ngx_http_cleanup_add

[Dk Jack]

Thanks Maxim,
Thanks for the suggestion about using ngx_pool_cleanup_add. Since this is
external library memory I couldn't use ngx_pcalloc. Thanks again.

On Wed, Nov 10, 2021 at 7:47 PM Maxim Dounin <mdounin at mdounin.ru> wrote:

> Hello!
>
> On Wed, Nov 10, 2021 at 07:22:50PM -0800, Dk Jack wrote:
>
> > Hi,
> > In my module, I am allocating some memory for each request and saving the
> > ptr in my module context. I am registering a callback using
> > ngx_http_cleanup_add to perform cleanup for each request. I am releasing
> > the memory for the allocation in the cleanup callback. In the log phase,
> I
> > want to make available the contents of the memory I allocated as an nginx
> > variable.
> >
> > However, when I try to print this variable in the log, the memory has
> > already been de-allocated. It looks like the clean-up handlers are called
> > before the log phase. Since I have released the memory in the cleanup
> > handler, I have nothing to log in the log phase. Is there a way to defer
> > the calling of the clean-up handler until after the log phase?
>
> Request cleanup handlers as allocated by ngx_http_cleanup_add()
> are expected to be called before logging: these are used to stop
> various activities which might still be going on when nginx
> decides to terminate the request.  Notably, it used by the
> upstream module to close upstream connections.
>
> If you want to free the memory, a better idea would be to use pool
> cleanup handlers instead, which are registered by the
> ngx_pool_cleanup_add() function.  These are called while actually
> freeing request memory, after all request processing is completely
> finished, including logging.  See here for details:
>
> http://nginx.org/en/docs/dev/development_guide.html#memory_management
>
> Note well that for per-request allocations it is usually better to
> simply allocate memory from the request pool via ngx_palloc(), so
> it is freed automatically when the request pool is destroyed.
> Pool cleanup handlers are mostly needed to free various external
> resources, such as file descriptors or memory from external
> libraries.
>
> --
> Maxim Dounin
> http://mdounin.ru/
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> nginx-devel mailing list
> nginx-devel at nginx.org
> http://mailman.nginx.org/mailman/listinfo/nginx-devel
>
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