Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: signalling a condvar from inside vs. signalling a condvar von
 outside
Date: Thu, 24 Apr 2025 13:15:57 -0700
Organization: A noiseless patient Spider
Lines: 42
Message-ID: <vue65u$2aggi$2@dont-email.me>
References: <vte0g6$pmgv$1@raubtier-asyl.eternal-september.org>
 <vtpcnt$384n4$1@dont-email.me>
 <vtpu86$3qnsh$1@raubtier-asyl.eternal-september.org>
 <vtq3dt$3vg77$1@dont-email.me>
 <vtqo57$hi7r$1@raubtier-asyl.eternal-september.org>
 <vtrf3u$15mgp$1@dont-email.me>
 <vtsph1$2d55o$1@raubtier-asyl.eternal-september.org>
 <vtu9un$3mhje$1@dont-email.me>
 <vtub8i$3o27s$1@raubtier-asyl.eternal-september.org>
 <nPOMP.335105$j2D.258162@fx09.iad>
 <vu0f8m$1nm7v$2@raubtier-asyl.eternal-september.org>
 <eVVMP.1467426$BrX.929148@fx12.iad> <vu3obr$kp0a$2@dont-email.me>
 <vu4j24$1fq9b$1@raubtier-asyl.eternal-september.org>
 <vu6nrs$3b29s$1@dont-email.me>
 <vu78mg$3t3v4$1@raubtier-asyl.eternal-september.org>
 <vu925c$1esv8$1@dont-email.me>
 <vu9uqk$2bldm$1@raubtier-asyl.eternal-september.org>
 <vue5hl$2aggi$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Date: Thu, 24 Apr 2025 22:15:59 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="9ab23ff6e21fe9bbc243a2a98cfc6588";
	logging-data="2441746"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/3eJnaVBKaE92+WcEMYgc/J7p9ELixemE="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:RgRFXNBrgATy+Al8+FDWZB5eQ1E=
In-Reply-To: <vue5hl$2aggi$1@dont-email.me>
Content-Language: en-US
Bytes: 3251

On 4/24/2025 1:05 PM, Chris M. Thomasson wrote:
> On 4/22/2025 10:46 PM, Bonita Montero wrote:
>> Now I wrote a little program to test if there's thundering herd problem
>> with glibc's mutex / condvar. This it is:
>>
>> #include <iostream>
>> #include <thread>
>> #include <mutex>
>> #include <condition_variable>
>> #include <atomic>
>> #include <semaphore>
>> #include <vector>
>> #include <sys/resource.h>
>>
>> using namespace std;
>>
>> int main()
>> {
>>      constexpr size_t N = 10'000;
>>      int nClients = thread::hardware_concurrency() - 1;
>>      mutex mtx;
>>      int signalled = 0;
>>      condition_variable cv;
>>      atomic_int ai( 0 );
>>      binary_semaphore bs( false );
>>      vector<jthread> clients;
>>      atomic_int64_t nVoluntary( 0 );
>>      for( int c = nClients; c; --c )
>>          clients.emplace_back( [&]
>>              {
>>                  for( size_t r = N; r; --r )
>>                  {
>>                      unique_lock lock( mtx );
>>                      cv.wait( lock, [&] { return (bool)signalled; } );

I must be missing something here.  Where is your predicate for your 
cv.wait?

>>                      --signalled;

[...]