NAME

std::packaged_task::make_ready_at_thread_exit - std::packaged_task::make_ready_at_thread_exit

Synopsis

void make_ready_at_thread_exit( ArgTypes... args ); (since C++11)

Calls the stored task with forwarded args as the arguments. The return value of the
task or any exception thrown by it is stored in the shared state of *this.

The shared state is only made ready after the current thread exits and all objects
of thread local storage duration are destroyed.

Parameters

args - the parameters to pass on invocation of the stored task

Return value

(none)

Exceptions

std::future_error on the following error conditions:

* The stored task has already been invoked. The error category is set to
promise_already_satisfied.
* *this has no shared state. The error category is set to no_state.

Example

// Run this code

#include <future>
#include <iostream>
#include <chrono>
#include <thread>
#include <functional>
#include <utility>

void worker(std::future<void>& output)
{
std::packaged_task<void(bool&)> my_task{ [](bool& done) { done=true; } };

auto result = my_task.get_future();

bool done = false;

my_task.make_ready_at_thread_exit(done); // execute task right away

std::cout << "worker: done = " << std::boolalpha << done << std::endl;

auto status = result.wait_for(std::chrono::seconds(0));
if (status == std::future_status::timeout)
std::cout << "worker: result is not ready yet" << std::endl;

output = std::move(result);
}

int main()
{
std::future<void> result;

std::thread{worker, std::ref(result)}.join();

auto status = result.wait_for(std::chrono::seconds(0));
if (status == std::future_status::ready)
std::cout << "main: result is ready" << std::endl;
}

Output:

worker: done = true
worker: result is not ready yet
main: result is ready