NAME

std::promise::set_exception - std::promise::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
(therefore 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 code is set to no_state.

* The shared state already stores a value or exception. The error code 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());
// or throw a custom exception instead
// p.set_exception(std::make_exception_ptr(MyException("mine")));
} 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