cached];
rrp->peers->last_cached--;

/* ngx_unlock_mutex(ppr->peers->mutex); */

#if (NGX_THREADS)
c->read->lock = c->read->own_lock;
c->write->lock = c->write->own_lock;
#endif

pc->connection = c;
pc->cached = 1;

return NGX_OK;
}
...

i don't know if i am missing something or not, can anyone help me understand this? Thank you in advance.