Forum: NGINX is that possible to queue request one by one

Hi

nginx module limit_req only can limit request frequency by url param 
key.
it delay a request by "ngx_add_timer(r->connection->write, delay)".

my requirement is a little bit different. i need the next request be
process immediately after the prev one have done.
i have tried to use "ngx_http_cleanup_add". but it seem that the
ngx_http_request_t is not in shared mem, i can't use
"ngx_add_timer(r->connection->write, 0)" to notify the next request.

thx