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std::jthread::jthread(3)       C++ Standard Libary	std::jthread::jthread(3)

NAME
     std::jthread::jthread - std::jthread::jthread

Synopsis
	jthread() noexcept;			   (1) (since C++20)
	jthread( jthread&& other ) noexcept;	   (2) (since C++20)
	template< class F, class... Args >	   (3) (since C++20)
	explicit jthread( F&& f, Args&&... args );
	jthread( const jthread& ) = delete;	   (4) (since C++20)

	Constructs new std::jthread object.

	1) Creates new std::jthread object which does not represent a thread.
	2) Move constructor. Constructs the std::jthread object to represent the
     thread of
	execution that was represented by other. After this call other no longer
     represents
	a thread of execution.
	3)  Creates  new  std::jthread object and associates it with a thread of
     execution.

	The new thread of execution starts executing:

	std::invoke(decay-copy(std::forward<F>(f)),   get_stop_token(),   (until
     C++23)
		    decay-copy(std::forward<Args>(args))...)
	std::invoke(auto(std::forward<F>(f)),	get_stop_token(),	  (since
     C++23)
		    auto(std::forward<Args>(args))...)

	if the expression above is well-formed, otherwise starts executing:

	std::invoke(decay-copy(std::forward<F>(f)),	      (until C++23)
		    decay-copy(std::forward<Args>(args))...).
	std::invoke(auto(std::forward<F>(f)),		      (since C++23)
		    auto(std::forward<Args>(args))...).

	The calls of decay-copy are evaluated
	(until C++23)
	The values produced by auto are materialized
	(since C++23) in the current thread, so that any exceptions thrown  dur-
     ing evaluation
	and  copying/moving  of  the arguments are thrown in the current thread,
     without
	starting the new thread.
	These overloads participate in	overload  resolution  only  if	std::re-
     move_cvref_t<F> is
	not the same type as std::jthread.
	If any of the following is false, the program is ill-formed:
	  * std::is_constructible_v<std::decay_t<F>, F>
	  * (std::is_constructible_v<std::decay_t<Args>, Args> && ...)
	  * std::is_invocable_v<std::decay_t<F>, std::decay_t<Args>...> ||
	    std::is_invocable_v<std::decay_t<F>,    std::stop_token,	std::de-
     cay_t<Args>...>
	The completion of the invocation of the  constructor  synchronizes  with
     the beginning
	of the invocation of the copy of f on the new thread of execution.
	4)  The  copy  constructor  is deleted; threads are not copyable. No two
     std::jthread
	objects may represent the same thread of execution.

Parameters
	other - another std::jthread object to construct this  std::jthread  ob-
     ject with
	f     - Callable object to execute in the new thread
	args  - arguments to pass to the new function

Postconditions
	1)  get_id() equal to std::jthread::id() (i.e. joinable() returns false)
     and
	get_stop_source().stop_possible() is false.
	2) other.get_id() equal to std::jthread::id() and get_id()  returns  the
     value of
	other.get_id() prior to the start of construction.
	3)  get_id()  not  equal  to std::jthread::id() (i.e. joinable() returns
     true), and
	get_stop_source().stop_possible() is true.

Exceptions
	3) std::system_error if the thread could not be started.  The  exception
     may represent
	the error condition std::errc::resource_unavailable_try_again or another
	implementation-specific error condition.

Notes
	The  arguments to the thread function are moved or copied by value. If a
     reference
	argument needs to be passed to the thread function, it has to be wrapped
     (e.g. with
	std::ref or std::cref).

	Any return value from the function is ignored. If the function throws an
     exception,
	std::terminate is called. In order to pass return values  or  exceptions
     back to the
	calling thread, std::promise or std::async may be used.

Example
     // Run this code

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

      using namespace std::literals;

      void f1(int n)
      {
	  for (int i = 0; i < 5; ++i)
	  {
	      std::cout << "Thread 1 executing\n";
	      ++n;
	      std::this_thread::sleep_for(10ms);
	  }
      }

      void f2(int& n)
      {
	  for (int i = 0; i < 5; ++i)
	  {
	      std::cout << "Thread 2 executing\n";
	      ++n;
	      std::this_thread::sleep_for(10ms);
	  }
      }

      class foo
      {
      public:
	  void bar()
	  {
	      for (int i = 0; i < 5; ++i)
	      {
		  std::cout << "Thread 3 executing\n";
		  ++n;
		  std::this_thread::sleep_for(10ms);
	      }
	  }
	  int n = 0;
      };

      class baz
      {
      public:
	  void operator()()
	  {
	      for (int i = 0; i < 5; ++i)
	      {
		  std::cout << "Thread 4 executing\n";
		  ++n;
		  std::this_thread::sleep_for(10ms);
	      }
	  }
	  int n = 0;
      };

      int main()
      {
	  int n = 0;
	  foo f;
	  baz b;
	  std::jthread t0; // t0 is not a thread
	  std::jthread t1(f1, n + 1); // pass by value
	  std::jthread t2a(f2, std::ref(n)); // pass by reference
	  std::jthread	t2b(std::move(t2a));  // t2b is now running f2(). t2a is
     no longer a thread
	  std::jthread t3(&foo::bar, &f); // t3 runs foo::bar() on object f
	  std::jthread t4(b); // t4 runs baz::operator() on a copy of object b
	  t1.join();
	  t2b.join();
	  t3.join();
	  std::cout << "Final value of n is " << n << '\n';
	  std::cout << "Final value of f.n (foo::n) is " << f.n << '\n';
	  std::cout << "Final value of b.n (baz::n) is " << b.n << '\n';
	  // t4 joins on destruction
      }

Possible output:
      Thread 2 executing
      Thread 1 executing
      Thread 4 executing
      Thread 3 executing
      Thread 3 executing
      Thread 4 executing
      Thread 2 executing
      Thread 1 executing
      Thread 3 executing
      Thread 1 executing
      Thread 4 executing
      Thread 2 executing
      Thread 3 executing
      Thread 1 executing
      Thread 4 executing
      Thread 2 executing
      Thread 3 executing
      Thread 1 executing
      Thread 4 executing
      Thread 2 executing
      Final value of n is 5
      Final value of f.n (foo::n) is 5
      Final value of b.n (baz::n) is 0

	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
			    overload (3) directly required (the decayed
	LWG  3476 C++20      types of)					     re-
     moved these
			    F and the argument types to be move 	     re-
     quirements^[1]
			    constructible

	 1. a The move-constructibility is already indirectly required by
	    std::is_constructible_v.

See also
	constructor   constructs new thread object
		      (public member function of std::thread)
	C documentation for
	thrd_create

http://cppreference.com 	   2024.06.10		std::jthread::jthread(3)
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