Re: signalling a condvar from inside vs. signalling a condvar von outside

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; } );

                     --signalled;