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Introduction to std::packaged_task

Explore how to use std::packaged_task to wrap callables and execute them asynchronously in C++. Understand creating futures, running tasks in threads, and collecting results through a practical example that sums numbers across multiple threads.

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std::packaged_task pack is a wrapper for a callable, which allows it to be invoked asynchronously. By calling pack.get_future(), we get the associated future. Invoking the call operator on pack (pack()) executes the std::packaged_task and, therefore, executes the callable.

Dealing with std::packaged_task usually consists of four steps:

I. Wrap our work:

C++
std::packaged_task<int(int, int)> sumTask([](int a, int b){ return a + b; });

II. Create a future:

C++
std::future<int> sumResult= sumTask.get_future();

III. Perform the calculation:

C++
sumTask(2000, 11);

IV. Query the result:

C++
sumResult.get();

Here is an example ...