Http Keepalive implementation

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

Hello!

On Thu, Jun 19, 2014 at 01:24:53AM -0400, prkumar wrote:

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

The upstream keepalive module uses the “cache” queue as an LRU
queue, to be able to drop unused connections if there isn’t enough
room. Hence it basically uses it as a stack while storing /
retrieving connections.

The “free” queue is used to avoid runtime allocations.


Maxim D.
http://nginx.org/

Hello,

It seems ZMQ and Nginx keep coming up in conversations lately. There
seems
to be differing opinions on it’s performance/feasibility in production.
Do
you plan to open source your code? I’d be curious to look at it.

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