std::stop_token::stop_possible
bool stop_possible()constnoexcept; | (since C++20) | |
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>usingnamespace std::chrono_literals; int main(){std::cout<<std::boolalpha;auto print =[](std::string_view name, conststd::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 requestsauto 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 completedauto 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
