std::jthread::jthread
jthread() noexcept; |
(1) | (since C++20) |
jthread( jthread&& other ) noexcept; |
(2) | (since C++20) |
template< class F, class... Args > explicit jthread( F&& f, Args&&... args ); |
(3) | (since C++20) |
jthread( const jthread& ) = delete; |
(4) | (since C++20) |
Constructs new std::jthread
object.
std::jthread
object which does not represent a thread.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 After this call other no longer represents a thread of execution.std::jthread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(), decay-copy(std::forward<Args>(args))...)
|
(until C++23) |
std::invoke(auto(std::forward<F>(f)), get_stop_token(), |
(since C++23) |
if the expression above is well-formed, otherwise starts executing:
std::invoke(decay-copy(std::forward<F>(f)), decay-copy(std::forward<Args>(args))...).
|
(until C++23) |
std::invoke(auto(std::forward<F>(f)), |
(since C++23) |
std::jthread
.- 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::decay_t<Args>...>
std::jthread
objects may represent the same thread of execution.Contents |
[edit] 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 |
[edit] Postconditions
get_id()
equal to std::jthread::id() (i.e. joinable()
returns false) and get_stop_source().stop_possible() is false.get_id()
returns the value of other.get_id() prior to the start of construction.get_id()
not equal to std::jthread::id() (i.e. joinable()
returns true), and get_stop_source().stop_possible() is true.[edit] Exceptions
std::errc::resource_unavailable_try_again
or another implementation-specific error condition.[edit] 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.
[edit] 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 }
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
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
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 these requirements[1] |
- ↑ The move-constructibility is already indirectly required by std::is_constructible_v.
[edit] See also
constructs new thread object (public member function of std::thread )
| |
C documentation for thrd_create
|