missing module context

Anatoli Marinov toli at webforge.bg
Tue Jul 10 11:53:34 UTC 2012

I think I have only 1 request without any sub requests and also do not 
use internal redirects.

On 07/10/2012 01:24 PM, Valentin V. Bartenev wrote:
> On Tuesday 10 July 2012 14:17:11 Valentin V. Bartenev wrote:
>> 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.
> Btw, it also cleared by the internal redirect.
>   wbr, Valentin V. Bartenev
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