Re: [FFmpeg-devel] [PATCH 1/2] avutil/executor: Allowing thread_count be zero

From: Zhao Zhili <quinkblack@foxmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/2] avutil/executor: Allowing thread_count be zero
Date: Tue, 18 Jun 2024 22:23:57 +0800
Message-ID: <tencent_6D35BD805A34173E8F57819CCCE1585BBA09@qq.com> (raw)
In-Reply-To: <CAFXK13ez83GwuaO1VjRuziHVJ2+=XWE6Gg0BJa6Kke8bTOtpfw@mail.gmail.com>

> On Jun 18, 2024, at 19:50, Nuo Mi <nuomi2021@gmail.com> wrote:
> 
> On Mon, Jun 17, 2024 at 5:28 PM Zhao Zhili <quinkblack@foxmail.com> wrote:
> 
>> 
>> 
>>> On Jun 17, 2024, at 16:45, Hendrik Leppkes <h.leppkes@gmail.com> wrote:
>>> 
>>> On Mon, Jun 17, 2024 at 10:03 AM Zhao Zhili <quinkblack@foxmail.com>
>> wrote:
>>>> 
>>>> 
>>>> 
>>>>> On Jun 17, 2024, at 15:05, Anton Khirnov <anton@khirnov.net> wrote:
>>>>> 
>>>>> Quoting Zhao Zhili (2024-06-17 07:19:26)
>>>>>> From: Zhao Zhili <zhilizhao@tencent.com>
>>>>>> 
>>>>>> When thread_count be zero, it will be run on current thread like
>>>>>> !HAVE_THREADS.
>>>>> 
>>>>> Other APIs treat zero to mean "auto".
>>>> 
>>>> executor don’t detect cpu cores by itself. It’s more low level than
>> libavcodec.
>>>> 
>>>> Zero thread is zero thread, literally. If we use thread_count one to
>> mean
>>>> run on current thread, how to create a single thread then?
>>> 
>>> Whats the point of creating a single thread? Does the main thread ever
>>> do something else in the meantime, or does it just wait for the job
>>> anyway?
>> 
>> Executor as a basic infrastructure should support such usage. The caller
>> don’t need to wait for the job to finish.
>> 
> Hi Zhili,
> Thank you for the patch.
> Could you explain more about its usage?
> Why do we need to run everything in the main thread when we have pthread in
> the system?

In addition to match other decodes behavior, there are some usecases which
require the decoder to not create a thread at runtime. For example, when build
libavcodec with wasm and run in web browser, the runtime may or may not
support threads, threads number should be decided at runtime, and can be zero. 

> 
> Thank you.
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