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Difference between revisions of "cpp/thread/packaged task"

From cppreference.com
< cpp‎ | thread
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===Member functions===
 
===Member functions===
 
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===Non-member functions===
 
===Non-member functions===
 
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===Helper classes===
 
===Helper classes===
 
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===See also===
 
===See also===
 
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Revision as of 22:28, 31 May 2013

 
C++
 
Concurrency support library
Threads
(C++11)
(C++20)
(C++17)(C++17)
this_thread namespace
(C++11)
(C++11)
(C++11)
(C++11)
Cooperative cancellation
Mutual exclusion
(C++11)
(C++11)
(C++17)
Generic lock management
(C++11)
(C++11)
(C++17)
(C++11)
(C++14)
(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)
Condition variables
(C++11)
(C++11)
(C++11)
(C++11)
Semaphores
(C++20)(C++20)
Latches and Barriers
(C++20)
(C++20)
Futures
(C++11)
(C++11)
(C++11)
packaged_task
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Safe Reclamation
(C++26)
(C++26)
(C++26)
Hazard Pointers
(C++26)
(C++26)
(C++26)
Atomic types
(C++11)
(C++20)
(C++11)
Initialization of atomic types
(C++11)(deprecated in C++20)
(C++11)(deprecated in C++20)
(C++11)
Memory ordering
(C++11)
(C++11)
(C++11)
(C++11)
Free functions for atomic operations
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++26)(C++26)
(C++26)(C++26)
(C++11)
(C++20)(C++20)
(C++20)
(C++20)
Free functions for atomic flags
(C++11)(C++11)
(C++11)(C++11)
(C++20)(C++20)
(C++20)(C++20)
(C++20)
(C++20)
 
std::packaged_task
 
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.

Contents

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]
Execution
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]

Non-member functions

(C++11)
 specializes the std::swap algorithm
(function template) [edit]

Helper classes

(C++11) (until C++17)
 specializes the std::uses_allocator type trait
(class template specialization) [edit]

Example

Run this code
#include <iostream>
#include <cmath>
#include <thread>
#include <future>
#include <functional>
 
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(std::pow, 2, 11));
    std::future<int> result = task.get_future();
 
    task();
 
    std::cout << "task_bind:\t" << result.get() << '\n';
}
 
void task_thread()
{
    std::packaged_task<int(int,int)> task(std::pow);
    std::future<int> result = task.get_future();
 
    std::thread task_td(std::move(task), 2, 10);
    task_td.join();
 
    std::cout << "task_thread:\t" << result.get() << '\n';
}
 
int main()
{
    task_lambda();
    task_bind();
    task_thread();
}

Output: 

task_lambda: 512
task_bind:   2048
task_thread: 1024

See also

(C++11)
 waits for a value that is set asynchronously
(class template) [edit]
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