[x265] [PATCH 1 of 2] Add support for customizing logging

[Ashok Kumar Mishra]

On Mon, Mar 19, 2018 at 3:59 AM, Andrey Semashev <andrey.semashev at gmail.com>
wrote:

> On 03/18/18 20:04, Derek Buitenhuis wrote:
>
>> On 3/16/2018 3:28 PM, Andrey Semashev wrote:
>>
>>> +/* x265_set_log:
>>> + *       Sets a custom logger function */
>>> +void x265_set_log(x265_log_t log);
>>>
>>
>> I would like to voice my distaste for this implementation.
>>
>> This is a global callback, and will introduce problems with e.g. multiple
>> libraries or dependencies in a program have libx265 as a dependency, or
>> even
>> with multiple encoders in the same program are used.
>>
>> Consider program A that has B as a dependency, both of which use libx265:
>>
>> A - libx265
>>    - B
>>        - libx265
>>
>> Either A or B could set the log callback for x265, and it would take
>> over for both. This is not ideal, and it is the same design mistake
>> we at FFmpeg made a long time ago, which has been haunting us for years.
>>
>
> Normally, there is only one _application_. There may be multiple
> _libraries_ using libx265 but none of them should be configuring its
> logging, unless it is supposed to be the only one using libx265 in the
> application (and generic libraries cannot make that assumption). It is the
> application that should configure logging in every component it uses.
>
> That said, I myself would prefer to configure logging on per-encoder
> basis, although for different reasons. But the way x265 is currently
> written does not allow this because in many places logging is done without
> any encoder context. I'm not willing to rewrite x265 to support this as
> global logging customization is "good enough" for me. It certainly is much
> better than unconditionally logging to stdout.
>
> Further, defining user types ending in _t is not allowed in C (which this
>> header is, and is used from), and x265 does not do this.
>>
>
> I'm not aware of this limitation. In particular, C11 section 7.1.3
> contains no such restriction. Can you provide a reference to the part of
> the C standard that says this?
>
> Note also that the name starts with x265, so it clearly belongs to the
> x265 namespace and is unlikely to clash with anything.
>
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>


I completely agree with Derek. First of all global logging is not a good
idea and second,
it will create problem for other applications using multiple instances of
x265.
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