Std::promise::set_exception (3) Linux Manual Page

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

std::promise::set_exception (3) Linux Manual Page