Sujet : Re: Futexes ain't fast
De : chris.m.thomasson.1 (at) *nospam* gmail.com (Chris M. Thomasson)
Groupes : comp.lang.c++Date : 29. Aug 2024, 06:18:45
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <vaosr5$3ra5a$3@dont-email.me>
References : 1 2 3 4
User-Agent : Mozilla Thunderbird
On 8/28/2024 9:17 PM, Chris M. Thomasson wrote:
On 8/28/2024 8:51 PM, Bonita Montero wrote:
Am 28.08.2024 um 20:52 schrieb Chris M. Thomasson:
On 8/28/2024 5:09 AM, Bonita Montero wrote:
I tested the operating-system specific mutex (CRITICAL_SECTION Or
pthread_mutext_t) against a futex and a std::mutex. I guessed std::mutex
uses th operating system specific mutex internally, but the times varied
so much across Windows and Linux that I gues that std::mutex used at
least a differently parametrized operating system mutex or maybe even
completely own code.
This are the times and each line has a further contender:
[...]
while( futex.exchange( true, memory_order_acquire ) )
futex.wait( true, memory_order_relaxed );
futex.exchange( false, memory_order_release );
futex.notify_one();
} );
[...]
>
A wait bit would help out here... ;^) Afaict, this is a rather "naive" use of futexes. In you use case here, the exchange to unlock can be a simple atomic store with release semantics. Also, try to think about calling notify_* only when you absolutely need to... :^)
>
Show me your code ...
>
I did a while back for a futex mutex, win32 impl iirc... Do I have to find the older code?
Lets see... It's a bit hard to find for some reason:
https://groups.google.com/g/comp.lang.c++/c/1MZvhswJ6DQ/m/qyaYH-i0CgAJ