c++ - How to stop a async evaluating function on timeout? -

say have simple async call want kill/terminate/eliminate on timeout

// future::wait_for #include <iostream>       // std::cout #include <future>         // std::async, std::future #include <chrono>         // std::chrono::milliseconds  // non-optimized way of checking prime numbers: bool is_prime (int x) {   (int i=2; i<x; ++i) if (x%i==0) return false;   return true; }  int main () {   // call function asynchronously:   std::future<bool> fut = std::async (is_prime,700020007);     // while waiting function set future:   std::cout << "checking, please wait";   std::chrono::milliseconds span (100);   while (fut.wait_for(span)==std::future_status::timeout)     std::cout << '.';    bool x = fut.get();    std::cout << "\n700020007 " << (x?"is":"is not") << " prime.\n";    return 0; } 

we want kill first timeout happens. cant find method in future.

the closest find stop running task std::packaged_task reset method yet not if can interrupt running task. how 1 kills task running asyncrinusly not using boost thread or other non stl libraries?

it's not possible stop std::async out of box... however, can this, pass bool terminate is_prime method , throw exception if there timeout:

// future::wait_for #include <iostream>       // std::cout #include <future>         // std::async, std::future #include <chrono>         // std::chrono::milliseconds    // non-optimized way of checking prime numbers: bool is_prime(int x, std::atomic_bool & run) {     (int = 2; < x && run; ++i)     {         if (x%i == 0) return false;     }      if (!run)     {         throw std::runtime_error("timeout");     }      return true; }  int main() {     // call function asynchronously:     std::atomic_bool run;     run = true;     std::future<bool> fut = std::async(is_prime, 700020007, std::ref(run));      // while waiting function set future:     std::cout << "checking, please wait";     std::chrono::milliseconds span(100);     while (fut.wait_for(span) == std::future_status::timeout)     {         std::cout << '.';         run = false;     }      try     {         bool x = fut.get();         std::cout << "\n700020007 " << (x ? "is" : "is not") << " prime.\n";     }     catch (const std::runtime_error & ex)     {         // handle timeout here     }      return 0; } 

why begin able stop thread bad.

stopping threads @ arbitrary point dangerous , lead resource leaks, resources being pointers, handles files , folders, , other things program should do.

when killing thread, thread may or may not doing work. whatever doing, won’t complete , variables created not destructors called because there no thread run them on.

i have outlined of issues here.