On 2 January 2023 10:06:52 GMT, "Lénárd Szolnoki via Std-Proposals" <std-proposals_at_[hidden]> wrote:
>Hi,
>
>On 2 January 2023 03:22:31 GMT, Simon Scatton via Std-Proposals <std-proposals_at_[hidden]> wrote:
>>Hello everyone,
>>
>>I am currently implementing a generic logger that should be thread-safe.
>>To make sure I rewrite as little code as possible, I am templating a class as
>>follows:
>>
>>template <typename Mutex>
>>class Output
>>{
>>public:
>> void write();
>>protected:
>> Mutex mutex_;
>>};
>>
>>And I have a "null mutex" that is a struct like this:
>>struct NullMutex
>>{
>> void lock() {}
>> void unlock() noexcept {}
>> bool try_lock() { return true; }
>>};
>>
>>So that for instance if I want a thread safe Output, I use this:
>>Output<std::mutex> A;
>>And if I want a non-thread safe Output I use this:
>>Output<NullMutex> B;
>>
>>The core of the write() function being something like this:
>>
>>template <typename Mutex>
>>void Output<Mutex>::write()
>>{
>> const std::lock_guard<Mutex> lock(mutex_);
>> // ...
>>}
>>
>>I have not found any C++ official resources about this.
>>
>>Has this been already addressed in C++ standard discussion around
>>mutexes ? Do you think adding such a "null mutex" would be useful?
>>
>>I would love to hear what you think about this.
>>
>>Kind regards,
>>
>
>Yes, it definitely makes sense. I saw a similar type used in Boost.ASIO:
>
>https://github.com/boostorg/asio/blob/develop/include/boost/asio/detail/null_mutex.hpp#L29
>
>For example it is used for implementing basic_channel (null mutex) and basic_concurrent_channel (some regular mutex), employing the same pattern you described.
>
>I think it might be worth adding to the standard library.
>
>Cheers,
>Lénárd
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Apparently there is a public null_mutex class in Boost as well:

https://www.boost.org/doc/libs/1_81_0/boost/thread/null_mutex.hpp

It looks like a lot of boilerplate to satisfy the syntactic requirements of all the mutex concepts.

Cheers,
Lénárd