std::jthread::request_stop(3)

NAME
std::jthread::request_stop - std::jthread::request_stop

Synopsis
   bool request_stop() noexcept; (since C++20)
   Issues a stop request to the internal stop-state, if it has not yet already had stop
   requested.
   The determination is made atomically, and if stop was requested, the stop-state is
   atomically updated to avoid race conditions, such that:
     * stop_requested() and stop_possible() can be concurrently invoked on other
       std::stop_tokens and std::stop_sources of the same shared stop-state
     * request_stop() can be concurrently invoked from multiple threads on the same
       jthread object or on other std::stop_source objects associated with the same
       stop-state, and only one will actually perform the stop request
   However, see the Notes section.

Parameters
   (none)

Return value
   true if this invocation made a stop request, otherwise false

Postconditions
   For a std::stop_token retrieved by get_stop_token() or a std::stop_source retrieved
   by get_stop_source(), stop_requested() is true.

Notes
   If the request_stop() does issue a stop request (i.e., returns true), then any
   std::stop_callbacks registered for the same associated stop-state will be invoked
   synchronously, on the same thread request_stop() is issued on. If an invocation of a
   callback exits via an exception, std::terminate is called.
   If a stop request has already been made, this function returns false. However there
   is no guarantee that another thread or std::stop_source object which has just
   (successfully) requested stop for the same stop-state is not still in the middle of
   invoking a std::stop_callback function.
   If the request_stop() does issue a stop request (i.e., returns true), then all
   condition variables of base type std::condition_variable_any registered with an
   interruptible wait for std::stop_tokens associated with the jthread's internal
   stop-state will be awoken.

Example
// Run this code
 #include <iostream>
 #include <thread>
 #include <chrono>
 #include <mutex>
 #include <condition_variable>
 using namespace std::chrono_literals;
 int main()
 {
     // A sleepy worker thread
     std::jthread sleepy_worker([](std::stop_token stoken) {
         for (int i = 10; i; --i) {
             std::this_thread::sleep_for(300ms);
             if (stoken.stop_requested()) {
                 std::cout << "Sleepy worker is requested to stop\n";
                 return;
             }
             std::cout << "Sleepy worker goes back to sleep\n";
         }
     });
     // A waiting worker thread
     // The condition variable will be awoken by the stop request.
     std::jthread waiting_worker([](std::stop_token stoken) {
         std::mutex mutex;
         std::unique_lock lock(mutex);
         std::condition_variable_any().wait(lock, stoken,
             [&stoken] { return false; });
         if (stoken.stop_requested()) {
             std::cout << "Waiting worker is requested to stop\n";
             return;
         }
     });
     // std::jthread::request_stop() can be called explicitly:
     std::cout << "Requesting stop of sleepy worker\n";
     sleepy_worker.request_stop();
     sleepy_worker.join();
     std::cout << "Sleepy worker joined\n";
     // Or automatically using RAII:
     // waiting_worker's destructor will call request_stop()
     // and join the thread automatically.
 }

Possible output:
 Requesting stop of sleepy worker
 Sleepy worker is requested to stop
 Sleepy worker joined
 Waiting worker is requested to stop