std::promise<R>::set_exception

 

C++

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Technical Specifications

 

Thread support library

Threads
thread (C++11)
hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)
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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

 

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

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)