[FFmpeg-devel] [PATCH] avutil/executor: Fix missing check before using mutex

[Zhao Zhili]

> On Jul 1, 2024, at 21:14, Nuo Mi <nuomi2021 at gmail.com> wrote:
> 
> On Sun, Jun 30, 2024 at 6:45 PM Zhao Zhili <quinkblack at foxmail.com> wrote:
> 
>> From: Zhao Zhili <zhilizhao at tencent.com>
>> 
>> ---
>> The code can be simplified by always creating mutex/cond. I'm not sure
>> it worth the overhead. Please note !HAVE_THREADS don't have the same
>> problem since it has mock implementation of ff_mutex_lock/unlock.
>> 
> Hi Zhili,
> Thank you for the patch.
> Do we really need this? The lock/unlock/signal functions will return an
> error if the lock and condition variables are not initialized.

We have strict check in libavutil/thread.h, e.g.,

static inline int strict_pthread_mutex_lock(pthread_mutex_t *mutex)
{
    ASSERT_PTHREAD(pthread_mutex_lock, mutex);
}

The strict check is enabled when configure --assert-level=2.

> 
>> 
>> libavutil/executor.c | 9 ++++++---
>> 1 file changed, 6 insertions(+), 3 deletions(-)
>> 
>> diff --git a/libavutil/executor.c b/libavutil/executor.c
>> index fb20104b58..89058fab2f 100644
>> --- a/libavutil/executor.c
>> +++ b/libavutil/executor.c
>> @@ -194,14 +194,17 @@ void av_executor_execute(AVExecutor *e, AVTask *t)
>>     AVTaskCallbacks *cb = &e->cb;
>>     AVTask **prev;
>> 
>> -    ff_mutex_lock(&e->lock);
>> +    if (e->thread_count)
>> +        ff_mutex_lock(&e->lock);
>>     if (t) {
>>         for (prev = &e->tasks; *prev && cb->priority_higher(*prev, t);
>> prev = &(*prev)->next)
>>             /* nothing */;
>>         add_task(prev, t);
>>     }
>> -    ff_cond_signal(&e->cond);
>> -    ff_mutex_unlock(&e->lock);
>> +    if (e->thread_count) {
>> +        ff_cond_signal(&e->cond);
>> +        ff_mutex_unlock(&e->lock);
>> +    }
>> 
>>     if (!e->thread_count || !HAVE_THREADS) {
>>         // We are running in a single-threaded environment, so we must
>> handle all tasks ourselves
>> --
>> 2.42.0
>> 
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