Path: ...!news.nobody.at!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: Futexes ain't fast
Date: Wed, 28 Aug 2024 21:17:16 -0700
Organization: A noiseless patient Spider
Lines: 28
Message-ID: <vaosod$3ra5a$2@dont-email.me>
References: <van414$3fe9t$1@raubtier-asyl.eternal-september.org>
 <vanrkt$3j1oq$1@dont-email.me>
 <vaor7n$3r4u5$1@raubtier-asyl.eternal-september.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Date: Thu, 29 Aug 2024 06:17:17 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="98c6004928f46df0abe90729ccf8af51";
	logging-data="4040874"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX19oxCrbl9F3QslnIyxwOTxJMQ89MVsjG5g="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:77PMZHIQBOaOiRRmNnSXQm7zFvk=
Content-Language: en-US
In-Reply-To: <vaor7n$3r4u5$1@raubtier-asyl.eternal-september.org>
Bytes: 2507

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?