Hi
Ngx_list_t have create api but no free_list api
Why?
I wrote my own free_list, is anyone else face this issue?
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Hello!
On Tue, Apr 18, 2023 at 06:14:46AM +0000, Yuval Abadi via nginx wrote:
> Ngx_list_t have create api but no free_list api
>
> Why?
>
> I wrote my own free_list, is anyone else face this issue?
Much like many things in nginx, ngx_list_t structure is an
append-only structure, and it is expected to be used as a list of
items being added. Most notably, ngx_list_t is used for request
headers (these are added to the list when they are parsed), and
response headers (these are added when they are generated
internally).
If you have to remove an item for some reason (which shouldn't be
common case for legitimate usage, but might happen to be needed
occasionally), the common approach is to use a "skip" flag in the
structures being listed. For example, response headers are
cleared by setting the "hash" field to 0, so such headers are
ignored by the code iterating over the list.
If you need something more dynamic in your code, ngx_list_t might
not be the right structure to use. Something like ngx_queue_t or
ngx_rbtree_t might be a better choice.
--
Maxim Dounin
http://mdounin.ru/
Thanks
I just need list not queue,
And I want to free the whole list , not one node.
-----Original Message-----
From: nginx <nginx-bounces at nginx.org> On Behalf Of Maxim Dounin
Sent: Tuesday, 18 April 2023 15:36
To: Yuval Abadi via nginx <nginx at nginx.org>
Subject: Re: ngx_list_free
EXTERNAL MAIL: nginx-bounces at nginx.org
Hello!
On Tue, Apr 18, 2023 at 06:14:46AM +0000, Yuval Abadi via nginx wrote:
> Ngx_list_t have create api but no free_list api
>
> Why?
>
> I wrote my own free_list, is anyone else face this issue?
Much like many things in nginx, ngx_list_t structure is an append-only structure, and it is expected to be used as a list of items being added. Most notably, ngx_list_t is used for request headers (these are added to the list when they are parsed), and response headers (these are added when they are generated internally).
If you have to remove an item for some reason (which shouldn't be common case for legitimate usage, but might happen to be needed occasionally), the common approach is to use a "skip" flag in the structures being listed. For example, response headers are cleared by setting the "hash" field to 0, so such headers are ignored by the code iterating over the list.
If you need something more dynamic in your code, ngx_list_t might not be the right structure to use. Something like ngx_queue_t or ngx_rbtree_t might be a better choice.
--
Maxim Dounin
http://mdounin.ru/
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Hello!
On Tue, Apr 18, 2023 at 03:12:08PM +0000, Yuval Abadi via nginx wrote:
> Thanks
>
> I just need list not queue,
Queue is a double-linked list.
> And I want to free the whole list , not one node.
In nginx, memory allocations use pools, and in most cases you
cannot free individual allocations. The only options is to
destroy the whole pool.
For example, this naturally works with requests: all allocations
related to a request are done from the request pool, and are
automatically freed when the request is freed and its pool is
destroyed.
See here for more details about memory pools:
http://nginx.org/en/docs/dev/development_guide.html#pool
--
Maxim Dounin
http://mdounin.ru/