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stop_token::stop_possible | ||||
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bool stop_possible()constnoexcept; | (since C++20) | |
Checks if thestop_token object has associated stop-state, and that state either has already had a stop requested or it has associatedstd::stop_source object(s).
A default constructedstop_token has no associated stop-state, and thus cannot be stopped; the associated stop-state for which nostd::stop_source object(s) exist can also not be stopped if such a request has not already been made.
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(none)
false if thestop_token object has no associated stop-state, or it did not yet receive a stop request and there are no associatedstd::stop_source object(s);true otherwise.
If thestop_token object has associated stop-state and a stop request has already been made, this function still returnstrue.
If thestop_token object has associated stop-state from astd::jthread—for example, thestop_token was retrieved by invokingget_stop_token() on astd::jthread object—then this function always returnstrue. Astd::jthread always has an internalstd::stop_source object, even if the thread's invoking function does not check it.
#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 = falsestop_token: stop_possible = true, stop_requested = falseinf_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 = falsestop_token: stop_possible = true, stop_requested = trueinf_token : stop_possible = true, stop_requested = true
