Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::atomic...::atomic_ref(3) C++ Standard Libarystd::atomic...::atomic_ref(3)

NAME
       std::atomic_ref::atomic_ref - std::atomic_ref::atomic_ref

Synopsis
	  explicit atomic_ref( T& obj );		(1) (since C++20)
	  atomic_ref( const atomic_ref&	ref ) noexcept;	(2) (since C++20)

	  Constructs a new atomic_ref object.

	  1)  Constructs  an atomic_ref	object referencing the object obj. The
       behavior	is
	  undefined if obj is not aligned to required_alignment.
	  2) Constructs	an atomic_ref object referencing the object referenced
       by ref.

Parameters
	  obj -	object to reference
	  ref -	another	atomic_ref object to copy from

Example
	  The program increments the  values  in  a  container	using  several
       threads.	Then the
	  final	 sum  is  printed. Non-atomic access may "loss"	the results of
       some operations
	  due to data-races.

       // Run this code

	#include <atomic>
	#include <thread>
	#include <vector>
	#include <numeric>
	#include <iostream>

	int main()
	{
	    using Data = std::vector<char>;

	    auto inc_atomically	= [](Data& data) {
		for (Data::value_type& x : data) {
		    auto xx = std::atomic_ref<Data::value_type>(x);
		    ++xx;  // atomic read-modify-write
		}
	    };

	    auto inc_directly =	[](Data& data) {
		for (Data::value_type& x : data)
		    ++x;
	    };

	    auto test_run = [](const auto Fun) {
		Data data(10'000'000);
		{
		    std::jthread j1 {Fun, std::ref(data)};
		    std::jthread j2 {Fun, std::ref(data)};
		    std::jthread j3 {Fun, std::ref(data)};
		    std::jthread j4 {Fun, std::ref(data)};
		}
		std::cout  <<  "sum  =	"   <<	 std::accumulate(cbegin(data),
       cend(data), 0) << '\n';
	    };

	    test_run(inc_atomically);
	    test_run(inc_directly);
	}

Possible output:
	sum = 40000000
	sum = 39994973

http://cppreference.com		  2022.07.31	 std::atomic...::atomic_ref(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::atomic_ref::atomic_ref&sektion=3&manpath=FreeBSD+Ports+15.0>

home | help