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std::promis...thread_exit(3)   C++ Standard Libary  std::promis...thread_exit(3)

NAME
     std::promise::set_value_at_thread_exit				       -
     std::promise::set_value_at_thread_exit

Synopsis
	Main template
	void set_value_at_thread_exit( const R& value ); (1) (since C++11)
	void set_value_at_thread_exit( R&& value );	 (2) (since C++11)
	std::promise<R&> specializations
	void set_value_at_thread_exit( R& value );	 (3) (since C++11)
	std::promise<void> specialization
	void set_value_at_thread_exit();		 (4) (since C++11)

	Stores the value into the shared state without making  the  state  ready
     immediately.
	The  state  is made ready when the current thread exits, after all vari-
     ables with
	thread-local storage duration have been destroyed.

	The   operation   behaves   as	  though    set_value,	  set_exception,
     set_value_at_thread_exit,
	and  set_exception_at_thread_exit acquire a single mutex associated with
     the promise
	object while updating the promise object.

	Calls to this function do not introduce data races with calls to get_fu-
     ture
	(therefore they need not synchronize with each other).

Parameters
	value - value to store in the shared state

Return value
	(none)

Exceptions
	std::future_error on the following conditions:

	  * *this has no shared state. The error code is set to no_state.
	  * The shared state already stores a value or exception. The error code
     is set to
	    promise_already_satisfied.

	Additionally:

	1) Any exception thrown by the constructor selected to copy an object of
     type R.
	2) Any exception thrown by the constructor selected to move an object of
     type R.

Example
     // Run this code

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

      int main()
      {
	  using namespace std::chrono_literals;
	  std::promise<int> p;
	  std::future<int> f = p.get_future();
	  std::thread([&p]
	  {
	      std::this_thread::sleep_for(1s);
	      p.set_value_at_thread_exit(9);
	  }).detach();

	  std::cout << "Waiting... " << std::flush;
	  f.wait();
	  std::cout << "Done!\nResult is: " << f.get() << '\n';
      }

Output:
      Waiting... Done!
      Result is: 9

	Defect reports

	The following behavior-changing defect	reports  were  applied	retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to		 Behavior as published		    Cor-
     rect behavior
	LWG 2098 C++11	    it was unclear which exceptions are required to made
     clear
			    be thrown

See also
	set_value		     sets the result to specific value
				     (public member function)
				     sets  the	result	to indicate an exception
     while
	set_exception_at_thread_exit delivering the notification only at  thread
     exit
				     (public member function)

http://cppreference.com 	   2024.06.10	    std::promis...thread_exit(3)
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