http Keepalive implementation

[prkumar]

I was going through NGINX source code to implement keepalive for nginx
zeromq plugin that I have developed.
I have been inspired by ngx_http_upstream_keepalive_module. Was wondering
why nginx uses a kind of two linkedlist based stack implementation to
implement keepalive connection pool. Why not use  typical linkedlist based
queue implementation.
Kindly refer to ngx_http_upstream_keepalive_module.c
:ngx_http_upstream_get_keepalive_peer
ngx_http_upstream_keepalive_module.c:ngx_http_upstream_free_keepalive_peer

I used exactly like this without wondering why, now I kind of want to know
the reason.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,251033,251033#msg-251033