std::promise<R>::set_exception (3) - Linux Manuals

std::promise<R>::set_exception: std::promise<R>::set_exception

NAME

std::promise<R>::set_exception - std::promise<R>::set_exception

Synopsis

void set_exception( std::exception_ptr p ); (since C++11)

Atomically stores the exception pointer p into the shared state and makes the state ready.
The operation behaves as though set_value, set_exception, set_value_at_thread_exit, and set_exception_at_thread_exit acquire a single mutex associated with the promise object while updating the promise object.
An exception is thrown if there is no shared state or the shared state already stores a value or exception.
Calls to this function do not introduce data races with calls to get_future (but they need not synchronize with each other).

Parameters

p - exception pointer to store. The behavior is undefined if p is null.

Return value

(none)

Exceptions

std::future_error on the following conditions:

* *this has no shared state. The error category is set to no_state.

* The shared state already stores a value or exception. The error category is set to promise_already_satisfied.

Example

// Run this code

  #include <thread>
  #include <iostream>
  #include <future>

  int main()
  {
      std::promise<int> p;
      std::future<int> f = p.get_future();

      std::thread t([&p]{
          try {
              // code that may throw
              throw std::runtime_error("Example");
          } catch(...) {
              try {
                  // store anything thrown in the promise
                  p.set_exception(std::current_exception());
              } catch(...) {} // set_exception() may throw too
          }
      });

      try {
          std::cout << f.get();
      } catch(const std::exception& e) {
          std::cout << "Exception from the thread: " << e.what() << '\n';
      }
      t.join();
  }

Output:

  Exception from the thread: Example