Re: [boost] Fwd: Futex using boost, threads never wakeup

On 2/23/23 19:14, oliver.kowalke--- via Boost wrote:

Code from namespace detail is not part of the public API. Do  not use this code (boost::fiber::detail::futex).

Also, if you can't use waiting/notifying operations in std::atomic, I suggest using Boost.Atomic instead.

23.02.2023 14:51:39 tsoumplekas_giorgos via Boost :

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Subject: Futex using boost, threads never wakeup Hello all I posted the following question in stackoverflow https://stackoverflow.com/questions/75538799/futex-using-boost-threads-never... 0 https://stackoverflow.com/posts/75538799/timeline

I am studying about futex synchronisation Following up the manual https://man7.org/linux/man-pages/man2/futex.2.html , I tried to syncroniaze threads using boost futex However the threads never wake up

#include <iostream>#include <atomic>#include #include <thread>#include <vector>#include <chrono>void wait(std::atomic<int>  & futexp){     int one = 1;     while(std::atomic_compare_exchange_strong(&futexp, &one, 0))     {}     std::cout << std::this_thread::get_id() << "," << futexp.load() << std::endl;     boost::fibers::detail::futex_wait(&futexp,0);    // std::this_thread::sleep_for(std::chrono::milliseconds(5000));

}void fpost(std::atomic<int>  & futexp){     int zero = 0;     if (std::atomic_compare_exchange_strong(&futexp, &zero, 1)) {      boost::fibers::detail::futex_wake(&futexp);     } }

std::atomic<int>  futexp{1};int main() {     std::vectorstd::thread  vec;     for(int i =0 ; i< 5;++i)     {         vec.emplace_back([]()         {             wait(futexp);             fpost(futexp);         });     }

Code demo https://godbolt.org/z/94hMsrW4a

I am using boost 1.66 and gcc 9.1 What goes wrong with this piece of code ?

Who is going to wake the first thread? Also, your code is not protected against spurious wakeups.