is core Mutex lock "fast"?

[IGotD-]

On Tuesday, 26 January 2021 at 21:09:34 UTC, Steven Schveighoffer 
wrote:
>
> The only item that is read without being locked is owner. If 
> you change that to an atomic read and write, it should be fine 
> (and is likely fine on x86* without atomics anyway).
>
> All the other data is protected by the actual mutex, and so 
> should be synchronous.
>
> However, I think this is all moot, druntime is the same as 
> Tango.
>
> -Steve

Yes, I didn't see the lock would block subsequent threads.

Both pthread_mutex_lock and EnterCriticalSection do exactly the 
same as FastLock and the only difference is the the check is 
"closer" to the running code. Performance increase should be low.

As I was wrong about the thread safety, I will not write here any 
further.