c++ std::packaged_task

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c++ std::future

std::packaged_task

c++ std::packaged_task wraps a callable object, which can be invoked asynchronously.

It stores a value in a share state, which can be accessed by std::future.

class :

std::packaged_task<R>;

Methods :

.valid	- Check if the object has a valid function

.swap

.get_future

.operator()	- Invoke the function

.make_ready_at_thread_exit

.reset	- Reset: abandon any stored results.

c++ Example

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

int main()
{
	static std::mt19937 rnd{std::mt19937_64{std::mt19937{std::mt19937_64{std::random_device{}()}()}()}()};

	std::packaged_task<void(void)> task{
		[]
		{
			if (rnd() %2 == 0)
				throw std::runtime_error{
					"test exception on"
				};
			std::cout << "Hello, c++!" << std::endl;
		}
	};
	std::future<void> future = task.get_future();

	std::thread thread{
		[task = std::move(task)]
			mutable
		{
			task();
		}
	};
	try
	{
		future.get();
	}
	catch (const std::exception & e)
	{
		std::cerr << "ERROR: " << e.what() << std::endl;
	}
	thread.join();
}

///////////////////////////////////////////////////////////////////////////////

Mon Oct 12 10:37:07 PM UTC 2026

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