Re: Solving thundering Herd with glibc...

On 4/26/2025 12:25 AM, Bonita Montero wrote:

Am 26.04.2025 um 08:26 schrieb Bonita Montero:

Am 25.04.2025 um 22:01 schrieb Chris M. Thomasson:
>
 > If you say so... Too busy right now. Perhaps sometime later on tonight.
>
>
If there would be a thundering herd problem with glibc's condvar it
would happen very often with my code since I awake 31 threads at once
with my machine.

 I just tried to awaken all 31 threads from outside holding the mutex,
but not from inside:
      for( size_t r = N; r; --r )
     {
         unique_lock lock( mtx );
         signalled = nClients;
         ai.store( nClients, memory_order_relaxed );
         lock.unlock();
         if( argc < 2 )
             cv.notify_all();
         else
             for( int c = nClients; c; cv.notify_one(), --c );
         bs.acquire();
     }
 The result: 7.500 context switches per thread, not 3.000.
      10000 rounds,
     7498.06 context switches pe thread
 So never signal a condvar to multiple threads from outside !

So, do that. It's your software. Do what you like. This is a very old debate. Take your contrived test and just, roll with it. Whatever.