Nginx event loop question

erik.l.nelson · 2015-06-01T22:51:24+00:00

Hello! On Mon, Jun 1, 2015 at 9:01 PM, erankor wrote: > I'm using nginx-headers-more to set a fixed last-modified header on the > responses of my serv...

Nginx event loop question

erik.l.nelson

In the Data Sharing section

http://wiki.nginx.org/HttpLuaModule#Data_Sharing_within_an_Nginx_Worker

there's a recommendation to share read-only data, and some caveats about sharing changeable data.

Just to make sure I understand correctly, as long as I'm in pure-lua code (no I/O), there won't be a race condition.

For example if I modified the dog's age in the example,

content_by_lua '
         local mydata = require "mydata"
         ngx.say(mydata.get_age("dog"))
         local newdog = mydata.data.dog .. tostring(mydata.data.dog):len()
         --will another copy ever run at this point?
         mydata.data.dog = newdog
       ';

Could I expect that mydata.data.dog would always be like

3123456789101214

and never become something like

311344456

I'm not sure if that's clear.

Thanks

Erik

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agentzh

Hello!

On Mon, Jun 1, 2015 at 10:51 PM, Nelson, Erik - 2 wrote:
> For example if I modified the dog's age in the example,
> content_by_lua '
>          local mydata = require "mydata"
>          ngx.say(mydata.get_age("dog"))
>          local newdog = mydata.data.dog .. tostring(mydata.data.dog):len()
>          --will another copy ever run at this point?
>          mydata.data.dog = newdog
>        ';
> Could I expect that mydata.data.dog would always be like
> 3123456789101214
> and never become something like
> 311344456

Correct. And even there's nonblocking I/O, the assignment itself is
always atomic. Thanks god that nginx workers are single-threaded
processes ;)

Regards,
-agentzh

erik.l.nelson

Yichun Zhang (agentzh) wrote on Saturday, June 13, 2015 7:06 AM
> Hello!
> 
> On Mon, Jun 1, 2015 at 10:51 PM, Nelson, Erik - 2 wrote:
> > For example if I modified the dog's age in the example,
> content_by_lua
> > '
> >          local mydata = require "mydata"
> >          ngx.say(mydata.get_age("dog"))
> >          local newdog = mydata.data.dog ..
> tostring(mydata.data.dog):len()
> >          --will another copy ever run at this point?
> >          mydata.data.dog = newdog
> >        ';
> > Could I expect that mydata.data.dog would always be like
> > 3123456789101214
> > and never become something like
> > 311344456
> 
> Correct. And even there's nonblocking I/O, the assignment itself is
> always atomic. Thanks god that nginx workers are single-threaded
> processes ;)
> 

Thanks again for a great project!

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