std::promise::set_exception

C++

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Language support library

Concepts library (C++20)

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Regular expressions library (C++11)

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Technical Specifications

Thread support library

Threads
thread (C++11)
hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)
this_thread namespace
get_id (C++11) yield (C++11)	sleep_for (C++11) sleep_until (C++11)
Mutual exclusion
mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17)	timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14)
Generic lock management
lock_guard (C++11) scoped_lock (C++17) unique_lock (C++11) shared_lock (C++14) defer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11)	lock (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lock (C++11)(C++11)(C++11) once_flag (C++11) call_once (C++11)
Condition variables
condition_variable (C++11)
condition_variable_any (C++11)
notify_all_at_thread_exit (C++11)
cv_status (C++11)
Futures
promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11)	launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11)

std::promise

Member functions

promise::promise

promise::~promise

promise::operator=

promise::swap

Getting the result

promise::get_future

Setting the result

promise::set_value

promise::set_value_at_thread_exit

promise::set_exception

promise::set_exception_at_thread_exit

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.

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

See also

set_exception_at_thread_exit

sets the result to indicate an exception while delivering the notification only at thread exit (public member function)