std::stop_callback
<stop_token>
class stop_callback;
The stop_callback class template provides an RAII object type that registers a callback function for an associated std::stop_token object, such that the callback function will be invoked when the std::stop_token's associated std::stop_source is requested to stop.
Callback functions registered via stop_callback's constructor are invoked either in the same thread that successfully invokes request_stop() for a std::stop_source of the stop_callback's associated std::stop_token; or if stop has already been requested prior to the constructor's registration, then the callback is invoked in the thread constructing the stop_callback.
More than one stop_callback can be created for the same std::stop_token, from the same or different threads concurrently. No guarantee is provided for the order in which they will be executed, but they will be invoked synchronously; except for stop_callback(s) constructed after stop has already been requested for the std::stop_token, as described previously.
If an invocation of a callback exits via an exception then std::terminate is called.
std::stop_callback is not CopyConstructible, CopyAssignable, MoveConstructible, nor MoveAssignable.
The template param Callback type must be both invocable and destructible. Any return value is ignored.
[edit] Member types
callback_type
Callback
[edit] Member functions
[edit] Deduction guides
[edit] Example
#include <chrono> #include <condition_variable> #include <iostream> #include <mutex> #include <sstream> #include <thread> using namespace std::chrono_literals; // Use a helper class for atomic std::cout streaming. class Writer { std::ostringstream buffer; public: ~Writer() { std::cout << buffer.str(); } Writer& operator<<(auto input) { buffer << input; return *this; } }; int main() { // A worker thread. // It will wait until it is requested to stop. std::jthread worker([] (std::stop_token stoken) { Writer() << "Worker thread's id: " << std::this_thread::get_id () << '\n'; std::mutex mutex; std::unique_lock lock(mutex); std::condition_variable_any ().wait(lock, stoken, [&stoken] { return stoken.stop_requested(); }); }); // Register a stop callback on the worker thread. std::stop_callback callback(worker.get_stop_token(), [] { Writer() << "Stop callback executed by thread: " << std::this_thread::get_id () << '\n'; }); // Stop_callback objects can be destroyed prematurely to prevent execution. { std::stop_callback scoped_callback(worker.get_stop_token(), [] { // This will not be executed. Writer() << "Scoped stop callback executed by thread: " << std::this_thread::get_id () << '\n'; }); } // Demonstrate which thread executes the stop_callback and when. // Define a stopper function. auto stopper_func = [&worker] { if (worker.request_stop()) Writer() << "Stop request executed by thread: " << std::this_thread::get_id () << '\n'; else Writer() << "Stop request not executed by thread: " << std::this_thread::get_id () << '\n'; }; // Let multiple threads compete for stopping the worker thread. std::jthread stopper1(stopper_func); std::jthread stopper2(stopper_func); stopper1.join(); stopper2.join(); // After a stop has already been requested, // a new stop_callback executes immediately. Writer() << "Main thread: " << std::this_thread::get_id () << '\n'; std::stop_callback callback_after_stop(worker.get_stop_token(), [] { Writer() << "Stop callback executed by thread: " << std::this_thread::get_id () << '\n'; }); }
Possible output:
Worker thread's id: 140460265039616 Stop callback executed by thread: 140460256646912 Stop request executed by thread: 140460256646912 Stop request not executed by thread: 140460248254208 Main thread: 140460265043776 Stop callback executed by thread: 140460265043776