std::stop_callback
Defined in header <stop_token> | ||
template<class Callback > class stop_callback; | (since C++20) | |
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.
Contents |
[edit]Member types
| Type | Definition |
callback_type | Callback |
[edit]Member functions
constructs new stop_callback object (public member function) | |
destructs the stop_callback object (public member function) | |
operator= [deleted] | stop_callback is not assignable (public member function) |
[edit]Deduction guides
[edit]Example
#include <chrono>#include <condition_variable>#include <iostream>#include <mutex>#include <sstream>#include <thread> usingnamespace 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
