missing module context

[Valentin V. Bartenev]

On Tuesday 10 July 2012 12:31:45 Anatoli Marinov wrote:
> Hello Colleagues,
> I am working on a project, that uses nginx as http proxy and I have
> written many nginx modules. For several months till now I am looking for
> a bug in one of my modules but I cannot find it. It appears very rare
> but even so it should be fixed.
> 
> I added many log messages to debug the issue. I found that some time the
> module context is null even it has been set before.  I am using context
> functions as usual:
> 1. In rewrite phase :
> ctx = ngx_pcalloc(r->pool, sizeof(ngx_http_my_ctx_t));
> ngx_http_set_ctx(r, ctx, ngx_http_my_module);
> 
> 2. In log phase I am trying to get back my context :
> ctx = ngx_http_get_module_ctx(r, ngx_http_my_module);
> In this place ctx is NULL.
> 
> What is your opinion? Am am using this sequence on many places and it
> works as I expected but in this modules sometimes it fails.
> I think there could be a memory corruption issue. There could be a code
> that may write on request's context array and overwrite the context
> pointer. Is there a way to check this? Nginx uses its own memory pool
> system and tools like valgrind is not longer usable.
> 
> Please advise me how to find this issue...
> 
> All ideas are welcome!
> Best Regards
> 

The request context doesn't shared between subrequests. If you set ctx for 
subrequest and then trying to retrieve it for main request you will get NULL.

 wbr, Valentin V. Bartenev