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(....)
}

> Where `container_lock` is some kind of type that is able to lock the
> mutex *and* communicate to the container that it has locked the mutex,
> so the container shouldn't lock it. But that flag is conceptually
> thread-local; it *must only* be checked by calls into the container
> from the thread that did a `container_lock`. All other threads must
> lock the mutex.
>
> So basically instead of a flag, it needs to be a thread ID. And I'm
> not even sure this doesn't constitute a race condition of some sort.

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