[[nodiscard]] bool stop_possible() const noexcept; | (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.
(none).
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.
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.
#include <chrono>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <string_view>
#include <thread>
#include <format>
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
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https://en.cppreference.com/w/cpp/thread/stop_token/stop_possible