std::packaged_task<R(Args...)>::make_ready_at_thread_exit

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

Calls the stored task as if by INVOKE<R>(f, args...), where f is the stored task. 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 <chrono>
#include <functional>
#include <future>
#include <iostream>
#include <thread>
#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

See also

 executes the function
(public member function)
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