[FFmpeg-devel] [PATCH v1 1/4] avformat/dashenc: remove unused check of avformat_free_context

[Steven Liu]

> 在 2019年11月29日，13:57，Andreas Rheinhardt <andreas.rheinhardt at gmail.com> 写道：
> 
> Steven Liu:
>> 
>> 
>>> 在 2019年11月29日，13:40，Andreas Rheinhardt <andreas.rheinhardt at gmail.com> 写道：
>>> 
>>> Jeyapal, Karthick:
>>>> 
>>>> On 11/29/19 10:45 AM, Steven Liu wrote:
>>>>> Signed-off-by: Steven Liu <lq at chinaffmpeg.org>
>>>>> ---
>>>>> libavformat/dashenc.c | 3 +--
>>>>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>>>> 
>>>>> diff --git a/libavformat/dashenc.c b/libavformat/dashenc.c
>>>>> index a462876c13..8c28fb6b6e 100644
>>>>> --- a/libavformat/dashenc.c
>>>>> +++ b/libavformat/dashenc.c
>>>>> @@ -588,8 +588,7 @@ static void dash_free(AVFormatContext *s)
>>>>>                avio_close(os->ctx->pb);
>>>>>        }
>>>>>        ff_format_io_close(s, &os->out);
>>>>> -        if (os->ctx)
>>>>> -            avformat_free_context(os->ctx);
>>>>> +        avformat_free_context(os->ctx);
>>>> This 'if' condition is a safety net against double frees caused due to any corner case and/or wrong usage.
>>>> Unless this is absolutely required for some reason, this 'if' condition should not be removed.
>>> 
>>> This 'if' doesn't help against double-frees at all:
>>> avformat_free_context() itself checks against its argument being NULL
>>> and returns immediately if it is. (But double frees are still possible
>>> given that avformat_free_context can't reset the pointer to NULL due
>>> to its signature. Resetting is something the callers have to do for
>>> themselves.)
>> What about add reset pointer to NULL into the avformat_free_context?
> 
> This is pointless, because it will just reset the functions copy of
> the pointer to NULL, not the callers pointer to the AVFormatContext.
> In order to reset the latter, the parameter would have to be of type
> AVFormatContext ** (and the call here would be
> avformat_free_context(&os->ctx)).
AVFormatContext **? Isn’t that too complex for user of the API caller?
> 
> - Andreas
> 
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Thanks
Steven