std::jthread::jthread

Since C++20

Constructs new std::jthread object.

# Declarations

jthread() noexcept;

(since C++20)

jthread( jthread&& other ) noexcept;

(since C++20)

template< class F, class... Args >
explicit jthread( F&& f, Args&&... args );

(since C++20)

jthread( const jthread& ) = delete;

(since C++20)

# Parameters

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

# 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

#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
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 3476	C++20	overload (3) directly required (the decayed types of)F and the argument types to be move constructible	removed theserequirements[1]

std::jthread::jthread

# Declarations

# Parameters

# Notes

# Example

# Defect reports

# See also