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Defined in header <future>
template< class > class packaged_task; //not defined
(1) (since C++11)
template< class R, class ...Args >
class packaged_task<R(Args...)>;
(2) (since C++11)

The class template std::packaged_task wraps any Callable target (function, lambda expression, bind expression, or another function object) so that it can be invoked asynchronously. Its return value or exception thrown is stored in a shared state which can be accessed through std::future objects.

Just like std::function, std::packaged_task is a polymorphic, allocator-aware container: the stored callable target may be allocated on heap or with a provided allocator.


[edit] Member functions

constructs the task object
(public member function) [edit]
destructs the task object
(public member function) [edit]
moves the task object
(public member function) [edit]
checks if the task object has a valid function
(public member function) [edit]
swaps two task objects
(public member function) [edit]
Getting the result
returns a std::future associated with the promised result
(public member function) [edit]
executes the function
(public member function) [edit]
executes the function ensuring that the result is ready only once the current thread exits
(public member function) [edit]
resets the state abandoning any stored results of previous executions
(public member function) [edit]

[edit] Non-member functions

specializes the std::swap algorithm
(function template) [edit]

[edit] Helper classes

specializes the std::uses_allocator type trait
(class template specialization) [edit]

[edit] Example

#include <iostream>
#include <cmath>
#include <thread>
#include <future>
#include <functional>
// unique function to avoid disambiguating the std::pow overload set
int f(int x, int y) { return std::pow(x,y); }
void task_lambda()
    std::packaged_task<int(int,int)> task([](int a, int b) {
        return std::pow(a, b); 
    std::future<int> result = task.get_future();
    task(2, 9);
    std::cout << "task_lambda:\t" << result.get() << '\n';
void task_bind()
    std::packaged_task<int()> task(std::bind(f, 2, 11));
    std::future<int> result = task.get_future();
    std::cout << "task_bind:\t" << result.get() << '\n';
void task_thread()
    std::packaged_task<int(int,int)> task(f);
    std::future<int> result = task.get_future();
    std::thread task_td(std::move(task), 2, 10);
    std::cout << "task_thread:\t" << result.get() << '\n';
int main()


task_lambda: 512
task_bind:   2048
task_thread: 1024

[edit] See also

waits for a value that is set asynchronously
(class template) [edit]