std::jthread::jthread - cppreference.com (original) (raw)

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 After this call other no longer represents a thread of execution.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:

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

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 during 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::remove_cvref_t<F> is not the same type as std::jthread.

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.

1. The copy constructor is deleted; threads are not copyable. No two std::jthread objects may represent the same thread of execution.

Contents

• 1 Parameters
• 2 Postconditions
• 3 Exceptions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[edit] Postconditions

1. other.get_id() equal to

std::jthread::id()

and get_id() returns the value of other.get_id() prior to the start of construction.

[edit] Exceptions

1. 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.

[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 #include #include #include   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.

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

[edit] See also