[FFmpeg-devel] [PATCH] pthread: Allow thread_count==0

[Jason Garrett-Glaser]

2011/2/20 M?ns Rullg?rd <mans at mansr.com>:
> Alexander Strange <astrange at ithinksw.com> writes:
>
>> 2011/2/19 M?ns Rullg?rd <mans at mansr.com>:
>>> Takashi Mochizuki <mochi at da2.so-net.ne.jp> writes:
>>>
>>>> Some codec like libx264 uses thread_count==0 as Automatic mode.
>>>>
>>>> But, "Frame-based multithreading framework using pthreads"
>>>> ?(commit: 37b00b47cbeecd66bb34c5c7c534d016d6e8da24)
>>>> does not allow thread_count==0.
>>>>
>>>> Here is a tiny patch.
>>>>
>>>> Takashi Mochizuki
>>>>
>>>> //
>>>>
>>>> ---
>>>> ?libavcodec/pthread.c | ? ?2 +-
>>>> ?1 files changed, 1 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/libavcodec/pthread.c b/libavcodec/pthread.c
>>>> index 0e033d3..6b989ac 100644
>>>> --- a/libavcodec/pthread.c
>>>> +++ b/libavcodec/pthread.c
>>>> @@ -877,7 +877,7 @@ int ff_thread_init(AVCodecContext *avctx, int thread_count)
>>>> ? ? ? ? ?return -1;
>>>> ? ? ?}
>>>>
>>>> - ? ?avctx->thread_count = FFMAX(1, thread_count);
>>>> + ? ?avctx->thread_count = FFMAX(0, thread_count);
>>>
>>> I'm pretty sure this has come up before, and that there was some reason
>>> for things being as they are. ?I don't remember the details without
>>> digging in the archives.
>>
>> The issue only just appeared.
>> https://roundup.ffmpeg.org/issue2609
>
> I was thinking of the old threading model. ?Sorry for the confusion.
>
>> This patch actually does work ATM (didn't test it, just thought a
>> little), but I think I have other pending code that expects
>> thread_count >= 1, because it allocates things with sizeof(obj) *
>> thread_count.
>>
>> The best approach would be a CODEC_CAP_AUTO_THREADS defined for
>> external libraries that can decide on # threads themselves; it could
>> pass through 0 as a value to them, but otherwise cap it to 1. I would
>> apply this first to fix x264 and then come back to it.
>
> Sounds reasonable.

If nobody fixes this, I'm ripping threads support out of libx264.c by
Friday, i.e. forcing auto threads.  This is an ultimatum.

Also, a user is reporting that on his system, -threads 32 uses 6
threads in x264.

Jason