Re: Futexes ain't fast

On 8/29/2024 12:20 PM, Chris M. Thomasson wrote:

On 8/29/2024 7:30 AM, Bonita Montero wrote:

This is by far the fastest code:
>
#if defined(_WIN32)
     HANDLE hSem = CreateSemaphoreA( nullptr, 0, 0x7FFFFFFF, nullptr );
     auto acquire = [&] { WaitForSingleObject( hSem, INFINITE ); };
     auto release = [&] { ReleaseSemaphore( hSem, 1, nullptr ); };

^^^^^^^^^^^^^^^^^^^^^^
 Actually, release can be SetEvent because the mutex logic only needs a binary semaphore, or an event on windows. However, I cannot remember if an event is "faster" than a semaphore on windows or not. Still do not know how windows handles it's futexes wrt internal impl. WaitOnAddress and such.

[...]
Not sure if you are familiar with them, but I do remember a special type of event on Windows in the kernel. Iirc, they were called keyed events. Still not sure how Windows implements WaitOnAddress.