std::stop_token::stop_possible
Checks if the stop_token object has associated stop-state, and that state either has already had a stop requested or it has associated std::stop_source object(s).
A default constructed stop_token has no associated stop-state, and thus cannot be stopped; the associated stop-state for which no std::stop_source object(s) exist can also not be stopped if such a request has not already been made.
Contents
[edit] Parameters
(none)
[edit] Return value
false if the stop_token object has no associated stop-state, or it did not yet receive a stop request and there are no associated std::stop_source object(s); true otherwise.
[edit] Notes
If the stop_token object has associated stop-state and a stop request has already been made, this function still returns true.
If the stop_token object has associated stop-state from a std::jthread —for example, the stop_token was retrieved by invoking get_stop_token() on a std::jthread object—then this function always returns true. A std::jthread always has an internal std::stop_source object, even if the thread's invoking function does not check it.
[edit] Example
#include <chrono> #include <condition_variable> #include <format> #include <iostream> #include <mutex> #include <string_view> #include <thread> using namespace std::chrono_literals; int main() { std::cout << std::boolalpha ; auto print = [](std::string_view name, const std::stop_token & token) { std::cout << std::format ("{}: stop_possible = {:s}, stop_requested = {:s}\n", name, token.stop_possible(), token.stop_requested() ); }; // A worker thread that will listen to stop requests auto stop_worker = std::jthread ([](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 worker thread that will only stop when completed auto inf_worker = std::jthread ([]() { for (int i = 5; i; --i) { std::this_thread::sleep_for (300ms); std::cout << " Run as long as we want\n"; } }); std::stop_token def_token; std::stop_token stop_token = stop_worker.get_stop_token(); std::stop_token inf_token = inf_worker.get_stop_token(); print("def_token ", def_token); print("stop_token", stop_token); print("inf_token ", inf_token); std::cout << "\nRequest and join stop_worker:\n"; stop_worker.request_stop(); stop_worker.join(); std::cout << "\nRequest and join inf_worker:\n"; inf_worker.request_stop(); inf_worker.join(); std::cout << '\n'; print("def_token ", def_token); print("stop_token", stop_token); print("inf_token ", inf_token); }
Possible output:
def_token : stop_possible = false, stop_requested = false stop_token: stop_possible = true, stop_requested = false inf_token : stop_possible = true, stop_requested = false Request and join stop_worker: Run as long as we want Sleepy worker is requested to stop Request and join inf_worker: Run as long as we want Run as long as we want Run as long as we want Run as long as we want def_token : stop_possible = false, stop_requested = false stop_token: stop_possible = true, stop_requested = true inf_token : stop_possible = true, stop_requested = true