Re: [FFmpeg-devel] [PATCH 2/2] avutil/executor: Fix stack overflow due to recursive call

[Nuo Mi <nuomi2021@gmail.com>]

On Tue, Jul 9, 2024 at 6:35 AM Timo Rothenpieler <timo@rothenpieler.org>
wrote:

> On 08.07.2024 17:32, Zhao Zhili wrote:
> >
> >
> >> On Jul 8, 2024, at 22:07, Timo Rothenpieler <timo@rothenpieler.org>
> wrote:
> >>
> >> On 08.07.2024 09:43, Zhao Zhili wrote:
> >>> From: Zhao Zhili <zhilizhao@tencent.com>
> >>> av_executor_execute run the task directly when thread is disabled.
> >>> The task can schedule a new task by call av_executor_execute. This
> >>> forms an implicit recursive call. This patch removed the recursive
> >>> call.
> >>> ---
> >>>   libavutil/executor.c | 5 +++++
> >>>   1 file changed, 5 insertions(+)
> >>> diff --git a/libavutil/executor.c b/libavutil/executor.c
> >>> index 89058fab2f..c145c51be9 100644
> >>> --- a/libavutil/executor.c
> >>> +++ b/libavutil/executor.c
> >>> @@ -58,6 +58,7 @@ struct AVExecutor {
> >>>       int die;
> >>>         AVTask *tasks;
> >>> +    int stack_depth;
> >>>   };
> >>>     static AVTask* remove_task(AVTask **prev, AVTask *t)
> >>> @@ -207,8 +208,12 @@ void av_executor_execute(AVExecutor *e, AVTask *t)
> >>>       }
> >>>         if (!e->thread_count || !HAVE_THREADS) {
> >>> +        if (e->stack_depth > 0)
> >>> +            return;
> >>> +        e->stack_depth++;
> >>>           // We are running in a single-threaded environment, so we
> must handle all tasks ourselves
> >>>           while (run_one_task(e, e->local_contexts))
> >>>               /* nothing */;
> >>> +        e->stack_depth--;
> >>
> >> Won't this put the above line into the "nothing" while-loop?
> >> Is that intended? If so, the indentation should be adjusted accordingly.
> >> If not, the while-loop should gain empty {}.
> >
> > The comment specify it’s a while loop with empty body. Maybe it’s not
> obvious
> > in the email client.
>
> Oh, there is a ; behind the comment.
> Completely missed that. Can't say I like it, but yeah, that works.
>
Google suggests using "while (cond) continue;":
https://google.github.io/styleguide/cppguide.html#Formatting_Looping_Branching
.
However, it's not better than using /* nothing */.

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