std::promise<R>::set_exception

 

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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

Non-member Functions

swap(std::promise)

Helper Classes

uses_allocator<std::promise>

 

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

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)