[vlc-devel] [PATCH] lib: assert instead of abort

[Steve Lhomme]

On 2019-09-27 17:33, Thomas Guillem wrote:
> 
> On Fri, Sep 27, 2019, at 17:28, Steve Lhomme wrote:
>> On 2019-09-27 16:41, Thomas Guillem wrote:
>>>
>>>
>>> On Fri, Sep 27, 2019, at 16:26, Rémi Denis-Courmont wrote:
>>>> Hi,
>>>>
>>>> I am on holidays without laptop, so I cannot check, but I believe the answer to your question is history. I mean, vlc_assert_unreachable() should be used there but it probably did not exist when the code was written.
>>>
>>> I don't like vlc_assert_unreachable(). I would prefer that this helper abort() instead or doing a __builtin_unreachable().
>>> Indeed,it is very hard to debug a code that reached this statement, everything is UB after that. I prefer to kill the process instead of making the app totally UB.
>>
>> When compiled in libvlc, vlc_assert_unreachable() asserts. So I think it
>> would work like an assert just fine.
>>
>> On the other hand, unreachable doesn't seem to signal the right issue in
>> code called by a libvlc user.
> 
> I mean vlc_assert_unreachable() if asserts are disabled (in release) is very painful to debug and cause a lot of UB. I prefer to abort() in that case.

In the rare case a libvlc app would have issues only in the release 
mode, then yes it's trickier to debug. One can always force asserts in a 
release build too.

>>
>>>>
>>>> Le 20 septembre 2019 15:49:50 GMT+03:00, Romain Vimont <rom1v at videolabs.io> a écrit :
>>>>> On Fri, Sep 20, 2019 at 03:13:08PM +0300, Rémi Denis-Courmont wrote:
>>>>>> I completely disagree. When event registration/deregistration fails, you're almost guaranteed a deadlock or some use after free. Much better to abort asap.
>>>>>
>>>>> If an assertion fails, then the program has (probably) undefined
>>>>> behavior.
>>>>>
>>>>> But why using assert() everywhere but abort() here? There are a lot of
>>>>> places where a failing assert() would almost guarantee a deadlock or
>>>>> some use after free.
>>>>>
>>>>>> Le 20 septembre 2019 12:21:37 GMT+03:00, Thomas Guillem <thomas at gllm.fr> a écrit :
>>>>>>> Because you should not abort in production. Developers will still be
>>>>>>> notified
>>>>>>> that they are miss-using the API with the assert.
>>>>>>>
>>>>>>> PS: this abort was happening on iOS via VLCKit, the API miss-use had
>>>>>>> been fixed
>>>>>>> here: https://code.videolan.org/videolan/VLCKit/merge_requests/19 lib/event.c | 2 +-
>>>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/lib/event.c b/lib/event.c
>>>>>>> index 28d3d0c232..4a57029b89 100644
>>>>>>> --- a/lib/event.c
>>>>>>> +++ b/lib/event.c
>>>>>>> @@ -179,5 +179,5 @@ void libvlc_event_detach(libvlc_event_manager_t
>>>>>>> *em, libvlc_event_type_t type,
>>>>>>>                 return;
>>>>>>>             }
>>>>>>>        }
>>>>>>> -    abort();
>>>>>>> +    assert(!"event not found or already detached");
>>>>>>>    }
>>>>>>> -- 
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>>>>>
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