On 5/28/23 11:23, Jason McKesson via Std-Proposals wrote:
> On Sun, May 28, 2023 at 11:18 AM Phil Bouchard <boost_at_[hidden]> wrote:
>>
>>
>>
>> On 5/28/23 11:13, Jason McKesson via Std-Proposals wrote:
>>> On Sun, May 28, 2023 at 11:04 AM Federico Kircheis via Std-Proposals
>>> <std-proposals_at_[hidden]> wrote:
>>>>
>>>> On 28/05/2023 16.55, Phil Bouchard via Std-Proposals wrote:
>>>>> This is pretty much what I had in mind:
>>>>> https://github.com/philippeb8/std__ts/blob/master/ts.h
>>>>>
>>>>> Very cost / beneficial.
>>>>>
>>>>
>>>>
>>>> One of the issues I have with such classes is that they make other tools
>>>> for finding bugs, like sanitizers and valgrind, useless.
>>>>
>>>> This code is racy, even with the internal mutex:
>>>>
>>>> if(container.empty()){
>>>> container.insert(....)
>>>> }
>>>>
>>>>
>>>> but since the data is protected by mutexes and synchronized, not tools
>>>> will complain (AFAIK).
>>>>
>>>> Thus even if such class would be standardized, in most cases it is
>>>> useless/it is a not a good primitive for multi-threaded code.
>>>
>>> What's worse is that "fixing it" is really hard. You'd have to do
>>> something like this
>>>
>>> ```
>>> container_lock c(container);
>>> if(container.empty())
>>> {
>>> container.insert(....)
>>> }
>>> ```
>>
>> All you'd have to do is:
>>
>> std::lock_guard<std::mutex> lock(container.mutex());
>> if(container.empty())
>> {
>> container.insert(....)
>> }
>
> 1: Your example code has no such function.
>
> 2: All that would do is provoke UB. `empty` will attempt to lock the
> mutex. Locking a `std::mutex` that is already locked by your thread
> yields UB. You would need a `recursive_mutex`, which is basically the
> thing I described with thread IDs wrapped in its own object. In short:
> it adds overhead.

Yes I corrected myself in the other post.

But the overhead of mutices is not that bad also if it can save you from
these treacherous race-conditions.

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