The very idea of a mutex is that it is synchronous. You wait until you can acquire the mutex.

If it's asynchronous, it's not a mutex anymore, or it's just used to synchronously setup some other asynchronous mechanism.

▲ gpderetta 10 hours ago | parent [-]

A mutex is a way to guarantee mutual exclusion nothing more nothing less; You can recover synchronous behaviour if you really want:

    synchronized<Something> something;
    ...
    co_await something.async_visit([&](Something& x) {
        /* critical section here */ 
    });

▲ mgaunard 10 hours ago | parent [-]

that isn't a mutex, that's delegating work asynchronously and delegating something else to run when it is complete (the implicitly defined continuation through coroutines).

In systems programming parlance, a mutex is a resource which can be acquired and released, acquired exactly once, and blocks on acquire if already acquired.

▲ gpderetta 10 hours ago | parent [-]

Do a CPS transform of your typical std::mutex critical section and you'll find they are exactly the same.

▲ mgaunard 9 hours ago | parent [-]

They're not, the interactions with the memory model are different, as are the guarantees.

CPS shouldn't be able to deadlock for example?

	▲	gpderetta 9 hours ago \| parent [-]
		CPS can trivially deadlock for all meaningful definitions of deadlock. Would you consider this a mutex? `async_mutex mux; co_await mux.lock(); /* critical section / co_await mux.unlock();` What about: my_mutex mux; `{ std::lock_guard _{mux}; / critical section */ }` where the code runs in a user space fiber. Would you consider boost synchronized a mutex? Don't confuse the semantics with the implementation details (yes async/await leaks implementation details).