The C Standard Library

C++ Library - <stop_token>

Quiz

The <stop_token> header in C++20, introduces a mechanism for cancellation of threads and asynchronous operations. It works in conjunction with the std::stop_source, which is responsible for generating stop requests.

These are used to implement a responsive systems that can halt operations without the need for forceful termination or complicated signaling mechanism.

Including <stop_token> Header

To include the <stop_token> header in your C++ program, you can use the following syntax.

#include <stop_token>

Functions of <stop_token> Header

Below is list of all functions from <stop_token> header.

Sr.No	Functions & Description
1	operator= It assigns the stop_token object.
2	swap It swaps two stop_token objects.
3	stop_requested It checks whether the associated stop-state has been requested to stop.
4	stop_possible It checks whether associated stop-state can be requested to stop.
5	get_token It returns a stop_token for the associated stop-state.

Using Multiple Threads with Stop Tokens

In the following example, we are going to use the std::stop_source to control the multiple threads.

#include <iostream>
#include <thread>
#include <stop_token>
#include <chrono>
void a(int id, std::stop_token b) {
   while (!b.stop_requested()) {
      std::cout << "A " << id << " Is Working.." << std::endl;
      std::this_thread::sleep_for(std::chrono::milliseconds(600));
   }
   std::cout << "A " << id << " Is Cancelled.." << std::endl;
}
int main() {
   std::stop_source x;
   std::thread x1(a, 1, x.get_token());
   std::thread x2(a, 2, x.get_token());
   std::this_thread::sleep_for(std::chrono::seconds(2));
   x.request_stop();
   x1.join();
   x2.join();
   return 0;
}

Output

Output of the above code is as follows −

A 2 Is Working..
A 1 Is Working..
A 2 Is Working..
A 1 Is Working..
A 2 Is Working..
A 1 Is Working..
A 2 Is Working..
A 1 Is Working..
A 2 Is Cancelled..
A 1 Is Cancelled..

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